JP2008288087A - Beam measuring device, beam measuring method, and pump/probe measuring method using the device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a beam measurement device, a beam measurement method, and a pump/probe measurement method that use them, wherein three-dimensional measurement of quantum beams can be carried out simply and easily. <P>SOLUTION: This beam measurement device 100 is equipped with a light source part 10 for shaping the pulse wave form of the pulse laser beam oscillated by a laser oscillator 11 so that the wavelength of the pulse laser beam is changed, according to time; an incident optical system 20 having a delay element 23 which gives time delay according to the incident position with respect to the pulse laser beam emitted from the light source part 10 and a polarized light conversion element 24, which converts a pulse laser beam into a different polarization state according to the incident position; an electro-optical element 30 having a different crystalline axis according to the incident position; a polarizer 46 to take out prescribed components from the pulse laser beam; and an optical spectrometer 50 to measure spectrum of the taken out spectrum of a pulse laser beam extracted from the polarizer 46. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a beam measuring apparatus, a beam measuring method, and a pump / probe measuring method using the same, and more particularly, a beam measuring apparatus, a beam measuring method, and a pump / probe measurement using the same. Regarding the method.

  In recent years, accelerators that accelerate charged particles such as electron beams have been widely used. For example, in X-FEL (X-ray Free Electron Laser) and ERL (Energy-Recovery Linac), a short bunch electron beam is accelerated to near the speed of light. Then, coherent synchrotron radiation emitted from an insertion light source such as an undulator is used. In such an accelerator, it is necessary to install a short bunch beam monitor in order to obtain a high-quality electron beam. The characteristics of the beam measured by such a beam monitor include the lateral profile of the charged particle beam, the beam position, energy, and bunch length. It is also desirable to measure a charged particle beam nondestructively. Further, in order to obtain a femtosecond bunch, it is desired to measure these bunch information in one shot without jitter.

  For example, a method for measuring the bunch length of an electron beam using an electro-optic crystal is disclosed (Non-Patent Document 1). In this measurement method, pulsed laser light is incident on the electro-optic crystal. Further, when the electron beam passes through the electro-optic crystal, an electric field is generated by the electron beam. This electric field changes the polarization state of the pulsed laser light passing through the electro-optic crystal. For example, when passing through an electro-optic crystal, linearly polarized light changes to elliptically polarized light. Information on the bunch length can be acquired by measuring the pulse laser beam that has passed through the electro-optic crystal.

  Further, a method has been proposed in which electrodes are arranged in a vacuum chamber and the beam position in the lateral direction is monitored (Patent Document 2). In this method, four electrodes are arranged in the beam path. These four electrodes are arranged point-symmetrically in a plane perpendicular to the beam direction. Thereby, the spatial distribution of the bunches in the plane perpendicular to the beam direction can be measured.

I. Wilke et. al. "Single-Shot Electron-Beam Bunch Length Measurements" Physical Review Letters Volume 88 124801 Number 12 T.A. Suwada "Multipole Analysis of Electromagnetic Field Generated by Single-Bunch Electron Beams" Jpn. J. et al. Appl. Phys. Vol. 40 (2001) pp 890-897

  However, the conventional measurement method has a problem that it is difficult to measure the quantum beam three-dimensionally.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a beam measuring apparatus, a beam measuring method, and a beam measuring apparatus capable of easily performing three-dimensional measurement of a quantum beam. It is to provide a method for measuring the pump probe used.

  A beam measuring apparatus according to a first aspect of the present invention is a beam measuring apparatus that three-dimensionally measures a quantum beam using a pulsed laser beam, and the wavelength of the pulsed laser beam oscillated by a laser oscillator depends on time. A light source unit that shapes and emits a pulse waveform of the pulsed laser light, and a first delay element that gives a time delay corresponding to an incident position with respect to the pulsed laser light emitted from the light source unit, An incident optical system having a first polarization conversion element that converts the pulsed laser light into a different polarization state according to an incident position; and a crystal axis that is different depending on the incident position. An electro-optic element, a polarizer that extracts a predetermined polarization component from pulsed laser light incident from the incident optical system via the electro-optic element, and a polarizer that is extracted by the polarizer. A measuring device for measuring the spectrum of the pulsed laser light, but with a. Thereby, since the three-dimensional information of the quantum beam is developed in the spectrum, the three-dimensional measurement of the quantum beam can be easily performed.

  A beam measuring apparatus according to a second aspect of the present invention is the above-described beam measuring apparatus, wherein the electro-optic element has a plurality of electric elements arranged radially so that the crystal axes of the electro-optic element are radial. An optical crystal is provided. Thereby, since the change of the refractive index in an electro-optic element can be enlarged, it can measure correctly.

  The beam measurement apparatus according to a third aspect of the present invention is the beam measurement apparatus described above, wherein the first polarization conversion element has a plurality of radially divided areas, and the light of the pulse laser beam. In a plane perpendicular to the axis, a plurality of electro-optic crystals provided in the electro-optic element are arranged at positions corresponding to the divided regions provided in the first polarization conversion element, and enter the electro-optic element. The first polarization conversion element converts the polarization state so that the vibration plane of the electric vector of the pulse laser beam is in the same direction as the radial crystal axis. Thereby, since the change of the polarization state by the electro-optic element can be increased, the measurement can be performed accurately.

  A beam measuring apparatus according to a fourth aspect of the present invention is the above-described beam measuring apparatus, wherein the first delay element corresponds to a plurality of divided regions provided in the first polarization conversion element. The pulsed laser light is delayed stepwise according to the incident position. Thereby, the spatial distribution in the horizontal direction can be easily measured.

  A beam measuring apparatus according to a fifth aspect of the present invention is the above-described beam measuring apparatus, wherein the stepwise delay time provided by the first delay element is longer than the pulse of the quantum beam. Is. Thereby, the spatial distribution in the horizontal direction can be measured more easily.

  A beam measuring apparatus according to a sixth aspect of the present invention is the above-described beam measuring apparatus, wherein the plurality of divided regions provided in the first polarization conversion element are emitted while shifting the phase of incident light. Each of the wave plates is provided, and the optical axes of the wave plates are substantially orthogonal in the opposed divided regions. Thereby, since it can convert into a desired polarization state, it can measure simply.

  A beam measuring apparatus according to a seventh aspect of the present invention is the above-described beam measuring apparatus, wherein the maximum delay time given by the first delay element is a pulse width of the pulse laser beam emitted from the light source unit. The pulse laser beam that has been given a time delay by the first delay element has an overlap period in which the pulse laser beam overlaps the entire outer circumference of the optical axis of the pulse laser beam. It is what. Thereby, since the polarization state changes in all directions of the electro-optic element, the spatial distribution in the lateral direction can be measured more easily.

  A beam measuring apparatus according to an eighth aspect of the present invention is the above-described beam measuring apparatus, wherein the pulse of the quantum beam is synchronized with a timing at which the pulse laser beam in the overlapping period passes through the electro-optic element. , Passing through the electro-optic element. Accordingly, since the polarization state changes in all directions of the electro-optic element, the spatial distribution in the lateral direction of the bunch can be measured more easily.

  A beam measuring apparatus according to a ninth aspect of the present invention is the beam measuring apparatus described above, wherein a time delay corresponding to an incident position is given to the pulse laser beam emitted from the electro-optic element, and the polarizer A second delay element that shortens a pulse width of the light incident on the laser beam, and a nonlinear optical element in which a part of the pulsed laser light oscillated by the laser oscillator is incident as reference light, and the polarizer is in the polarization direction. In response, the pulsed laser beam is branched, one branched light branched by the polarizer is measured by the measuring device, the other branched light branched by the polarizer is incident on the nonlinear optical element, and the nonlinear The light generated by the non-linear optical effect in the non-linear optical element is measured by an array photodetector by intersecting with the reference light in the optical element. Thereby, a time distribution can be measured simply and accurately.

  A beam measuring apparatus according to a tenth aspect of the present invention is the beam measuring apparatus described above, wherein the pulse is emitted before entering the first delay element and after exiting the second delay element. The pulse widths of the laser beams are substantially equal. The time distribution of the beam can be measured more easily and accurately.

  A beam measuring apparatus according to an eleventh aspect of the present invention is the beam measuring apparatus described above, wherein the electro-optic element is provided with a hollow portion through which the quantum beam passes. This allows non-destructive measurement.

  A beam measuring apparatus according to a twelfth aspect of the present invention is the above-described beam measuring apparatus, further comprising a pair of axicon lenses that make the pulsed laser light incident on the electro-optic element into an annular shape, An annular pulse laser beam passes outside the hollow portion. Thereby, the utilization efficiency of light can be improved and it can measure more correctly.

  A beam measuring apparatus according to a thirteenth aspect of the present invention is the beam measuring apparatus described above, comprising a second polarization conversion element on which the pulse laser beam emitted from the electro-optic element is incident, and the second polarized light The conversion element converts to a different polarization state depending on the incident position. Thereby, the apparatus configuration can be simplified.

  A beam measuring apparatus according to a fourteenth aspect of the present invention is the beam measuring apparatus described above, wherein the first polarization conversion element and the second polarization conversion element have optical axes in the same direction. It is what. Thereby, the apparatus configuration can be simplified.

  A beam measuring apparatus according to a fifteenth aspect of the present invention is the beam measuring apparatus described above, wherein the measuring instrument is a spectroscopic measuring instrument that performs spectrum measurement by splitting the pulse laser beam. Thereby, the apparatus configuration can be simplified.

  A beam measuring apparatus according to a sixteenth aspect of the present invention is the above-described beam measuring apparatus, wherein the spectrum of one pulse of the pulsed laser beam is obtained in one frame of the array detector provided in the spectrometer. It is what is done. Thereby, it can measure simply.

  A beam measuring method according to a seventeenth aspect of the present invention is a beam measuring method for three-dimensionally measuring a quantum beam using a pulsed laser beam, wherein the wavelength of the pulsed laser beam oscillated by a laser oscillator depends on time. Step of shaping and emitting the pulse waveform of the pulsed laser beam so as to change, and providing a time delay corresponding to the incident position with respect to the shaped pulsed laser beam, and bringing the pulsed laser beam to the incident position A step of converting to a different polarization state according to the step, and a step of causing the pulsed laser light provided with the time delay to be incident on an electro-optical element that is disposed in a beam path of the quantum beam and has a different crystal axis depending on an incident position. Extracting a predetermined polarization component from the pulsed laser light emitted from the electro-optic element; and from the pulsed laser light. Measuring the spectrum of the predetermined polarization component issued Ri are those comprising a. Thereby, since the three-dimensional information of the quantum beam is developed in the spectrum, the three-dimensional measurement of the quantum beam can be easily performed.

  A beam measuring method according to an eighteenth aspect of the present invention is the beam measuring method described above, wherein a plurality of electric electrodes arranged radially on the electro-optic element are arranged so that the crystal axes of the electro-optic element are radial. An optical crystal is provided.

  A beam measurement method according to a nineteenth aspect of the present invention is the beam measurement method described above, wherein in the step of converting the pulse laser beam to a different polarization state according to the incident position, the pulse laser beam is radially divided. A plurality of electro-optic crystals provided on the electro-optic element in a plane perpendicular to the optical axis of the pulsed laser light are incident on a first polarization conversion element having a plurality of divided regions. It is arranged at a position corresponding to the divided region provided in the conversion element, and the vibration plane of the electric vector of the pulsed laser light incident on the electro-optic element is in the same direction as the radial crystal axis. The polarization conversion element converts the polarization state. Thereby, since the change of the polarization state by the electro-optic element can be increased, the measurement can be performed accurately.

  A beam measurement method according to a twentieth aspect of the present invention is the beam measurement method described above, wherein a time delay corresponding to the incident position is caused by the first delay element provided in the optical path of the pulse laser beam. The first delay element delays the pulsed laser beam stepwise according to the incident position so as to correspond to a plurality of divided regions provided in the first polarization conversion element. Thereby, the spatial distribution in the horizontal direction can be easily measured.

  The beam measurement method according to a twenty-first aspect of the present invention is the beam measurement method described above, wherein the stepwise delay time provided by the first delay element is longer than the pulse of the quantum beam. Is. Thereby, the spatial distribution in the horizontal direction can be measured more easily.

  A beam measurement method according to a twenty-second aspect of the present invention is the beam measurement method described above, wherein the incident light is emitted with a phase shifted to a plurality of divided regions provided in the first polarization conversion element. Each of the wave plates is provided, and the optical axes of the wave plates are substantially orthogonal in the opposed divided regions. Thereby, since it can convert into a desired polarization state, it can measure simply.

  A beam measurement method according to a twenty-third aspect of the present invention is the beam measurement method described above, wherein a maximum delay time given to the pulse laser beam is greater than a pulse width of the pulse laser beam emitted from the light source unit. The pulse laser beam which is shortened and given the time delay has an overlapping period in which the pulse laser beam overlaps in time over the entire optical axis of the pulse laser beam. Thereby, since the polarization state changes in all directions of the electro-optic element, the spatial distribution in the lateral direction can be measured more easily.

  A beam measurement method according to a twenty-fourth aspect of the present invention is the beam measurement method described above, wherein the pulse of the quantum beam is synchronized with a timing at which the pulse laser beam of the overlapping time passes through the electro-optic element. , Passing through the electro-optic element. Thereby, since the polarization state changes in all directions of the electro-optic element, the spatial distribution in the lateral direction can be measured more easily.

  A beam measurement method according to a twenty-fifth aspect of the present invention is the beam measurement method described above, wherein the pulse laser beam emitted from the electro-optic element is given a time delay according to the incident position, and the pulse width is increased. A step of shortening, and a step of causing a part of the pulsed laser light oscillated by the laser oscillator to enter the nonlinear optical element as a reference light, and the step of extracting a predetermined polarization component from the pulsed laser light, In the step of branching pulsed laser light according to the polarization direction using a polarizer and measuring the spectrum, the spectrum of one branched light branched by the polarizer is measured, and the other branched by the polarizer The branched light is incident on the nonlinear optical element, crossed with the reference light in the nonlinear optical element, and nonlinear optical effect in the nonlinear optical element Thus the generated light is to measure the array detector. Thereby, the vertical direction distribution (time distribution) can be measured easily and accurately.

  A beam measurement method according to a twenty-sixth aspect of the present invention is the beam measurement method described above, wherein the pulse of the pulse laser beam is emitted before entering the electro-optic element and after the pulse width is shortened. The widths are substantially equal. Thereby, the vertical direction distribution (time distribution) can be measured more easily and accurately.

  A beam measurement method according to a twenty-seventh aspect of the present invention is the beam measurement method described above, wherein the electro-optical element is provided with a hollow portion through which the quantum beam passes, and the quantum beam is provided in the electro-optical element. It passes through the hollow part. This allows non-destructive measurement.

  A beam measurement method according to a twenty-eighth aspect of the present invention is the beam measurement method described above, further comprising a pair of axicon lenses that make the pulsed laser light incident on the electro-optic element into an annular shape, An annular pulse laser beam passes outside the hollow portion. Thereby, the utilization efficiency of light can be improved and it can measure more correctly.

  A beam measurement method according to a twenty-ninth aspect of the present invention is the beam measurement method described above, further comprising a step of converting the pulse laser beam emitted from the electro-optic element into a different polarization state depending on an incident position. It is. Thereby, it can measure simply.

  A beam measurement method according to a thirtieth aspect of the present invention is the beam measurement method described above, wherein the first polarization conversion element that converts the shaped pulsed laser light into a different polarization state according to an incident position; The second electro-optical element that converts the pulsed laser light emitted from the electro-optical element into a different polarization state according to the incident position has a wave plate having optical axes in the same direction. Thereby, it can measure with a simple structure.

  A beam measurement method according to a thirty-first aspect of the present invention is the beam measurement method described above, wherein, in the step of measuring the spectrum, a spectrophotometer that performs spectrum measurement is performed using the pulsed laser beam. Measure. Thereby, it can measure simply.

  A beam measurement method according to a thirty-second aspect of the present invention is the beam measurement method described above, wherein a spectrum of one pulse of the pulsed laser beam is obtained in one frame of an array detector provided in the spectrometer. It is what is done. Thereby, it can measure simply.

  A pump / probe measurement method according to a thirty-third aspect of the present invention is a pump / probe measurement method using the beam measured by the beam measurement method, wherein a predetermined polarization component is extracted from the pulse laser beam. Then, in the step of branching the pulsed laser light according to the polarization direction using a polarizer and measuring the spectrum, the spectrum of one branched light branched by the polarizer is measured and branched by the polarizer. The other branched light is amplified by NOPA, irradiated to the sample as one of pump light and probe light, and irradiated to the sample as the other of pump light and probe light with the quantum beam or the emitted light from the quantum beam. To do. Thereby, the problem of timing jitter can be improved.

  According to the present invention, it is possible to provide a beam measuring apparatus, a beam measuring method, and a pump / probe measuring method using the beam measuring apparatus, which can easily perform three-dimensional measurement of a quantum beam.

  Hereinafter, embodiments to which the present invention can be applied will be described. The following description is to describe the embodiment of the present invention, and the present invention is not limited to the following embodiment. For clarity of explanation, the following description is omitted and simplified as appropriate. Further, those skilled in the art will be able to easily change, add, and convert each element of the following embodiments within the scope of the present invention. In addition, what attached | subjected the same code | symbol in each figure has shown the same element, and abbreviate | omits description suitably.

  First, the principle of the beam measurement method according to this embodiment will be briefly described. In the present embodiment, the electro-optic element is disposed in the electron beam path. That is, the electro-optic element is disposed in a vacuum chamber that is a path of an electron beam. Further, in synchronization with the electron beam, pulsed laser light is incident on the electro-optic element. At this time, the refractive index of the electro-optic element changes due to the electric field generated by the electron beam. For this reason, the polarization state of the pulsed laser light changes according to the shape of the electron beam. Further, the electric field applied to the electro-optic element changes depending on the bunch (pulse) shape (bunch length, lateral distribution, etc.) of the electron beam. By measuring the pulse laser beam that has passed through the electro-optic element, the bunch shape of the electron beam can be measured. That is, the polarization state of the pulsed laser light changes according to the bunch shape of the electron beam. By measuring the phase change of the pulse laser beam in the electro-optic element, the electric field generated by the bunch can be known. Further, here, the pulsed laser beam that has passed through the electro-optic element is measured by spectroscopy.

  A measuring apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram schematically illustrating a configuration of a beam measuring apparatus 100 according to the first embodiment. In the middle of the description of FIG. 1, the description will be made with reference to FIGS.

  The beam measuring apparatus according to the present embodiment includes a light source unit 10, an incident optical system 20, an electro-optical element 30, an output optical system 40, a spectrometer 50, and a processing device 55. The beam measuring apparatus 100 monitors the three-dimensional bunch shape of the electron beam 31 accelerated by the accelerator. More specifically, the beam measuring apparatus 100 acquires information regarding the spatial distribution and time distribution of the electron beam 31. The electrons of the electron beam 31 are given sufficiently high energy and are accelerated to near the speed of light in vacuum. That is, the electrons are accelerated to a relativistic region. The electron beam 31 is accelerated using radio frequency (RF). For this reason, bunches having a predetermined bunch length are repeated. The beam measuring apparatus 100 measures the bunch length. Furthermore, by using the beam measuring apparatus 100, the spatial distribution when one bunch is sliced can be measured.

  First, the light source unit 10 will be described. The light source unit 10 includes a laser oscillator 11, a broadening member 12, a chirping pulse waveform shaper 13, a wave plate 14, and a Glan laser / Karlsite polarizer 15. The laser oscillator 11 oscillates pulsed laser light having a predetermined pulse width. As the laser oscillator 11, for example, a titanium sapphire laser can be used. The pulsed laser light from the laser oscillator 11 is a parallel light beam. In the following description, the optical axis direction of the laser light is defined as the Z direction, and a plane perpendicular to the Z direction is defined as the XY plane. The Z direction is a Longitudinal direction (vertical direction), and the X direction and the Y direction are Transverse directions (lateral direction). The laser light propagates along the Z axis. Therefore, the Z axis corresponds to the time axis. Further, the X direction and the Y direction in the XY plane are orthogonal to each other. As the laser oscillator 11, for example, FEMTOSOURCE SYNERGY Pro or SYNERGY 20 manufactured by Femto Lasers is used. As a result, a pulse laser beam having a pulse width of about 10 to 20 fsec oscillates.

  The broadening member 12 broadens the pulse laser beam incident from the laser oscillator 11. . For example, a photonic crystal fiber that is widely used in the field of optical communication can be used as the broadband member 12. A photonic crystal fiber is an optical fiber having a linear defect in a photonic crystal as a core and a surrounding photonic crystal as a cladding. Accordingly, the incident light propagates while being confined in the core. As the photonic crystal fiber, for example, SCG-800 manufactured by Newport can be used.

The broadband member 12 widens the wavelength width of the pulse laser beam. That is, the pulsed laser beam has a wide band due to the nonlinear optical effect in the photonic crystal fiber. The longest wavelength of the light emitted from the broadbanding member 12 is λ _L and the shortest wavelength is λ _S. As a specific example, the wavelength range of pulsed laser light is expanded to 650 nm to 1100 nm. SC (super continuum) light is emitted from the broadband member 12. The light from the broadband member 12 is white laser light. In this way, the broadband member 12 extends the spectral width. Therefore, the pulsed laser beam emitted from the broadband member 12 corresponds to a pulsed laser beam having a Fourier pulse limit of 2 to 4 fsec.

  The laser beam emitted from the broadband member 12 has a time profile as shown in FIG. FIG. 2 is a diagram showing a pulse waveform of the pulse laser beam emitted from the broadband member 12. Therefore, FIG. 2 is a graph showing the intensity distribution with respect to time of the pulse laser beam. In FIG. 2, the horizontal axis indicates time, and the vertical axis indicates the intensity of pulsed laser light. As shown in FIG. 2, the intensity of the pulse laser beam is maximized near the center of the pulse. Then, the intensity decreases toward the end of the pulse. Furthermore, the broadening member 12 widens the wavelength width of the pulse laser beam.

The pulsed laser light whose bandwidth has been widened by the broadening member 12 is incident on the chirping pulse waveform shaper 13. The chirping pulse waveform shaper 13 includes an optical modulator 13a, a pulse stretcher 13b, and an optical amplifier 13c. The chirping pulse waveform shaper 13 shapes the time waveform of the pulse laser beam. Specifically, the chirping pulse waveform shaper 13 shapes the waveform of the pulse laser beam into a rectangular shape. As the optical modulator 13a, for example, an acousto-optic (AO: Acoustic-Optics) element or a liquid crystal element can be used. More specifically, an acousto-optic spatial phase control filter (AOPDF) and a liquid crystal spatial light modulator (SLM: Spatial Light Modulator) can be used as the light modulator 13a. The optical modulator 13a modulates the spectral phase. Specifically, the phase of the pulsed laser beam is modulated so that the wavelength changes with time. Thereby, the wavelength is gradually shortened from the beginning of the pulse toward the rear side. For example, the wavelength at the front end of the pulse is the longest wavelength λ _L and the wavelength at the rear end of the pulse is the shortest wavelength λ _S. The wavelength in the laser pulse monotonously decreases from λ _L to λ _S as it goes backward. Furthermore, the relationship between wavelength and time is linear. Therefore, the wavelength decreases linearly with time.

Thus, in the laser pulse light emitted from the optical modulator 13a, the wavelength changes linearly with time. That is, the wavelength of the pulsed laser light changes linearly with time. The pulsed laser light has a spectrum between the longest wavelength λ _L and the shortest wavelength λ _S. As the optical modulator 13a of the chirping pulse waveform shaper 13, for example, DAZZLER (registered trademark) UWB-650-1100 manufactured by FASTLITE can be used. Thereby, the pulsed laser beam having a broadband spectrum of 650 to 1100 nm can be modulated. The spectrum of the pulse laser beam is modulated in accordance with a modulation signal (Acoustic Wave) input to the optical modulator 13a. Then, the chirped sound wave can freely give an optical path difference corresponding to the wavelength to the white pulse laser light passing through the crystal. The spectrum of the pulse laser beam is shaped into the same shape as the spectrum of the sound wave. Alternatively, the spectrum of the pulse laser beam may be shaped into the same shape as the pulse shape of the sound wave. The pulse stretcher 13b widens the temporal pulse width. As a result, the pulse width of the laser light becomes sufficiently longer than the bunch length of the electron beam 31 to be monitored.

  The optical amplifier 13c amplifies the incident light. For example, the optical amplifier 13c amplifies the pulse laser beam without changing the wavelength of the light. The spectrum waveform (spectrum distribution) is made rectangular. At this time, the temporal pulse waveform is also rectangular. The laser beam emitted from the chirping pulse waveform shaper 13 has a time profile as shown in FIG. FIG. 3 is a diagram showing a pulse waveform of the pulse laser beam emitted from the chirping pulse waveform shaper 13. In FIG. 3, the horizontal axis indicates time, and the vertical axis indicates the intensity of the pulsed laser beam. As shown in FIG. 3, the pulse laser beam is converted into a flat-top pulse waveform. That is, the intensity of the pulse laser beam becomes substantially constant with respect to time. For example, a waveform as shown in FIG. 3 can be obtained by adjusting the gain in accordance with the wavelength. In FIG. 3, the left side is the leading side of the pulse, and the right side is the trailing end side of the pulse. In this way, the waveform is shaped so that the time profile of the pulsed laser light is constant. The pulse waveform amplified by the optical amplifier 13c does not have to be a complete rectangle. For example, the waveform can be shaped in consideration of the pulse waveform at the stage of incidence on the electro-optic element 30 described later.

Note that. The wavelength of the pulse laser beam is changed according to time by the optical modulator 13a. Therefore, the horizontal axis in FIG. 3 can be regarded as the wavelength. In this case, FIG. 3 shows the spectrum. The optical amplifier 13c has the same intensity at each wavelength. That, is constant in intensity between the maximum wavelength lambda _L to the shortest wavelength lambda _S. Even if the wavelength changes, the intensity of the pulse laser beam does not change. Thus, the linearly chirped pulsed laser light is emitted from the chirping pulse waveform shaper 13. Regardless of the wavelength and time, the intensity of the pulsed laser light is constant. That is, the time distribution and the spectral distribution are uniform. In addition, the spectral distribution and the time distribution coincide. In the above example, the wavelength at the front end of the pulse is set to the longest wavelength λ _L and the wavelength at the rear end of the pulse is set to the shortest wavelength λ _S. That is, the wavelength at the rear end of the pulse may be the longest wavelength λ _L and the wavelength at the front end of the pulse may be the shortest wavelength λ _S. A linear chirped rectangular spectrum white laser is emitted. Note that it is also possible to perform chirping using chirped pulse amplification (CPA: Chirped Pulse Amplify). In this case, an optical path length difference is given for each wavelength by a pulse stretcher. As a result, the wavelength changes with time.

The chirped pulsed laser light is incident on the wave plate 14 and the Glan laser / Karlsite polarizer 15. Is incident on. The wave plate 14 and the Glan-laser-Karlsite polarizer 15 convert broadband white laser light having a wavelength region of 650 to 1100 nm into P-polarized light. The wave plate 14 is a half-wave plate. As the wave plate 14, for example, an achromatic 0th order crystal MgF ₂ wave plate can be used. Specifically, 10RP52-2 manufactured by Newport can be used as the wave plate 14. The wave plate 14 gives a phase difference to components that vibrate in directions orthogonal to each other. Here, a phase difference of ½ wavelength is given.

  The pulsed laser light from the light source unit 10 is incident on the Glan laser / Karlsite polarizer 15 via the wave plate 14. The Glan laser / Karlsite polarizer 15 extracts only a component in a predetermined vibration direction. Examples of the Grandlaser / Carlsite polarizer 15 include 10Gl08Ar. 16 can be used. These optical systems are described in Newport Application Note 26 “Variable Attenuator for Lasers” and Newport Application Note 28 “Supercontinuum Generation SCG-800 Photon”.

  As described above, by using the achromatic wave plate 14 and the Glan-laser-Karlsite polarizer 15, it is possible to make the white pulse laser beam in a wide band into a completely P-polarized light. The wave plate 14 is not limited to an achromatic wave plate. For example, an apochromatic wave plate that is the same transmission optical system as the achromatic wave plate can be used as the wave plate 14. Further, a periscope composed of a metal mirror or the like which is a reflection optical system may be used. Further, the amount of light can be adjusted by rotating the wave plate 14. That is, by changing the angle of the optical axis with respect to the polarization direction of the incident pulse laser beam, the ratio of the P-polarized component and the S-polarized component changes. Therefore, it is possible to adjust the light amount of the pulsed laser light that passes through the Glan-laser / carlucite polarizer 15. Of course, linearly polarized light may be extracted by using an optical element other than the wave plate 14 and the Glan-laser / Karlsite polarizer 15.

A chirped P-polarized pulse laser beam is emitted from the light source unit 10. That is, pulsed laser light whose wavelength changes with time is generated. Here, since the chirping is linear, the wavelength changes linearly with time. For example, the head of the pulsed laser beam (pulse tip) becomes the longest wavelength lambda _L, the rear side (pulse trailing edge) is the shortest wavelength lambda _S. Alternatively, the top side of the pulsed laser light is the shortest wavelength lambda _S, may become the rear side to the longest wavelength lambda _L. That is, the pulse laser beam may be chirped positively or negatively. In this manner, the light source unit 10 emits a pulse laser beam having a wide pulse width and wavelength width.

  The pulsed laser light chirped by the light source unit 10 enters the incident optical system 20. The incident optical system 20 is an optical system for causing the pulsed laser light from the light source unit 10 to enter the electro-optical element 30. The incident optical system 20 includes an axicon lens 21, an axicon lens 22, a delay element 23, a polarization conversion element 24, and a mirror 25. In FIG. 1, the polarization conversion element 24 may be disposed in front of the axicon lens 21.

A chirped P-polarized pulse laser beam is emitted from the light source unit 10. That is, pulsed laser light whose wavelength changes with time is generated. Here, since the chirping is linear, the wavelength changes linearly with time. For example, the head of the pulsed laser beam (pulse tip) becomes the longest wavelength lambda _L, the rear side (pulse trailing edge) is the shortest wavelength lambda _S. Alternatively, the top side of the pulsed laser light is the shortest wavelength lambda _S, may become the rear side to the longest wavelength lambda _L. That is, the pulse laser beam may be chirped positively or negatively. In this manner, the light source unit 10 emits a pulse laser beam having a wide pulse width and wavelength width.

  The pulsed laser light chirped by the light source unit 10 enters the incident optical system 20. The incident optical system 20 is an optical system for causing the pulsed laser light from the light source unit 10 to enter the electro-optical element 30. The incident optical system 20 includes an axicon lens 21, an axicon lens 22, a delay element 23, a polarization conversion element 24, and a mirror 25. In FIG. 1, the polarization conversion element 24 may be disposed in front of the axicon lens 21.

  The pulsed laser light from the light source unit 10 is incident on a pair of axicon lenses 21 and 22. The axicon lenses 21 and 22 have a conical shape. The axicon lenses 21 and 22 have substantially the same shape. The pulsed laser light is refracted by the pair of axicon lenses 21 and 22 and converted into a ring-shaped beam. That is, the cross section of the pulse laser beam emitted from the axicon lens 22 is a hollow ring shape. As described above, the pair of axicon lenses 21 and 22 generate an annular beam from the pulsed laser light. A parallel light beam is emitted from the axicon lens 22.

  An annular beam may be generated with a configuration other than the pair of axicon lenses 21 and 22. For example, an annular beam can be generated by one axicon lens and one spherical lens. In this way, by using one or more axicon lenses, it is possible to prevent the laser light intensity from being lowered. Alternatively, a ring-shaped slit (ring zone) may be used. By providing an annular beam converting means for converting the laser beam from the laser oscillator 11 into an annular light beam, the laser beam can be used efficiently. Further, chromatic aberration can be reduced by arranging a pair of axicon lenses symmetrically. Thereby, chromatic aberration can be reduced with respect to a broad spectrum. The axicon lens 22 emits a parallel light beam having an annular cross section. In addition, the use efficiency of light can be increased by converting the spot shape from a circular shape to an annular shape using a lens.

  The pulse laser beam emitted from the axicon lens 22 enters the delay element 23. The delay element 23 gives a time delay to the incident pulse laser beam. Specifically, a time delay corresponding to the incident position is given to the pulse laser beam. A time shift is given to light incident on different positions. As a result, the pulse width of the pulse laser beam is widened. A configuration example of the delay element 23 will be described with reference to FIG. FIG. 4A is a plan view showing the configuration of the delay element 23, and FIG. 4B is a diagram schematically showing the pulse waveform of the pulse laser beam delayed by the delay element 23.

  The delay element 23 is formed of a disk-shaped transparent plate. As shown in FIG. 4A, the delay element 23 has a divided area radially divided into eight. Here, the eight divided areas are defined as divided areas 23a to 23h. That is, in FIG. 4A, the divided regions 23a to 23h are arranged along the circumferential direction. The sizes of the divided areas 23a to 23h are equal. The divided regions 23a to 23h are provided over the entire circumferential direction. Accordingly, each of the divided regions 23a to 23h has a sector shape with an inner angle corresponding to the center point of 45 °. The center point of the delay element 23 is disposed on the optical axis. Further, the transparent plate of the delay element 23 is arranged orthogonal to the optical axis.

  Each of the divided regions 23a to 23h delays the incident pulse laser beam. Therefore, the thickness of the transparent plate is different in each of the divided regions 23a to 23h. For example, the divided area 23a is the thinnest and the divided area 23h is the thickest. Then, the thickness increases in the order of the divided area 23a, the divided area 23b, the divided area 23c, the divided area 23d, the divided area 23e, the divided area 23f, the divided area 23g, and the divided area 23h. Therefore, the plate thickness of the transparent plate changes so that the transparent plate of the delay element 23 has a spiral staircase shape. Furthermore, in each divided area, the plate thickness difference between adjacent divided areas is constant. Here, it is assumed that the transparent plate is formed of a crystal having a refractive index of 1.5. Between different regions, the pulse laser beam is delayed by an amount obtained by multiplying the difference in refractive index between the transparent plate and the medium (air) by the plate thickness difference. Thus, the plate thickness of the delay element 23 differs depending on the position. Therefore, the pulse laser beam is given a time delay according to the incident position. The pulsed light from the divided regions 23b to 23h is given a time delay based on the plate thickness difference based on the pulsed light from the divided region 23a. That is, the divided areas 23b to 23 are delayed from the divided area 23a.

  The delay given to the pulse laser beam is as shown in FIG. FIG. 4 shows the waveform of the pulsed light after passing through the divided area. In FIG. 4B, in order from the top, pulse light having a delay time of 0 (pulse light having passed through the divided region 24a), pulse light having the next smallest delay time (pulse light having passed through the divided region 24b), and The pulse light with the longest delay time (pulse light that has passed through the divided region 24h) is shown. In FIG. 4B, the horizontal axis represents time, and the vertical axis represents pulsed light intensity. In FIG. 4B, the right side is the leading side of the pulse and the left side is the rear side of the pulse.

  The delay time between the pulsed lights that have passed through the adjacent divided areas is defined as a reference delay time Δt. For example, the pulsed light that has passed through the divided region 23b is delayed by the reference delay time Δt than the pulsed light that has passed through the divided region 23a. As described above, the reference delay time Δt corresponds to a value obtained by multiplying the difference in refractive index by the difference in plate thickness between adjacent divided regions. Further, since eight divided regions are provided, the pulsed light that has passed through the divided region 24h is delayed by seven times the reference delay time Δt than the pulsed light that has passed through the divided region 23a. When the pulsed light from the divided region 23a is used as a reference, the delay time of the pulsed light that has passed through the divided region 23c is 2 × Δt, the delay time of the pulsed light that has passed through the divided region 23d is 3 × Δt, and the divided region 23e is The delay time of the pulsed light that has passed is 4 × Δt, the delay time of the pulsed light that has passed through the divided region 23f is 5 × Δt, and the delay time of the pulsed light that has passed through the divided region 23g is 6 × Δt. Therefore, the pulsed light from the divided area 23a is on the most front side, and the pulsed light from the divided area 23h is on the most rear side.

  The pulsed light from each divided region is sequentially delayed in accordance with the thickness of the incident divided region. There is a time lag in the pulsed light from the adjacent divided region by the reference delay time Δt. This reference delay time Δt is shorter than the pulse width of the pulse laser beam. Further, the reference delay time Δt is about the same as the bunch length of the electron beam 31 to be monitored. More precisely, the reference delay time Δt is longer than the bunch length. For example, the reference delay time Δt is set to the bunch length in consideration of the jitter of the pulse laser beam and the electron beam. Therefore, the reference delay time Δt is longer than the bunch length by at least the jitter of the pulse laser beam and the electron beam. Accordingly, the pulsed light from each divided region propagates with a deviation of the bunch length or more. Depending on the position on the XY plane, the timing of the leading and trailing ends of each pulsed light is shifted.

  Here, the pulsed light that has passed through the divided region 23h with the longest delay time and the pulsed light that has passed through the divided region 23a with the zero delay time partially overlap in time. A period in which the pulsed light that has passed through the divided area 23h and the pulsed light that has passed through the divided area 23a overlap is defined as an overlapping period T. Here, the width of the overlap period T is longer than the bunch length of the electron beam. The overlap period T is set, for example, in consideration of jitter between the pulse laser beam and the electron beam in the bunch length. Therefore, the overlap period T is longer than the bunch length by the amount of jitter between the pulse laser beam and the electron beam. In the overlapping period T, the pulsed laser light overlaps over the entire outer periphery of the optical axis of the pulsed laser light in terms of time. For this reason, the maximum delay time by the delay element 23 is made shorter than the pulse width of the pulse laser beam. Therefore, 7 × Δt is shorter than the pulse width.

  Therefore, in the slice of the pulse laser beam in the overlap period T, the pulse laser beam exists in all directions centered on the optical axis. That is, at an arbitrary timing within the overlap period T, pulsed light is emitted from all the divided regions. In other words, at a timing outside the overlap period T, there is a divided region where pulse light is not emitted from one or more divided regions and pulse light is not emitted. A part of this overlap period T is used for measuring the electron beam. Specifically, the timing at which the light included in the overlapping period T passes through the electro-optical element 30 is matched with the timing at which the bunch passes through the electro-optical element 30. At the timing when the bunch passes through the electro-optical element 30, the light within the overlapping period T passes through the electro-optical element 30. When the bunch passes through the electro-optical element 30, it is preferable that light included in the overlapping period T is always passed through the electro-optical element 30. In this case, while the bunch passes through the electro-optic element 30, the pulsed light is incident on all the divided regions 23a to 23h.

  Further, in the slice of the pulse laser beam in the overlap period T, the wavelength is shifted in each divided region. As described above, the wavelength of the pulse laser beam from the light source unit 10 changes linearly with respect to time. For this reason, when the pulse laser beam passes through the delay element 23 that gives a delay time according to the incident position, the wavelengths at the same timing are different. For example, the pulse laser light from the divided region 23a and the pulse laser light from the divided region 23b have different wavelengths at the same timing according to the reference delay time Δt. Furthermore, in the slice of the pulsed laser light in the overlapping period T, the wavelengths of the pulsed light emitted from the divided regions 23a to 23h are sequentially shifted. At the same timing, the pulsed light emitted from the divided regions 23a to 23h has different wavelengths. In the slice of the pulse laser beam in the overlapping period T, light having different wavelengths is emitted from the divided regions 23a to 23h. The wavelength gradually shifts with time. At the same timing, there is a wavelength distribution in the XY plane. At the same timing, the wavelength changes for each divided region.

Within the overlap period T, the wavelength of the light emitted from each of the divided regions 23a to 23h varies with time. For example, the wavelength of light that passes through each of the divided regions 23a to 23h within the overlapping period T becomes shorter as time passes. Here, the wavelengths at both ends of the overlap period T are considered. First, as shown in FIG. 4B, the wavelength of light from the divided region 23a at the leading end of the overlapping period T is _λaL . Similarly, the wavelength of light from the divided region 23a at the end on the rear side of the overlap period T is λ _aS . Therefore, within the overlapping period T, the wavelength of light passing through the divided region 23a increases linearly from λ _aL to λ _aS as time elapses. Note that λ _aS is equal to the shortest wavelength λ _{S of the} entire pulsed laser beam. Similarly, the wavelength of light from divided regions 23b at the edge of the top side of the overlap period T and lambda _bL, the wavelength of light from divided regions 23b at the rear end of the overlap period T and lambda _bS. Further, the wavelength of the light from the divided region 23h at the leading end of the overlap period T is λ _hL . Similarly, the wavelength of light from the divided region 23h at the rear end of the overlap period T is _λhS . Note that λ _hL is equal to the longest wavelength λ _{L of the} entire pulsed laser beam. Further, λ _aS and λ _bS are shifted by a wavelength corresponding to the reference delay time Δt. Similarly, λ _aL and λ _bL are shifted by a wavelength corresponding to the reference delay time Δt.

Although not shown in FIG. 4B, for the divided regions 23c to 23g, the wavelengths at the leading end in the overlap period T are λ _cL , λ _dL , λ _eL , λ _fL , and λ _gL , respectively. And λ _cS , λ _dS , λ _eS , λ _fS , and λ _gS respectively. Here, in the whole pulse laser beam, the pulse front end has the longest wavelength λ _L and the pulse rear end has the shortest wavelength λ _S. Then, the wavelength of the pulse laser beam changes linearly with respect to time. Therefore, λ _aL <λ _bL <λ _cL <λ _dL <λ _eL <λ _fL <λ _gL <λ _hL . In addition, the _{λ aS <λ bS <λ cS} <λ dS <λ eS <λ fS <λ gS <λ hS. Thus, the wavelength of the light emitted in the overlap period T is longer in the divided region with a longer delay time. That is, as the divided region has a longer delay time, the pulsed light included in the overlapping period T has a wavelength (long wavelength) on the head side of the pulsed laser light.

Here, for example, the reference delay time Δt is set longer than the overlap period T. Then, λ _aL than λ _bs, becomes shorter. Therefore, the wavelength range λ _{aL to} λ _aS of the light emitted from the divided region 23a does not overlap with the wavelength range λ _{bL to} λ _{bS of} the light emitted from the divided region 23b. That is, the wavelength ranges λ _{aL to} λ _aS and the wavelength ranges λ _{bL to} λ _bS are completely deviated. Thus, in the overlap period T, the wavelength range of light emitted from any one divided region does not overlap with the wavelength range of light emitted from the other seven divided regions. In the overlap period T, the wavelength range of light emitted from one divided region is completely deviated from the wavelength range of light emitted from the other seven divided regions. Within the overlapping period T, the wavelength of the light emitted from any one divided region is not emitted from the other seven divided regions.

  In the above description, the wavelength range is not overlapped in the entire overlap period T. However, the present invention is not limited to this. That is, it is only necessary that the wavelength ranges emitted from the divided regions do not overlap while the bunch passes through the electro-optic element 30. Therefore, while the bunch passes through the electro-optical element 30, the wavelength of light emitted from any one divided region is not emitted from the other seven divided regions. That is, while the bunch does not pass through the electro-optic element 30, light of that wavelength is emitted from the other seven divided regions. Thus, while the bunch passes through the electro-optic element 30, the wavelength of the light emitted from each divided region is completely shifted. Note that the pulse width of the entire pulse laser beam emitted from the light source unit 10 takes into account the number of divisions, the pulse overlap period T, and the reference delay time Δt. For example, when eight divided regions 23a to 23h are provided, it is preferable to set the pulse width to 10 times or more the bunch length.

  Thus, the plate thickness of the delay element 23 changes according to the position in the XY plane. That is, the optical path length changes according to the position on the XY plane. Thereby, the pulse laser beam is delayed according to the position in the XY plane. That is, the position of the pulsed light from each divided region is shifted in the Z direction. For this reason, the pulse width of the pulse laser beam is extended. Here, the front end surface of the pulse laser beam has a spiral staircase shape. As the delay element 23, a liquid crystal element in which liquid crystal is sandwiched between a pair of transparent substrates can be used. And you may change the voltage applied to a liquid crystal according to a position. In addition, a material in which a transparent phase shift film is formed on a transparent substrate, such as a phase shift mask, can be used as the delay element 23. Further, a reflective delay element may be used. In this case, a spiral step-like mirror can be used as the delay element 23.

  The pulsed laser light from the delay element 23 enters the polarization conversion element 24. The polarization conversion element 24 converts the polarization state according to the incident position. For example, the polarization conversion element 24 converts linearly polarized light into radial radial polarized light. As the polarization conversion element 24, for example, Zpol manufactured by Nanophoton Corporation can be used. Here, a broadband Zpol is used as the polarization conversion element 24. The configuration of the polarization conversion element 24 will be described with reference to FIG. FIG. 5A is a diagram for explaining the polarization state before and after passing through the polarization conversion element 24. FIG. 5B is a plan view schematically showing the configuration of the polarization conversion element 24. FIG. 5C is a plan view for explaining the polarization state of the pulsed laser light that has passed through the polarization conversion element 24. In FIG. 5A, the pulse laser beam propagates in the + Z direction. For this reason, the pulse laser beam passes through the polarization conversion element 24 from the right side to the left side.

  First, the configuration of the polarization conversion element 24 will be described with reference to FIG. The polarization conversion element 24 is formed from a regular octagonal thin plate. The polarization conversion element 24 is formed, for example, by providing a wave plate on a transparent substrate made of glass or the like. Alternatively, the polarization conversion element 24 is formed by holding the wavelength plate with a holder. The polarization conversion element 24 has eight regions divided radially. As shown in FIG. 5B, these eight areas are defined as a divided area 24a to a divided area 24h. That is, the polarization conversion element 24 includes eight divided regions 24a to 24h. Here, the divided area 24a is arranged on the upper side, and the divided area 24b, the divided area 24c, the divided area 24d, the divided area 24e, the divided area 24f, the divided area 24g, and the divided area 24h are arranged in the clockwise order. . The divided areas 24a to 24f are arranged symmetrically with respect to the center point. Therefore, the eight divided regions 24a to 24h are arranged radially. In this way, the eight regions divided radially are divided regions 24a to 24h. The size of each divided area is equal. The divided regions 24a to 24h are provided over the entire circumferential direction. Accordingly, each of the divided regions 24a to 24h is an isosceles triangle having an inner angle of 45 ° corresponding to the center point.

  Here, the divided regions 24 a to 24 h provided in the polarization conversion element 24 correspond to the divided regions 23 a to 23 h provided in the delay element 23. That is, in the XY plane, the divided area 23a of the delay element 23 and the divided area 24a of the polarization conversion element 24 substantially coincide with each other. That is, when the alphabets a to h attached after the reference numerals are the same, the positions on the XY plane of the divided areas 23a to 23h and the divided areas 24a to 24h are the same. Since the pulsed laser light has a parallel light speed, the pulsed light emitted from the divided region 23a is incident on the divided region 24a. Similarly, the pulsed light from the divided area 23b is incident on the divided area 24b. Of course, the pulsed light from the divided regions 23c to 23h is also incident on the corresponding divided regions 24c to 24h, respectively. Therefore, the delay element 23 delays the pulsed laser light in a stepwise manner according to the incident position so as to correspond to the plurality of divided regions 24 a to 24 h provided in the polarization conversion element 24. Then, it is preferable that the delay time given stepwise by the delay element 23 is longer than the bunch length.

  In the divided regions 24a to 24h, half-wave plates having optical axes in different directions are provided. That is, the vibration direction of light is different for each of the divided regions 24a to 24h. In FIG. 5B, the optical axes in the divided regions 24a to 24h are indicated by arrows. Here, the optical axis of each divided region is shifted by 22.5 ° from the optical axis of the adjacent divided region. That is, with reference to the direction of the Y axis, as shown in FIG. 5B, the angle of the optical axis of the wave plate in the divided region 24a is 0 °, and the optical axis of the divided region 23b is 22.5 °. The optical axis of the divided region 24c is 45 °, the optical axis of the divided region 23d is 67.5 °, the optical axis of the divided region 24e is 90 °, and the optical axis of the divided region 23f is −67.5 °. Thus, the optical axis of the divided region 24g is −45 °, and the optical axis of the divided region 23h is −22.5 °. The optical axis is inclined by 22.5 ° in the order of the divided area 24a, the divided area 24b, the divided area 24c, the divided area 24d, the divided area 24e, the divided area 24f, the divided area 24g, and the divided area 24h.

  Accordingly, the optical axes of the pair of wave plates provided in the divided regions facing each other with respect to the center point are orthogonal to each other. For example, the optical axis of the divided area 24a is 0 °, and the optical axis of the divided area 24e facing the divided area 24a is 90 °. Similarly, the optical axis of the divided region 24c and the optical axis of the divided region 24g are orthogonal to each other. In other words, in the pair of wave plates provided in the divided regions facing each other, the difference in the angle of the optical axis is 90 °. As described above, the pair of divided regions arranged diagonally across the center points of the divided regions 24a to 24h are provided with wave plates having different optical axes by 90 °.

  The half-wave plate emits incident light with a half-wave phase difference. Therefore, if the angle formed by the azimuth (polarization axis) of the linearly polarized light with respect to the optical axis of the half-wave plate is θ, the light passing through the half-wave plate is a straight line rotated by 2θ from the original linearly polarized light. It becomes polarized light. For example, when the optical axis of the half-wave plate and the polarization axis of linearly polarized light are shifted by 45 °, the half-wave plate emits linearly polarized light whose polarization axis is shifted by 90 °. The polarization axis of linearly polarized light is the direction of the vibration plane of the electric vector in the XY plane.

  Here, linearly polarized light having a polarization axis along the Y direction is incident from the light source unit 10. In other words, the optical axis of the divided region 24a coincides with the polarization axis of the P-polarized incident light. As shown in FIG. 5A, the polarization conversion element 24 is arranged on the optical path. Then, a phase shift occurs between the light transmitted through the upper divided region 24a and the light transmitted through the lower divided region 24e. That is, the phase of light is shifted by 180 ° between the divided region 24a and the divided region 24e that are arranged facing each other vertically. Assuming that linearly polarized light is output from the light source unit 10, the phases of the orthogonal components of the electric vectors match before passing through the polarization conversion element 24. When linearly polarized light passes through the polarization conversion element 24, the phase of the electric vector is shifted by 180 ° between the divided region 24a and the divided region 24e. That is, the vibration direction of the electric vector is opposite between the upper divided region 24a and the lower divided region 24e. In the upper divided region 24a and the lower divided region 24e, the polarization directions are opposite to each other. The light transmitted through the upper divided region 24a and the light transmitted through the lower divided region 24e are linearly polarized light on the same straight line (straight line parallel to the Y axis), but their vibration directions are opposite.

  Here, linearly polarized light whose polarization axis is in the Y direction is incident on the polarization conversion element 24. That is, the optical axis of the divided region 24a and the polarization axis of the incident light coincide. As shown in FIG. 5A, the polarization state of the pulsed light that has passed through the divided region 24a does not change because the plane of polarization (the vibration plane of the electric vector) coincides with the optical axis. That is, the linearly polarized light in the Y direction remains. On the other hand, the polarization state of the pulsed light that has passed through the divided region 24e changes because the plane of polarization is orthogonal to the optical axis. That is, the direction of vibration of the pulsed light from the divided region 24e is opposite to that of the pulsed light from the divided region 24a. Here, since the optical axis and the polarization axis are shifted by 90 °, the polarization axis rotates 180 °. On the other hand, when the linearly polarized pulsed light passes through the divided region 24c, the polarization plane of the linearly polarized light changes by 90 °. That is, the divided region 24c having the optical axis inclined by 45 ° rotates the polarization axis by 90 °. Further, when the linearly polarized pulsed light passes through the divided region 24g, the plane of polarization of the linearly polarized light changes by −90 ° and is emitted. That is, the divided region 24c having the optical axis inclined by −45 ° rotates the polarization axis by −90 °. In this way, the polarization conversion element 24 delays light by a different phase depending on the incident position. Thereby, the polarization plane rotates in the XY plane.

  When linearly polarized pulsed laser light passes through the polarization conversion element 24, the polarization state is as shown in FIG. That is, the polarization conversion element 24 converts linearly polarized light into radial polarized light whose polarization axis is radial. Precisely, when a linearly polarized laser beam is incident on the polarization conversion element 24, a polarization state close to radial polarization is obtained. Here, as shown in FIG. 5C, a region corresponding to the divided region 24a is defined as a region A in the cross section obtained by slicing the pulsed laser light in the XY direction. An area corresponding to the divided area 24b is referred to as an area B. Similarly, the areas corresponding to the divided areas 24c to 24h are referred to as areas C to H, respectively. Thus, the vibration directions of the electric vectors are different in the regions A to H divided into eight fan shapes. The pseudo-radial polarized light is divided into 8 regions A to H.

  The polarization axes of linearly polarized light emitted from a pair of divided regions facing the center point are parallel to each other. And a vibration direction is opposite in a pair of division area which opposes. Further, the polarization axis of the light emitted from the adjacent divided regions is shifted by 45 °. For example, the polarization plane of the light emitted from the divided region 24a and the divided region 24e is 0 °. Therefore, the polarization axes of the light in the regions A and E are parallel to the Y direction. The polarization axis of the light emitted from the divided region 24b and the divided region 24f is 45 °. The polarization axis of the light emitted from the divided region 24c and the divided region 24g is 90 °. Therefore, the polarization planes of the light in the regions C and G are parallel to the X direction. Further, the polarization axis of the light emitted from the divided regions 24d and 24h is −45 °. Therefore, the angle of the polarization axis changes according to the incident position, and the outgoing polarization displacement becomes radial. In this way, the polarization conversion element 24 changes the polarization state of the incident light in accordance with the incident position, and performs control so that the desired polarization state is obtained.

  By making linearly polarized light incident on the polarization conversion element 24, it is possible to control the polarization state to be close to radial polarization. Specifically, the optical axis of the laser beam and the center point of the polarization conversion element 24 are matched. Further, the polarization conversion element 24 is disposed orthogonal to the optical axis. Then, the optical axis of the divided region 24a is matched with the polarization axis of the linearly polarized light. In this way, linearly polarized light can be changed to pseudo radial polarized light that approximates radial polarized light. In addition, when the linearly polarized light whose polarization axis is in the X direction is incident on the polarization conversion element 24, the polarization axis has a shape close to a circle. That is, the linearly polarized light changes to pseudo azimuth polarized light that is close to azimuth polarized light. In the above description, the eight-divided polarization conversion element 24 has been described, but the number of divisions is not limited thereto. For example, a 16-part or 4-part polarization conversion element 24 may be used. More detailed measurement can be performed by increasing the number of divisions. From the polarization conversion element 24, a radial polarization state in which the direction of the polarization plane in the XY plane is radial is generated.

  Note that pulsed laser light delayed by the delay element 23 is incident on the polarization conversion element 24. For this reason, the pulsed light incident on the divided regions 24 a to 24 h of the polarization conversion element 24 is shifted in time as shown in FIG. Therefore, at the first timing, the pulsed light is incident only on the divided region 24a. At the next timing, the pulsed light is incident only on the divided regions 24a and 24b. In this way, the number of divided areas in which pulsed light is incident in order increases. In the overlap period T, pulsed light enters all the divided regions 24a to 24h. After the overlapping period, the pulsed light does not enter the divided region 24a. At the next timing, the pulsed light does not enter the divided regions 24a and 24b. Then, the divided areas where the pulsed light does not enter gradually increase. In other words, the divided area into which the pulsed light changes changes with time. Accordingly, the divided area where the pulsed light is incident changes with time.

  The pulse laser beam emitted from the polarization conversion element 24 enters the mirror 25. The mirror 25 is disposed in the beam path of the electron beam 31. The mirror 25 is inclined 45 ° with respect to the optical axis of the laser beam. Accordingly, the mirror 25 reflects the laser light in the direction of the electro-optical element 30. Laser light from the mirror 25 enters the electro-optic element 30. Further, the pulse laser beam reflected by the mirror 25 propagates in the direction opposite to the traveling direction of the electron beam 31. That is, the pulse laser beam is reflected by the mirror 25 so as to travel toward the upstream side of the electron beam 31.

  The mirror 25 has a hollow shape with a central portion cut out. Further, the laser light is formed in a ring shape by the axicon lenses 21 and 22. For this reason, even when the hollow mirror 25 is used, most of the laser light is incident on the electro-optic element 30. In other words, the mirror 25 has a hollow portion corresponding to the ring-shaped laser beam. Therefore, the annular laser beam does not enter the hollow portion of the mirror 25. Thereby, most of the laser light is incident on the electro-optical element 30. Accordingly, it is possible to prevent a decrease in the utilization efficiency of the laser beam and to perform accurate measurement. Further, the electron beam 31 passes through the hollow portion of the mirror 25. Thereby, an electron beam can be measured nondestructively.

  The mirror 25 is arranged in the path of the electron beam 31. Therefore, the mirror 25 existing in the path of the electron beam 31 is arranged in a vacuum. That is, the mirror 25 is disposed in the vacuum chamber. Accordingly, the pulsed laser light from the polarization conversion element 24 is incident on the mirror 25 through the window provided in the vacuum chamber. Thus, the delay element 23 and the polarization conversion element 24 are disposed in the atmosphere. Thereby, most of the incident optical system 20 can be installed in the atmosphere, and the optical system can be easily adjusted. Therefore, convenience can be improved.

  The pulsed laser light reflected by the mirror 25 enters the electro-optic element 30. That is, the pulse laser beam emitted from the incident optical system 20 passes through the electro-optic element 30 disposed in the path of the electron beam 31. At this time, the timing at which the pulse laser beam passes through the electro-optic element 30 and the timing at which the electron beam 31 passes through the electro-optic element 30 are synchronized. That is, the pulse laser beam and the bunch of the electron beam 31 pass through the electro-optic element 30 at the same timing. Further, the pulse laser beam and the electron beam 31 pass through the electro-optic element 30 from opposite directions. That is, the propagation direction of the pulse laser beam and the traveling direction of the electron beam 31 are parallel and opposite to each other. For example, when the pulse laser beam propagates in the + Z direction, the electron beam 31 travels in the −Z direction. Further, the optical axis of the pulse laser beam and the center position of the electron beam 31 on the XY plane are substantially coincident.

  Here, the electro-optical element 30 will be described with reference to FIGS. 6 and 7. FIG. 6A is a perspective view showing a state in which the electron beam 31 and the pulse laser beam pass through the electro-optic element 30. FIG. 6B is a plan view showing the configuration of the electro-optic element 30. FIG. 7 is a side view conceptually showing a state in which the bunch 37 of the electron beam 31 and the pulse laser beam pass through the electro-optic element 30. The electro-optic element 30 is composed of an electro-optic crystal having a predetermined thickness. The thickness of the electro-optic element 30 is preferably shorter than the spatial bunch length. Here, the thickness of the electro-optical element 30 can be set to 0.01 mm to 0.1 mm, for example.

  As shown in FIG. 6B, the electro-optical element 30 is formed in a ring shape. That is, the outer shape of the electro-optic element 30 is circular. A circular hollow portion 33 is provided at the center of the electro-optic element 30. The hollow portion 33 is an empty space. The electron beam 31 passes through the hollow portion 33. That is, the hollow portion 33 is larger than the lateral shape of the electron beam 31. Therefore, the size of the hollow portion 33 is determined according to the assumed shape of the bunch in the lateral direction. As a result, the electron beam 31 does not enter the crystal portion of the electro-optic element 30. Therefore, measurement can be performed without destroying the electron beam.

  Further, the pulse laser beam is formed into an annular shape by an axicon lens. That is, the shape of the pulse laser beam on the XY plane is a donut shape. The annular pulse laser beam is incident on the electro-optic element 30. Accordingly, the annular pulse laser beam is incident on the outer portion of the hollow portion 33 and inside the outer shape of the electro-optic element 30. That is, the annular pulse laser beam passes through the electro-optic crystal of the electro-optic element 30 without passing through the hollow portion 33. The ring-shaped pulse laser beam passes through the electro-optical element 30 so as to surround the outer periphery of the electron beam 31.

  Here, as shown in FIG. 6B, the electro-optic element 30 has a divided region radially divided into eight. Eight divided regions provided in the electro-optic element 30 are defined as divided regions 30a to 30h. As shown in FIG. 6B, the electro-optic element 30 has eight divided regions 30a to 30h. In FIG. 6B, the divided areas 30a to 30h are arranged along the circumferential direction. The divided areas 30a to 30h are arranged radially. The sizes of the divided areas 30a to 30h are equal. The divided areas 30a to 30h are provided over the entire circumferential direction. The divided areas 30a to 30h are arranged at regular intervals in the circumferential direction. Accordingly, each of the divided regions 30a to 30h has a sector shape with an inner angle corresponding to the center point of 45 °. In addition, the fan-shaped center side is hollow. The center of the hollow portion 33 of the electro-optic element 30 is disposed on the optical axis. Further, the electro-optical element 30 is disposed orthogonal to the optical axis. Each of the divided regions 30a to 30h is provided with a transparent electro-optic crystal such as ZnTe (zinc telluride), LiNbO3 (lithium niobate), or BBO. In addition to these inorganic crystals, an organic polymer film having a quick response may be used. Here, the electro-optic crystals used in the divided regions 30a to 30h have the same configuration in directions other than the crystal axis.

  The crystal axis orientations of the respective divided regions 30a to 30h are indicated by dotted arrows in FIG. In FIG. 6B, the (001) crystal axis direction is indicated by a dotted arrow. In each divided region 30a to 30h, the direction of the crystal axis is different. Specifically, the crystal axes of the electro-optic element 30 are arranged radially. When the eight crystal axes are extended, they intersect at one point on the optical axis. Thus, the divided regions 30a to 30h are each provided with an electro-optic crystal. The electro-optic crystals provided in the respective divided regions 30a to 30h have crystal axes in different directions.

  As described above, the electro-optic element 30 is provided with the divided regions 30a to 30h divided into eight equal parts. For this reason, each divided region 30a-30h has a 45 ° fan shape. In adjacent divided regions, the optical axes of the electro-optic crystals are in different directions. Here, since eight electro-optic crystals are provided, the angle formed by the crystal axes of adjacent divided regions is 45 °. A plurality of electro-optic crystals are arranged along the circumferential direction so as to be shifted by 45 ° from the crystal axis of the adjacent divided region. Therefore, if the crystal axis of the divided region 30a is 0 °, the crystal axis of the divided region 30c is 90 °.

  The divided areas 30a to 30h provided in the electro-optic element 30 correspond to the areas A to H, respectively. Therefore, in the XY plane, the positions of the divided area 23a, the divided area 24a, and the divided area 30a substantially coincide. The pulsed light emitted from the divided area 24a is reflected by the mirror 25 and enters the divided area 30a. Furthermore, the pulsed light emitted from the divided area 23a enters the divided area 30a via the divided area 24a. Similarly, the divided areas 30b to 30h correspond to the divided areas 24b to 24h. That is, pulsed light from the divided areas 24a to 24h with the same alphabet is incident on the divided areas 30a to 30h. For example, the pulsed light from the divided region 24b is incident on the divided region 30b.

  Thus, the light of each area | region AH enters into corresponding division area 30a-30h. Here, the polarization conversion element 24 converts linearly polarized light into radial radial polarized light. That is, the polarization conversion element 24 emits a pulse laser beam in a radial polarization state. Furthermore, the crystal axes of the electro-optic element 30 are arranged radially. Therefore, the crystal axis of the electro-optic element 30 and the polarization plane of the pulse laser beam are in the same direction. In all the divided regions 30a to 30h of the electro-optic element 30, the vibration plane of the electric vector of the incident pulse light coincides with the crystal axis direction. For example, the crystal axis in the divided region 30a of the electro-optic element 30 is in the Y direction, and the polarization axis of the pulsed light emitted from the divided region 24a in the polarization conversion element 24 is in the Y direction. Of course, in the other divided regions 30b to 30h, the polarization axis is parallel to the crystal axis. Thus, although it is radial polarization as a whole, linearly polarized light parallel to the crystal axis is incident on each of the divided regions 30a to 30h.

  The refractive index of the electro-optic crystal changes depending on the electric field. For example, when an electric field parallel to the crystal axis is applied, the refractive index in the crystal axis direction changes. In the Pockels element, the refractive index changes in proportion to the electric field strength. At this time, in the XY plane, the refractive index does not substantially change in the direction perpendicular to the crystal axis. Therefore, in the electro-optic crystal, the refractive index changes in proportion to the electric field strength, and birefringence is induced.

  The pulse laser beam in the radial polarization state is incident on such an electro-optical element 30 as shown in FIG. Here, for example, it is assumed that a radial electric field is applied to the electro-optic element 30. In this case, the equipotential lines are concentric. Note that the center of the radial electric field coincides with the center of the hollow portion 33. An electric field parallel to each crystal axis is applied to the electro-optic element 30. A phase change occurs due to the birefringence induced by the electric field. When birefringence occurs, the polarization state changes to become elliptically polarized light. That is, the linearly polarized light is rotated and converted into elliptically polarized light. When a radial electric field is applied, the pulsed light emitted from each divided region 30a-30h becomes elliptically polarized light. In addition, the inclination of elliptically polarized light changes according to the electric field strength. That is, the inclination of elliptically polarized light in the XY plane changes depending on the electric field strength. Thus, elliptically polarized light corresponding to the electric field intensity is emitted from each of the divided regions 30a to 30h. Accordingly, the pulse laser beam that has passed through the electro-optic element 30 to which an electric field is applied is not a radial polarization as a whole. On the other hand, birefringence does not occur when no electric field is applied. For this reason, the pulse laser beam remains in the radial polarization state. That is, if no electric field is generated, the polarization state does not change before and after passing through the electro-optic element 30.

  As shown in FIG. 7, the bunch 37 and the pulse laser beam pass through the electro-optic element 30 at the same timing. FIG. 7 is a cross-sectional view of the electro-optical element 30 on the YZ plane, and schematically shows the bunch 37 and the pulsed light that pass through the electro-optical element 30. Further, in FIG. 7, the pulsed light that passes through the divided region 30a is referred to as pulsed light 35a, and the pulsed light that passes through the divided region 30h is referred to as pulsed light 35h. Therefore, the light in region A is pulsed light 35a, and the light in region H is pulsed light 35h.

  As shown in FIG. 7, the pulsed laser light passes through the electro-optical element 30 in synchronization with the bunch 37. Specifically, pulsed laser light enters the electro-optic crystal of the electro-optic element 30, and the bunch 37 enters the hollow portion 33 of the electro-optic element 30. The pulse laser beam is sufficiently longer than the bunch length. Furthermore, the overlap period T is longer than the bunch length. Accordingly, the bunch 37 always passes through the electro-optic element 30 during the period in which the pulse laser beam passes through the electro-optic element 30. Here, a period during which the bunch 37 passes is defined as a bunch passing period. The period when the bunch is not passing is defined as the bunch non-passing period. The bunch non-passing period is arranged on both sides of the bunch passing period. In FIG. 7, the bunch non-passing period and the bunch passing period move to the left side with time, and the overlapping period T moves to the right side with time. While the bunch passage period and the electro-optic element 30 overlap, the electro-optic element 30 is included in the overlap period T. Further, the pulse laser beam passes through the electro-optical element 30 even during a part of the overlap between the bunch non-passing period and the electro-optical element 30.

  Accordingly, an electric field is generated by charges (electrons) contained in the bunch of the electron beam 31 during the period in which the pulse laser beam passes through the electro-optic element 30. An electric field generated by the electric charge in the bunch is applied to the electro-optic element 30. Then, the electro-optic element 30 changes the polarization state of the pulsed laser light by birefringence. Specifically, each of the regions A to H is linearly polarized before passing through the electro-optic element 30, but becomes elliptically polarized after passing. Furthermore, the change in the polarization state changes depending on the electric field strength. Therefore, in the region where the electric field strength is strong, the polarization state changes from linearly polarized light. That is, since the birefringence effect increases in proportion to the electric field strength, the change in the polarization state increases in a region where the electric field strength is high. As described above, when the timing when the bunch passes through the electro-optic element 30 and the timing when the pulse laser beam passes through the electro-optic element 30 are synchronized, the polarization state changes from the radial polarization.

  Note that pulsed laser light delayed by the delay element 23 is incident on the electro-optic element 30. For this reason, the pulsed light incident on the divided regions 30a to 30h of the electro-optical element 30 is shifted in time as shown in FIG. Here, as shown in FIG. 7, the pulsed light 35a passing through the divided region 30a is advanced ahead of the pulsed light 35h passing through the divided region 30h.

  Further, at the first timing when the pulse laser beam passes through the electro-optic element 30, the pulse light 35a of the region A is incident only on the divided region 30a. When the time has elapsed by Δt, the pulsed light of the regions A and B is incident on the two divided regions 30a and 30b, respectively. In this way, the number of divided areas in which pulsed light is incident in order increases. In the overlap period T, the pulsed light enters all the divided regions 30a to 30h. In other words, in the overlap period T, the pulse laser beam is incident on the electro-optic element 30 in all directions around the optical axis of the pulse laser beam on the XY plane. In other words, in the XY plane, the pulsed laser light is incident on the electro-optical element 30 in the entire circumferential direction. Thereby, the entire outer periphery of the bunch 37 in the slice on the XY plane is surrounded by the pulse laser beam. Here, the outer shape of the pulse laser beam is a circle in a slice cross section perpendicular to the optical axis. In order to do this, the maximum delay time by the delay element 23 is made shorter than the pulse width of the pulse laser beam.

After the overlap period T, the pulsed light does not enter the divided region 30a. At the next timing, the pulsed light does not enter the divided regions 30a and 30b. Then, the divided areas where the pulsed light does not enter gradually increase. In other words, the divided area into which the pulsed light changes changes with time. Therefore, the divided areas where the pulsed light is incident are changed in order according to time. Further, the wavelength at the same timing is shifted for each region. Therefore, the pulsed light has a different wavelength for each of the regions A to H while the bunch passage period and the electro-optic element 30 overlap. For example, in the state shown in FIG. 7, the wavelength of the light passing through the divided region 30a of the electro-optic element 30 is λ _1, and the wavelength of the light passing through the divided region 30h of the electro-optic element 30 is λ ₈ . To do. In this case, λ ₁ is shorter than λ ₈ . Of course, in the other divided regions 30b to 30g, light of different wavelengths passes at the same timing. Actually, since the electro-optical element 30 has a finite thickness, the pulsed light incident on the electro-optical element 30 at a certain timing has a predetermined wavelength width. At this timing, the polarization state of light having a wavelength width corresponding to the thickness of the electro-optical element 30 changes.

  The electrons in the bunch 37 are accelerated to a relativistic region. Therefore, the electric field generated by the electrons in the bunch is in the horizontal direction. That is, an electric field is not generated in the traveling direction (Z direction) of the electron beam. The electric field lines of the electric field due to the electrons in the bunch are parallel to the XY plane. The electric field does not couple between adjacent slices. More precisely, an electric field is generated in a 1 / γ cone. Note that γ is an electron Lorentz factor. Therefore, when sufficiently high energy is applied to electrons, γ increases and the electric field strength in the Z direction can be ignored. For example, if the bunch contains a charge of 3.4 nC, the bunch width (FWHM) is 80 fsec, and the bunch length σz is about 12 μm (RMS), the distance from the center in the XY plane is 5 mm, and the horizontal direction An electric field of up to 400 MV / m is generated.

  When electrons have high energy, an electric field is applied to the electro-optic element 30 only during the bunch passage period. Accordingly, the polarization state of the pulse laser beam changes only while the bunch passage period overlaps with the electro-optic element 30. That is, while the bunch non-passing period overlaps with the electro-optic element 30, the polarization state of the pulse laser beam does not change substantially. In the bunch non-passing period, the light in the regions A to H remains linearly polarized and remains in the radial polarization state. In addition, while the bunch non-passing period overlaps with the electro-optic element 30, it may be outside the overlapping period T. Outside the overlap period T, no pulsed light is emitted from a part of the divided regions 30a to 30h. That is, it becomes radial polarized light in which a part of the regions A to H is lost. Note that in the overlap period T, in the bunch non-passing period, the pulsed laser light passes through the electro-optic element 30 with the radial polarization.

  Then, the pulse laser beam that has passed through the electro-optical element 30 enters the emission optical system 40. The emission optical system 40 is an optical system for propagating the pulsed laser light emitted from the electro-optic element 30 to the spectrometer 50. The exit optical system 40 includes a mirror 41, a polarization conversion element 42, a delay element 43, an axicon lens 44, an axicon lens 45, and a polarizer 46.

  The pulsed laser light that has passed through the electro-optic element 30 enters the mirror 41. Similar to the mirror 25, the mirror 41 has a hollow shape with a central portion cut out. Thereby, similarly to the mirror 25, non-destructive measurement is possible. Furthermore, pulsed laser light can be efficiently extracted from the path of the electron beam 31. The mirror 41 is disposed in the beam path of the electron beam 31. The mirror 41 is inclined 45 ° with respect to the optical axis of the laser beam. Therefore, the mirror 41 reflects the laser light in the direction of the polarization conversion element 42. Laser light from the mirror 41 enters the polarization conversion element 42.

  The mirror 25 is arranged in the path of the electron beam 31. Therefore, the mirror 25 existing in the path of the electron beam 31 is arranged in a vacuum. The mirror 25 is disposed in the vacuum chamber. Accordingly, the pulsed laser light reflected by the mirror 41 enters the polarization conversion element 42 through the window provided in the vacuum chamber. Thereby, the polarization conversion element 42, the delay element 43, etc. can be arrange | positioned in air | atmosphere. Most of the emission optical system 40 can be installed in the atmosphere, and the optical system can be easily adjusted. Therefore, convenience can be improved.

  The pulsed laser light reflected by the mirror 41 enters the polarization conversion element 42. The polarization conversion element 42 has the same configuration as the polarization conversion element 24. That is, the polarization conversion element 24 having the same configuration as that of FIG. Accordingly, Zpol manufactured by Nanophoton Co. can be used for the polarization conversion element 42. Note that the configuration of the polarization conversion element 24 is the same as that of the polarization conversion element 24, and therefore the description thereof is omitted in detail. The polarization conversion element 42 is arranged in the same manner as the polarization conversion element 24. That is, in the polarization conversion element 42 and the polarization conversion element 24, the divided areas corresponding to the area A are optical axes in the same direction.

  The polarization conversion element 42 converts the polarization state according to the incident position. When light in a radial polarization state enters the polarization conversion element 42, the polarization state is converted into linearly polarized light. For example, in FIG. 5A, pulsed laser light propagates in the −Z direction. That is, the pulse laser beam propagates from the right side to the left side in FIG. By passing the radially polarized light through the polarization conversion element 42, the pulsed laser light becomes linearly polarized light. That is, the polarization conversion element 42 returns the polarization state converted by the polarization conversion element 24 to the original polarization state. Therefore, the polarization conversion element 42 becomes a polarization state cancellation element that cancels the radial polarization state converted by the polarization conversion element 24.

  However, as described above, the polarization state of the pulse laser beam incident on the polarization conversion element 42 is changed from the radial polarization. That is, the polarization state changes due to the influence of the electro-optic crystal. Therefore, even if it passes through the polarization conversion element 42, the pulse laser beam does not return completely to the original radial polarization state. In other words, the pulsed laser light that has passed through the polarization conversion element 42 is changed from the radial polarization state by the amount that the polarization state is changed by the electro-optic element 30. Therefore, elliptically polarized pulsed light corresponding to the electric field generated by the bunch 37 is emitted from each of the regions A to H. When the electric field due to the bunch is not generated, that is, when the timing at which the bunch and the pulse laser beam are incident on the electro-optical element 30 is shifted, the pulse laser beam that passes through the polarization conversion element 42 is the original linearly polarized light. Return to.

  The pulsed laser light emitted from the polarization conversion element 42 enters the delay element 43. The delay element 43 has the same configuration as that of the delay element 23 shown in FIG. That is, the delay element 43 gives the pulse laser beam a delay according to the incident position. However, the arrangement of the delay element 43 is different from that of the delay element 23. Specifically, the delay element 43 is arranged so that the sum of the delay time given by the delay element 43 and the delay time given by the delay element 23 is equal in all areas A to H. Therefore, in the light of the region H corresponding to the divided region 23 h, the delay element 23 gives the longest delay time (7 × Δt), but the delay element 43 has a delay time of zero. In the light of the region A corresponding to the divided region 23a, the delay time is 0 in the delay element 23, but the longest delay time (7 × Δt) is given in the delay element 43. In the light of the region B corresponding to the divided region 23b, the delay element 23 is given a delay time Δt, and the delay element 43 is given a delay time (6 × Δt).

  Thus, the equal delay time (7 × Δt) is given to all the regions A to H by the delay element 23 and the delay element 43. Therefore, when passing through the delay element 43, the pulse width is shortened and returns to the original pulse width. That is, the pulse widths of the pulse laser light after passing through the delay element 43 and the pulse laser light before passing through the delay element 23 are substantially equal. As a result, the timing of the pulsed light is the same in all areas A to H. Thus, the delay element 43 eliminates the time delay caused by the delay element 23. That is, the time delay corresponding to the incident position given by the delay element 23 is eliminated. The delay element 43 is a delay canceling element that cancels the time delay caused by the delay element 23. For this reason, in the Z direction, the pulse lights of all the regions A to H are at the same position. For example, the tip of the pulsed light in region A and the tip of the pulsed light in region H are at the same position.

  The pulsed laser light that has passed through the delay element 43 is incident on a pair of axicon lenses 44 and 45. Similar to the axicon lenses 21 and 22, the axicon lenses 44 and 45 have a conical shape. The pulsed laser light is refracted by a pair of axicon lenses 21 and 22. Thereby, the cross section of the pulse laser beam is changed from a ring shape to a circle.

The pulsed laser light refracted by the axicon lens 45 enters the polarizer 46. The pulsed laser light is focused on the polarizer 46 by the axicon lens 45. The polarizer 46 extracts linearly polarized light having a predetermined polarization plane. For example, the polarizer 46 transmits P-polarized light and does not transmit S-polarized light. That is, the polarizer 46 extracts only the P-polarized light from the pulse laser beam. As the polarizer 46, a polarizing plate, a polarizing prism, or the like can be used. For example, a Glan-Thompson prism or a Wollaston prism can be used. For example, a DUV Glan-Thompson prism manufactured by Kogyo Giken can be used. The DUV Glan-Thompson prism has a high extinction ratio of 5: 1000000 and corresponds to a wide band of 180 to 2200 nm.
Some Glan-Thompson prisms are designed to intentionally cut the S-polarized light component. When such a Glan-Thompson prism is used as the polarizer 46, P-polarized light passes and S-polarized light does not pass. That is, the P-polarized component is extracted from the pulse laser beam. The extinction ratio of the polarizer 46 is preferably 100000: 1 or more, and more preferably about 1000000: 1. The polarizer 46 extracts light having a predetermined polarization plane. That is, a predetermined polarization component of the pulse laser beam is extracted. Here, a linearly polarized light component in the Y direction is extracted. That is, the polarization component oscillating in the Y direction passes through the polarizer 46, and the polarization component oscillating in the X direction does not pass through the polarizer 46.

  The light extracted by the polarizer 46 will be described with reference to FIG. FIG. 8 is a diagram for explaining the light extracted by the polarizer 46. FIG. 8A is a conceptual diagram showing the P-polarized component of the pulsed light 35a in the region A, and FIG. 8B is a conceptual diagram showing the S-polarized component of the pulsed light 35a in the region A. is there. FIG. 8C is a conceptual diagram showing the P-polarized component of the pulsed light 35h in the region H, and FIG. 8D is a conceptual diagram showing the S-polarized component of the pulsed light 35h in the region H. is there. In FIG. 8, the horizontal axis indicates the wavelength, and the vertical axis indicates the intensity of each polarization component. Therefore, FIG. 8 shows the spectra of the P-polarized component and the S-polarized component. Further, since the time delay between the regions is eliminated by the delay element 43, the horizontal axis can be regarded as time.

As described above, the polarization state changes only during the bunch passage period. Further, within the bunch passage period, the wavelength of light is shifted according to the regions A to H. Therefore, the wavelength of the light whose polarization state has been changed by the electro-optic element 30 differs from region to region. For example, the wavelength range of the pulsed light 35a in the region A in the overlap period T is λ _{aL to} λ _aS . After passing through the electro-optic element 30, the polarization state changes in a part of the wavelength range λ _{aL to} λ _aS . In other words, in the pulsed light 35a, the polarization state does not change outside the wavelength range λ _{aL to} λ _aS . Therefore, after passing through the polarization conversion element 42, only the P-polarized light component is present outside the wavelength range λ _{aL to} λ _aS . After passing through the electro-optic element 30, it changes to elliptically polarized light within the wavelength range λ _{aL to} λ _aS . For this reason, after passing through the polarization conversion element 42, the P-polarized light component and the S-polarized light component exist outside the wavelength range λ _{aL to} λ _aS .

Therefore, in the pulsed light 35a in the region A incident on the polarizer 46, the P-polarized component is as shown in FIG. 8A, and the S-polarized component is as shown in FIG. 8B. Here, the wavelength at which the S polarization component appears is included in the wavelength range λ _{aL to} λ _aS . As described above, the pulsed light 35a has an S-polarized component only in a part of wavelengths. The P-polarized component is constant outside the wavelength range λ _{aL to} λ _aS . Ideally, the sum of the P-polarized component and the S-polarized component is constant regardless of the wavelength.

Similarly, with respect to the pulsed light 35h in the region H, an S-polarized component exists only at a part of the wavelengths. The wavelength at which the S-polarized component exists is different from the region A. For example, the wavelength range of the pulsed light 35h regions H in the overlap period T is a lambda _hL to [lambda] _hS. Therefore, only in the wavelength range lambda _hL to [lambda] _hS, there are S-polarized light component. Although the regions B to G are not illustrated, the S polarization component exists only in some wavelengths in the regions B to G. And in each area | region AH, the wavelength in which an S polarization component exists does not overlap. That is, the wavelength at which the S-polarized component exists is completely different for each of the regions A to H.

  Here, the polarizer 46 passes only the P-polarized light component. For this reason, the S polarization component shown in FIGS. 8B and 8D is cut. That is, only the P-polarized component shown in FIGS. 8A and 8C is extracted by the polarizer 46. In the graph of the P polarization component in each of the regions A to H, a dent is generated at a different wavelength for each region. This dent corresponds to the S-polarized component. Therefore, the size of the recess changes according to the electric field generated by the electron group in the bunch 37. In other words, the intensity of the P-polarized component changes according to the spatial distribution of the lateral slice of electrons in the XY plane.

  The pulsed laser light that has passed through the polarizer 46 enters the spectrometer 50 as shown in FIG. In addition, since the time delay is eliminated by the delay element 43, the P-polarized light components in the entire region enter the spectroscopic instrument 50 at the same timing. That is, since there is no temporal shift in the pulsed light in each region, the pulsed light in all regions A to H is incident at the same time. The spectrometer 50 has a spectroscopic unit 51 and a detection unit 52.

  The spectroscopic unit 51 is a spectroscope (spectroscope) including spectroscopic elements such as a diffraction grating (grating) and a prism. The spectroscopic unit 51 spatially disperses the pulsed laser light incident through a slit or the like provided on the incident side according to the wavelength. In the case of the spectroscopic unit 51 using a reflective diffraction grating, an optical system such as a concave mirror that guides light from the incident slit to the spectroscopic element and a concave mirror that guides light dispersed by the spectroscopic element to the detection unit 52 is provided. ing. Of course, you may use the spectroscopy part 51 which has a structure other than the above. The pulsed laser light is dispersed by the spectroscopic unit 51 in a direction perpendicular to the direction of the entrance slit. That is, the spectroscopic unit 51 wavelength-disperses the emitted light in a direction perpendicular to the line-shaped opening of the entrance slit. The outgoing light split by the spectroscopic unit 51 enters the detection unit 52.

  The detection unit 52 is an area sensor (camera) in which light receiving elements are arranged in a matrix. Specifically, the detection unit 52 is a two-dimensional array photodetector such as a two-dimensional CCD camera or a CMOS camera in which light receiving pixels are arranged in an array. For example, the detection unit 52 may be an ultra-high resolution high-sensitivity camera such as Phantom V10.0 manufactured by Vision Research. Phantom V10.0 has, for example, 4.3M pixels. Further, when the amount of received light is low, it can be attached to the image intensifier on the camera. It is preferable to use an image intensifier with a short afterglow time. Thereby, the restriction | limiting of a repetition measurement is eased and the repetition frequency of a measurement can be made high. For example, it is preferable to use an image intensifier of DHT (Delft High-Tech) Co., and the phosphor screen material is P46. In addition, for example, spectral images (spectral imaging) may be measured using ImSpector manufactured by SPECTRAL IMAGEING, etc. (H. Tomisawa et. Al. “Spectographic aprot for the breast frequre br ir f br ed br ech ri fre c) "Applied Surface Science 235 (2004) 214-220). The spectrometer 50 has, for example, a PGP structure (Prism-Grating-Prism).

As a result of being split by the spectroscopic unit 51, light of different wavelengths enters different light receiving pixels. That is, the incident light receiving pixel is shifted according to the wavelength. Thereby, it is possible to measure the spectrum of the pulse laser beam. For example, the light with the longest wavelength λ ₁ is incident on the light receiving pixel on one end side of the light receiving pixel row, and the light with the shortest wavelength λ _s is incident on the light receiving pixel on the other end side. The incident light receiving pixels are different depending on the wavelength. Further, since the chirped pulse laser beam is used, the light receiving pixel array corresponds to the time in the pulse laser beam. Therefore, light at different timings in the pulse enters different light receiving pixels. For example, the light at the front end of the pulse is incident on a light receiving pixel on one end side of the light receiving pixel row, and the light at the rear end of the pulse is incident on a light receiving pixel on the other end of the light receiving pixel row. Then, the spectrum of one pulse is detected by one frame of the camera of the detection unit 52. That is, the spectrum of one pulse of the pulsed laser beam is acquired by one frame of the camera of the spectroscopic measuring instrument 50. Thereby, the spectral distribution of the pulse laser beam can be measured at high speed.

  Here, the pulse laser beam incident on the spectrometer 50 will be described with reference to FIG. FIG. 9 is a graph schematically showing the spectrum of the pulse laser beam. In the graph of FIG. 9, the horizontal direction indicates the wavelength, and the vertical direction indicates the intensity of the pulsed laser beam. The intensity of the pulse laser beam in FIG. 9 is the intensity of the P-polarized component. In addition, after the light is split by the spectroscopic unit 51, the horizontal direction can be regarded as a spatial position on the camera light receiving surface of the detection unit 52. Furthermore, since the time delay between the regions is eliminated by the delay element 43, the horizontal direction can be taken as the time axis. The spectrum of FIG. 9 is measured in one frame of the camera.

  The P-polarized components in the respective regions A to H are added and are incident on the spectrometer 50. The light passing through the electro-optic element 30 in synchronization with the bunch 37 is developed in different wavelength ranges depending on the region. The pulsed light passing through the electro-optical element 30 in a state where an electric field from electrons is applied has a different wavelength for each region. For this reason, the wavelength range in which the dent corresponding to the S-polarized component exists is shifted for each of the regions A to H. Accordingly, the spectrum of the pulsed laser light incident on the spectrophotometer 50 has eight dents. Each dent corresponds to a dent in the spectrum of each region AH. This dent corresponds to the S-polarized component shaved by the polarizer 46. For example, the rightmost dent of the spectrum shown in FIG. 9 corresponds to the S-polarized component of the pulsed light in region A.

The rightmost recess is included in the wavelength range λ _{aL to} λ _aS . The leftmost dent corresponds to the S-polarized component of the pulsed light in region H. Thus, the leftmost indentations are included in the wavelength range λ _hL ~λ _hS. Similarly, the spectrum has dents corresponding to the S-polarized components in the regions B to G. Each dent appears at a different wavelength. And all the dents do not overlap with other dents. The dents in the different areas are shifted by a wavelength corresponding to the reference delay time Δt. That is, the respective recesses are separated in time. When the light is split by the spectroscopic unit 51, the respective recesses are developed at different wavelengths. The light of the wavelength corresponding to eight dents injects into the different position of a camera light-receiving surface. Therefore, P-polarized light components having wavelengths corresponding to the eight depressions are detected by different light receiving pixels.

  One recess corresponds to the electric field of one divided region. That is, the shape of the dent changes according to the electric field of each of the divided regions 30a to 30h. The shape of the dent corresponds to the change in the electric field of each slice with a time resolution corresponding to the time response of the electro-optic element. For example, the rightmost dent changes according to the electric field in region A. As the number of electrons increases, the electric field strength increases. Also, if the spatial distribution of the lateral slices of the bunch is biased, the electric field strength increases in the region where the charge and the electro-optic element 30 are close. Thereby, the birefringence effect in the electro-optic element 30 is increased, and the change in the polarization state is increased. When the change in the polarization state is large, the P-polarized component of the pulsed light is further reduced and the S-polarized component is further increased. Therefore, the shape of each recess is reflected in the charge distribution in the XY plane. That is, when the charge distribution in the XY plane becomes asymmetric, there is a difference in the shape of the eight recesses. The spectral distribution in each wavelength range changes according to the bunch shape on the XY plane. By comparing the P-polarized light components in the respective regions, it is possible to measure the electron distribution in the XY plane. Thereby, the bunch shape in the XY plane and the position of the bunch can be measured.

  Furthermore, when the time during which the electric field is applied to the electro-optic element 30 is increased, the width of the recess is increased. Therefore, the wavelength width of the dent corresponds to the bunch length of that region. Furthermore, the shape of each recess corresponds to a bunch shape in the Z direction. That is, the shape of the dent changes according to the bunch shape in the Z direction. Specifically, when the number of electrons contained in the bunch increases, the dent increases. Cut out and add the P-polarized light components in each wavelength range. By doing so, the bunch shape in the Z direction can be measured. Therefore, the three-dimensional spatial distribution of the electron beam 31 can be easily measured.

  Thus, by measuring the spectrum of the pulsed laser light that has passed through the polarizer 46, the electric field applied to the electro-optic element 30 is measured. That is, the distribution of the electric field generated by the electrons in the bunch 37 is measured. Thereby, the three-dimensional charge distribution of the bunch 37 can be estimated. That is, the intensity of the P-polarized light component in each region changes according to the spatial distribution of electrons in the bunch 37. Furthermore, it becomes possible to measure the profile in the Z direction. Therefore, the bunch length and the bunch width can be obtained. The three-dimensional shape of the bunch can be measured with a single shot.

  The dent generated in the P-polarized component in each region is developed in different wavelength ranges. In other words, the P-polarized component dents in the entire region have different wavelengths. Therefore, by measuring the spectrum using the spectrometer 50, the depressions of the P-polarized components in the regions A to H can be measured separately. Thereby, the spatial distribution in the XY plane can be measured. For example, a region where the number of electrons is large or a region where the number of electrons is small is determined. For this reason, the bias of the charge distribution in the bunch on the XY plane is measured. Furthermore, the spread of the bunch in the XY plane is measured. Further, since the chirped pulse laser beam is used, the wavelength corresponds to time. Therefore, the time distribution of the pulse laser beam can be measured. That is, the spectrum distribution corresponds to the time distribution. Thereby, the spatial distribution of the bunch 37 in the Z direction, that is, the bunch length can be measured. Specifically, the bunch shape can be measured by adding eight dents.

  In addition, by using the high-speed spectrometer 50, it is possible to cope with high repetition measurement up to MHz. Therefore, it is possible to measure the change of the bunch shape over time. In the above description, the P-polarized component is detected, but the S-polarized component may be detected. In other words, the S-polarized component may be taken out by the polarizer 46 and the spectrum may be measured. Further, both the P-polarized component and the S-polarized component may be measured. In this case, the S-polarized component and the P-polarized component of the pulse laser beam are branched by a polarizing beam splitter or the like. Then, spectrum measurement is performed for each polarization component. In this case, measurement is performed with two spectrometers.

  Note that the spectrum data measured by the spectrometer 50 is input to the processing device 55. That is, the processing device 55 is a computer having a storage area such as a CPU and a memory. For example, the processing device 55 includes a CPU (Central Processing Unit) that is an arithmetic processing unit, a ROM (Read Only Memory) and a RAM (Random Access Memory) that are storage areas, a communication interface, and the like. Perform the processing necessary to do it. For example, the ROM stores an arithmetic processing program for performing arithmetic processing, various setting data, and the like. Then, the CPU reads out the arithmetic processing program stored in the ROM and develops it in the RAM. Then, the program is executed in accordance with the setting data and the output from each sensor. The processing device 55 stores data in a storage device such as a memory or an external storage. Further, the processing device 55 has a monitor or the like for displaying the detection result. The spectrum of the pulse laser beam is displayed on the display screen. Further, the bunch shape calculated based on the spectrum is displayed. The spectral distribution changes according to the charge distribution of the bunch. Therefore, the charge distribution can be monitored by measuring the spectrum with the spectrometer 50.

  The electro-optic element 30 is preferably an organic polymer having a high-speed nonlinear response. Thereby, the time resolution can be set to 30 fsec, for example. As the organic polymer, for example, a polydiacetylene derivative can be used. Thus, the time resolution can be improved by using the electro-optic element 30 having a high response speed. If the time resolution is sufficiently shorter than the bunch length, the bunch can be sliced and measured. That is, the charge distribution when the bunch is sliced parallel to the XY plane can be measured. Specifically, a change in the shape of each recess corresponds to a temporal change in the electric field. Therefore, the temporal change of the charge distribution can be analyzed from the temporal change of the electric field. That is, it becomes possible to measure the shape when the bunch is sliced along the XY cross section. A processing example of the charge distribution measurement will be described with reference to FIGS.

  First, a case where a certain slice has only a monopole (monopole) moment component will be described with reference to FIG. In this case, the point charge can be regarded as passing through the center of the electro-optic element 30. In addition, FIG. 10 is a figure for demonstrating the case where there is only a monopole moment component. The left side of FIG. 10 schematically shows a perspective view of the electric field generated in the electro-optic element 30, and the right side shows a spectrum measured at that time. In addition, the electric charge has advanced in the direction of the dotted arrow.

  At the monopole moment, the electric field is point-symmetric. Electrons are accelerated to a relativistic region. In this case, the electric field is not coupled between adjacent slices. The electric field lines of the electric field in the XY plane are radial as indicated by the thick solid arrows. Accordingly, an electric field is applied to all the divided regions 30 a to 30 h of the electro-optic element 30 in parallel with the respective crystal axes. And the electric field strength of each division area 30a-30h becomes equal. In this case, the amount of change in the polarization state is equal in all regions A to H. That is, the P-polarized component of the pulsed laser light incident on the spectrometer 50 is equal in each region. Therefore, a spectrum as shown in FIG. 10 is measured. That is, the shapes of the eight dents (S polarization component) are equal. Note that the electrostatic potential of the monopole is inversely proportional to the distance.

  Next, a case where a slice has only a dipole moment component will be described with reference to FIG. That is, it can be understood that the electric dipole passes through the center of the electro-optic element 30. In addition, FIG. 11 is a figure for demonstrating the case where there is only a dipole moment component. The left side of FIG. 11 schematically shows a perspective view of the electric field generated in the electro-optic element 30, and the right side shows a spectrum measured at that time. The electric dipole advances in the direction of the dotted arrow.

  In a dipole, the positive and negative charges are separated by a small distance. The equipotential lines shown by dotted lines in FIG. 11 surround each charge of the dipole. The electric field lines connect two charges of the dipole. However, the electric field lines diverge in two directions (dipole direction). In the divided areas corresponding to these two directions, the electric field strength is high. In other words, the electric field strength is higher in the divided area crossed by the thick solid line arrow in FIG. 11 than in the other divided areas. In two divided regions facing each other, the polarization state changes greatly, and the P-polarized component becomes small. In this case, the recess (S-polarized component) becomes large in two of the eight divided regions. Here, the dent corresponding to the regions C and G is large. As described above, the two recesses (S-polarized components) corresponding to the regions C and G are deeper than the six recesses (S-polarized components) corresponding to the regions A, B, D, E, F, and H. Note that the electrostatic potential of the dipole is inversely proportional to the square of the distance.

  Further, a case where a certain slice has only a quadrupole moment component will be described with reference to FIG. That is, it can be understood that the electric quadrupole passes through the center of the electro-optic element 30. In addition, FIG. 12 is a figure for demonstrating the case where there is only a quadrupole moment component. The perspective view of the electric field generated in the electro-optic element 30 is schematically shown on the left side of FIG. 12, and the spectrum measured at that time is shown on the right side. The electric quadrupole advances in the direction of the dotted arrow.

  In a quadrupole, dipoles with the same moment are arranged in the opposite direction. The equipotential lines shown by dotted lines in FIG. 12 surround each charge of the quadrupole. In addition, the electric lines of force connect the positive and negative charges of the quadrupole. Therefore, the electric field of the quadrupole moment diverges in four directions, up, down, left, and right. In the divided areas corresponding to these four directions, the electric field strength is high. In other words, the electric field strength is higher in the divided area crossed by the thick solid line arrow in FIG. 12 than in the other divided areas. Every other four divided regions where the electric field strength is increased are arranged. At four electric field strengths, the polarization state changes greatly, and the P-polarized component becomes smaller. In this case, the dent (S polarization component) becomes large in four of the eight divided regions. Here, the depressions (S-polarized components) corresponding to the regions B, D, F, and H are large. As described above, the four recesses (S polarization component) corresponding to the regions B, D, F, and H are deeper than the four recesses (S polarization component) corresponding to the regions A, C, E, and G.

  Here, the electrostatic potential due to the charge in the bunch is approximated by the electric field of each moment. Then, the spatial distribution of monopoles, dipoles and quadrupoles is obtained from the electric field of each moment. Thereby, the charge distribution is obtained. That is, the bunch shape is measured by performing spectral decoding. Here, the electrostatic potential of the monopole is inversely proportional to the distance, the electrostatic potential of the dipole is inversely proportional to the square of the distance, and the electrostatic potential of the quadrupole is inversely proportional to the cube of the distance. Therefore, the electric field far from the center of gravity of the bunch charge can be approximated by a monopole. That is, when the distance is long, the electrostatic potential of the dipole and the quadrupole cannot be seen. However, when approaching, the electrostatic potential of a dipole can be seen, and when approaching further, the electrostatic potential of a quadrupole can be seen. Therefore, the charge distribution for each slice can be analyzed from the electric field applied to the electro-optic element 30 by the electrons in the bunch. The spectral distribution changes according to the charge distribution in the slice cross section. Therefore, the charge distribution for each slice can be analyzed by analyzing the spectral distribution.

  Of course, the approximation may be performed using not a quadrupole moment but a hexapole moment, an octupole moment, or a moment greater than that. However, since the hexapole is inversely proportional to the fourth power of the distance and the octupole is fifth to the fifth power of the distance, if the distance is sufficiently long, it can be ignored compared to the moment up to the quadrupole. Therefore, by approximating up to the quadrupole, the electrostatic potential in the XY plane can be approximated easily and accurately. Therefore, an accurate spatial distribution can be easily obtained. For such an approximation method, for example, SUWADA “Multiple Analysis of Electromagnetic Field Generated By Single-Bunch Electron Beams” can be referred to.

For example, assume that a spectrum as shown in FIG. 13 is measured. FIG. 13 is a diagram for explaining a state in which the bunch 37 is sliced and measured. In FIG. 13, the spectrum corresponding to the region F is shown enlarged on the entire spectrum. The spectrum corresponding to the region F indicates the electric field applied to the divided region 30f. Further, the change in the P-polarized light component in the wavelength range λ _{fL to} λ _fS indicates the bunch shape in the Z direction in the region F. The time change of the electric field applied to the divided region 30f corresponds to the shape of the dent corresponding to the region F. That is, different wavelengths in the wavelength range λ _{fL to} λ _fs indicate electric fields applied to the divided regions 30f at different times.

Therefore, the P-polarized component intensity at an arbitrary wavelength in each recess indicates an electric field at a certain timing in the bunch. Therefore, the charge distribution in each slice is calculated from the P-polarized component intensity at a specific wavelength in the recess. That is, by analyzing the P-polarized component intensity in the eight depressions for each wavelength, the charge distribution in the slice cross section can be obtained. For example, the wavelength of the region A in the slice sections _{W 1} in FIG. 13, lambda _a1. Similarly, the wavelengths of the regions B to H in the slice cross section W ₁ are respectively λ _a1 , λ _b1 , λ _c1, λ _d1, λ _e1, λ _f1 , λ _g1 , and λ _h1 (hereinafter referred to as λ _{b1 to} λ _h1 ). ). λ _a1 , λ _b1 , λ _c1, λ _d1, λ _e1, λ _f1 , λ _g1 , and λ _h1 are each shifted by a wavelength corresponding to Δt. By combining and analyzing the P-polarized light components in λ _{a1 to} λ _h1 , the electric field in the slice cross section W ₁ is obtained. That is, the P-polarized components of λ _{b1 to} λ _h1 are combined according to the position of the region. Thereby, the spatial distribution of the electric field strength is estimated. Then, the spatial distribution of the electric field strength is approximated by the electrostatic potential of each moment. Then, a charge distribution is obtained from the electrostatic potential. Thereby, a bunch shape can be calculated | required.

In slice sections _{W 1,} the electric field intensity of the electric field is applied to the divided areas 30a~30h is obtained. Based on the electric field strength, the charge distribution can be obtained. That is, the charge distribution is approximated by each moment component using the P-polarized components at these eight wavelengths. Then, when λ _a1 , λ _b1 , λ _c1, λ _d1, λ _e1, λ _f1 , λ _g1 , and λ _h1 are shifted to the short wavelength side, the charge distribution in the next slice section W ₂ can be obtained. . In this manner, eight wavelengths corresponding to the eight wavelength ranges corresponding to the regions A to F are extracted. Based on the extracted P-polarized light components at 8 wavelengths, the charge distribution in the XY plane can be measured. In addition, since the electrons are accelerated to the relativistic region, the electric field is not coupled between adjacent slices. Therefore, the charge distribution can be easily measured for each slice. Thus, by performing spectrum decoding, information regarding the charge distribution for each slice can be easily obtained.

  The time resolution by the above measuring method is limited according to the Fourier pulse limit and the pulse width of the chirped pulse laser beam. Specifically, it is proportional to the square root of the product of the pulse width of the Fourier pulse limit and the pulse width of the chirped pulse laser beam. Therefore, it is preferable to narrow the pulse width of the pulsed laser light incident on the electro-optic element 30. In this case, it is preferable to set the pulse width to about 10 times the bunch length in consideration of the jitter of the pulse laser beam and the bunch.

As mentioned above, the time resolution is limited by the Fourier pulse limit. Here, the time resolution can be further improved by calculating the actual electric field from the measured electric field. This calibration process will be described below. Here, if the actual actual electric field applied to the electro-optical element 30 is E _coul (τ), the measurement electric field measured based on the light that has passed through the electro-optical element 30 is E _coul (τ + t ₀ ) × cos (τ ² / α−π / 4). For this, see, for example, Jamison et al. Opt. Lett. 18 1710 (2003). Here, τ is time, t ₀ is the Fourier pulse limit, and α is the dispersion of the electro-optic element 30. Therefore, the actual electric field can be calculated backward from the measurement electric field. Thereby, time resolution can be improved. Note that the above reverse calculation may be compensated by the pulse waveform of the pulse laser beam incident on the electro-optic element 30. That is, by changing the pulse waveform from a rectangle, the actual electric field can be obtained directly from the spectrum distribution. Specifically, the intensity of each wavelength is changed based on the dispersion of the electro-optic crystal by controlling the modulation signal of the optical modulator 13a. Thereby, the electric field directly converted from the spectrum measurement becomes the actual electric field. Therefore, the spatial distribution of the electron beam can be easily measured.

  In FIG. 1, the polarization conversion element 42 is provided in the emission optical system 40, but the configuration is not limited thereto. For example, the polarization conversion element 42 can be omitted by using, as the polarizer 46, a polarizing plate in which the inclination of the absorption axis changes according to the position. For example, a polarizing plate having absorption axes arranged radially is used. Specifically, eight fan-shaped polarizing plates are prepared corresponding to the eight divided regions. And eight polarizing plates are arrange | positioned so that an absorption axis may become radial. That is, the absorption axis in each divided region is arranged so as to be parallel to the crystal axis of the electro-optic element 30 in FIG. In this case, the polarizer 46 takes out the azimuth polarization component and absorbs the radial polarization component. In other words, the spectrum corresponding to the S polarization component in FIG. 8 can be measured. Thereby, it is possible to extract a predetermined polarization component from each region without using the polarization conversion element 42. That is, as the electric field intensity generated by the electrons in the bunch increases, the component perpendicular to the absorption axis increases. Thereby, the spectral distribution measured by the spectrometer 50 changes according to the electric field intensity generated by the electrons in the bunch. For example, the spectrum corresponding to the S polarization component shown in FIG. 8 can be measured.

  For example, by combining eight different polarizing plates, a polarizer 46 having different absorption axes according to the incident position can be created. A polarizing plate having a different absorption axis direction is arranged for each of the radially divided divided regions. Thereby, it is possible to extract a predetermined polarization component without using the polarization conversion element 42. Therefore, the number of parts can be reduced, and the apparatus configuration can be simplified. Of course, it is possible to use a polarizer in which the absorption axes of the eight polarizing plates are not arranged radially, but the absorption axes of the eight polarizing plates are arranged circumferentially. In this case, an absorption axis is arranged in a direction perpendicular to the crystal axis of the electro-optic element 30 shown in FIG. Thereby, the spectrum corresponding to the P-polarized component shown in FIG. 8 can be measured.

  Further, by using the polarizer 46 as a polarization beam splitter, both the S-polarized component and the P-polarized component can be extracted. In this case, one can be used for the spectrum measurement and the other can be used for other applications. One branched light branched by the polarizer 46 is measured by the spectrometer 50, and the other branched light is used for temporal decoding described later. The P-polarized component can be used for the spectral decoding and the S-polarized component can be used for the temporal decoding. The temporal distribution (vertical spatial distribution) of the bunch can be measured by performing temporal decoding. Hereinafter, temporal decoding will be described with reference to FIG. FIG. 14 is a diagram illustrating a configuration for performing a bunch time distribution. In FIG. 14, the optical system shown in FIG. 1 is omitted as appropriate.

  The S-polarized component extracted by the polarizer 46 is incident on the nonlinear optical element 62. The nonlinear optical element 62 is, for example, a BBO crystal and generates a sum frequency. Here, the pulsed laser light of the S-polarized component extracted by the polarizer 46 is defined as measurement light 68.

  Further, at least a part of the pulsed laser light from the laser oscillator 11 is taken out. That is, a part of the pulsed laser light from the laser oscillator 11 is used for spectral decoding, and the rest is used for temporal decoding. The pulse laser beam from the laser oscillator 11 enters the variable delay 61. The pulse laser beam from the laser oscillator 11 enters the variable delay 61 without entering the broadband member 12. The variable delay 61 delays the incident pulse laser beam. The delayed pulsed laser light is incident on the nonlinear optical element 63. Here, the pulsed laser light emitted from the variable delay 61 is referred to as reference light 67.

  The reference light 67 enters the nonlinear optical element 62 in synchronization with the measurement light 68. That is, the delay time of the variable delay 61 is adjusted to synchronize the measurement light 68 and the reference light 67. Thereby, the measurement light 68 and the reference light 67 are incident on the nonlinear optical element 62 at the same timing. Note that the measurement light 68 and the reference light 67 are obliquely incident on the same surface (incident surface) of the nonlinear optical element 62. That is, the incident angle of the measurement light 68 and the incident angle of the reference light 67 are different. Then, the measurement light 68 and the reference light 67 intersect within the nonlinear optical element 62. In the nonlinear optical element 62, a sum frequency is generated due to the nonlinear optical effect. That is, a sum frequency is generated at the intersection position. Note that the pulse width of the reference light 67 is shorter than the pulse width of the measurement light 68.

  Here, how the measurement light 68 and the reference light 67 propagate in the nonlinear optical element 62 will be described with reference to FIG. FIG. 15 is a top view schematically showing the measurement light 68 and the reference light 67 propagating through the nonlinear optical element 62. In FIG. 15, measurement light 68 and reference light 67 passing through the nonlinear optical element 62 are shown in order from the top. Here, the states at the four timings are shown in order from the top. In FIG. 15, the earliest timing (for example, timing immediately after entering the nonlinear optical element 62) is shown in the first stage from the top, and the latest timing (for example, timing immediately before exiting from the nonlinear optical element 62) is upper. It is shown in the 4th row from. The measurement light 68 propagates in the upper left direction at each timing. The reference light 67 propagates in the upper left direction at each timing.

  When the measurement light 68 and the reference light 67 intersect, a sum frequency is generated by the nonlinear optical effect. The measurement light 68 and the reference light 67 cross each other at an angle. The intensity of the sum frequency light varies depending on the intensity of the measurement light 68 and the intensity of the reference light 67. Therefore, the position where the sum frequency is generated gradually changes. In FIG. 15, the position where the sum frequency is generated shifts from the right side to the left side as time elapses. The light generated by the sum frequency is detected by the array photodetector 63. In the array photodetector 63, light receiving pixels are arranged in an array. The sum frequency light that has passed through the nonlinear optical element 62 is detected by the array photodetector 63. Thereby, the time distribution of the pulse of the measurement light 68 can be measured. That is, the position on the light receiving surface of the array photodetector 63 corresponds to the position of the pulse in the time direction. Therefore, information in the time direction of the pulse is developed at a position on the light receiving surface of the array photodetector 63. The time distribution of the measurement light 68 is reflected in the measurement result of the array photodetector 63. As described above, the S-polarized light component reflects the bunch shape. By detecting the sum frequency by the array photodetector 63, the time distribution of the bunch can be measured.

  As described above, the delay element 43 shortens the pulse width of the pulse laser beam that has passed through the electro-optic element 30. Then, in the non-linear optical element 62, it intersects with the reference light 67 from the laser oscillator 11. Thereby, the time distribution of the bunch can be measured. Further, the bunch time distribution measured by temporal decoding can be used for the calibration. That is, the time distribution measured by the spectral decoding is calibrated by the time distribution measured by the temporal decoding. In the nonlinear optical element 62, the light generated by the nonlinear optical effect is separated from the reference light 67 and the measurement light 68 and measured by the array photodetector 63. The nonlinear optical effect in the nonlinear optical element 62 is not limited to the sum frequency generation. For example, difference frequency generation may be used.

  Further, the S-polarized component extracted by the polarizer 46 may be used for other purposes. For example, it can be used as a signal light for synchronizing pulsed light in an accelerator-based light source (radiation light source) and a laser pump probe. In the pump probe, for example, laser light is used as pump light, and pulsed radiation light is used as probe light. In such a pump probe, timing jitter of about picosecond is usually present due to electronics problems. Therefore, it is difficult to synchronize femtosecond or attosecond short pulse lasers with pulsed radiation. Therefore, it is used as signal light for synchronizing the S polarization component. Thereby, since the pulse light can be accurately synchronized, the problem of timing jitter can be improved.

  For example, NOPA (non-parallel optical parametric amplifier or non-coaxial optical parametric amplifier) amplification is performed using the S-polarized component as signal light and the second harmonic wave of Yb fiber laser as pump light (excitation light). . In the pump-probe photometry method, pulse light amplified by NOPA is used as pump light. Further, radiation light such as FEL generated from an electron beam is used as probe light. Of course, NOPA-amplified pulse light may be used as probe light, and light emitted from a quantum beam (such as synchrotron radiation light or FEL) may be used as pump light. Then, the probe light and the pump light are incident on the sample in synchronization. At this time, the pump light and the probe light are incident on the BBO crystal at an angle of several degrees. Since it can be optically delayed, it can be configured with all optics. For this reason, there is almost no jitter between the pump light and the probe light. The sample can be irradiated with the pump light and the probe light in precise synchronization. In this way, high-intensity femtosecond laser light synchronized with femtosecond electron bunches and femtoseconds can be used. A pump-probe measurement method using an ultrashort pulse becomes possible.

  In the above measurement apparatus, the laser pulse of the S-polarized component can be distributed as an optical trigger signal to the experimental user as it is using an optical fiber or the like. As a result, a measurement experiment using a measuring instrument (such as an optical switch) that moves with an optical trigger signal becomes possible. That is, a measurement experiment with femtosecond timing jitter becomes possible. Of course, if the intensity or wavelength of the S-polarized component is inappropriate as an optical trigger signal, enhancement, wavelength conversion, or wavelength selection can be performed by NOPA so as to suit the device. Thus, the S-polarized component can be used as an optical trigger signal for the measuring instrument.

  Furthermore, in the above description, the delay element 43 is provided in the emission optical system 40, but the delay element 43 may not be provided. That is, when one frame of the detection unit 52 of the spectrometer 50 is sufficiently long, it is not necessary to compress the pulse width using the delay element 43. Note that the pulse width can be reduced by using the delay element 43. In this case, it is necessary to increase the shooting speed of the detection unit 52. For example, by using the above-mentioned Phantom V10.0, it is possible to measure every bunch even with a repetition frequency of 153800 frames / sec (equivalent to 0.15 MHz). In this case, it is possible to perform measurement for several tens of minutes by directly storing the image data in the external storage. The total delay time of the delay element 43 and the delay element 23 may not be completely matched for each region. That is, the total delay time may be different in some areas.

  The direction of the crystal axis of the electro-optic element 30 is not limited to the radial direction. In addition, it becomes easy to receive the influence of the electric field by an electron by making the crystal axis of an electro-optical element radial. That is, since the phase change due to birefringence increases, the change in the polarization state by the electro-optic element 30 increases. Therefore, more accurate measurement can be performed. In this case, it is preferable to use a polarization conversion element 24 that converts linearly polarized light into radial polarized light. That is, it is preferable to make the vibration direction of the electric vector by the polarization conversion element 24 and the direction of the crystal axis parallel. Thereby, the amount of light received by the spectrometer 50 can be increased. Therefore, it can measure correctly. Of course, the vibration direction of the electric vector and the direction of the crystal axis need not be completely parallel.

  The arrangement of the polarization conversion element 24 and the delay element 23 may be reversed. In this case, the pulse laser beam emitted from the polarization conversion element 24 enters the delay element 23. Therefore, the pulsed laser beam in the radial polarization state is delayed in steps. Therefore, a time delay is given stepwise for each of the regions A to H. The arrangement of the polarization conversion element 42 and the delay element 43 may be reversed. In this case, the pulse laser beam emitted from the delay element 43 enters the polarization conversion element 42.

  In the above description, the measurement of the electron beam has been described. However, the measurement target is not limited to electrons. For example, a charged particle beam such as protons or ions can be measured. That is, a charged particle beam such as a charged particle accelerator can be measured. In addition, by accelerating to the relativistic region, the electric field is not coupled in the vertical direction. Therefore, it is suitable for measurement of charged particles accelerated to a relativistic region. Therefore, it is suitable for beam diagnosis of an accelerator. The charged particles are not limited to charged particles accelerated by an RF electric field, but may be charged particles accelerated by a DC electric field. That is, not only the RF accelerator but also the three-dimensional distribution of the electrostatic accelerator beam can be measured. In this case, the change with time of the shape of the charged particle beam can be measured. It is possible to measure the distribution of the beam in time and space.

  It is also possible to measure the energy distribution of electrons. For example, after bending the electron beam with a bending magnet or the like, the electro-optic element 30 is passed. When bent by a bending magnet, electrons are spatially dispersed according to the energy of the electrons. That is, the radius of curvature at the bending magnet varies depending on the energy of the electrons. For example, when a magnetic field in the Y direction is generated by a bending magnet, the electron beam is bent in the X direction. At this time, the position in the X direction corresponds to the energy of electrons. In this way, electrons are spatially dispersed according to energy. And it measures with respect to the electron beam bent by the bending magnet. By measuring the three-dimensional shape of the electron beam, the energy distribution in each slice in the bunch can be measured.

  Furthermore, not only a charged particle beam but also a three-dimensional spatial distribution of a light beam such as a laser beam or FEL can be measured. In the case of a light beam, the electric field generated by the light beam is measured. As a result, the polarization state of the light beam can be measured. That is, a three-dimensional measurement of the quantum beam can be performed. Here, the quantum beam includes not only a charged particle beam but also a light beam such as a laser beam. That is, any quantum beam that generates an electric field can be measured. When measuring a laser beam, for example, a pulsed laser beam to be measured is made incident on the electro-optic element 30. In this case, not the hollow electro-optic element 30 as shown in FIG. 6, but the electro-optic element 30 in which the electro-optic crystal is arranged at the center is used. Accordingly, the laser beam is incident on the electro-optic crystal in the vicinity of the optical axis. Birefringence occurs in the electro-optic crystal due to the electric field generated by the pulsed laser light. Therefore, the laser beam can be measured in the same manner as the charged particle beam. Thus, the pulse (bunch) shape of the quantum beam can be measured three-dimensionally. That is, the time distribution and the lateral space distribution can be measured with a simple configuration.

  For example, NOPA amplification is performed using the S-polarized component as signal light and the second harmonic wave of the Yb fiber laser as pump light (excitation light). The NOPA-amplified pulse light is used as pump light (or probe light) in the pump / probe photometry method. Further, a quantum beam which is a laser beam is used as probe light (or pump light) of the pump / probe photometry method. Then, the probe light and the pump light are incident on the sample in synchronization. There is almost no jitter between the pump light and the probe light. The sample can be irradiated with pump light and probe light in a state of being accurately synchronized. Thus, it is preferable to use one of the branched lights branched by the polarizer 46 in the pump / probe method. The other branched light branched by the polarizer 46 is amplified by NOPA. The sample is irradiated with the pulsed light amplified by NOPA as pump light (or probe light) in the pump / probe method. Further, the sample is irradiated with a quantum beam or light emitted from the quantum beam as probe light (or pump light). Thereby, the problem of timing jitter can be improved. Further, since a quantum beam subjected to three-dimensional measurement can be used, a pump / probe measurement method can be effectively performed.

  The polarization conversion element 24 may be disposed between the light source unit 10 of the axicon lens 21. In this case, since the polarization conversion element 24 can be made small, the component cost of the polarization conversion element 24 can be reduced. Further, even if the polarization conversion element 42 is disposed between the axicon lens 45 and the polarizer 46, the same effect can be obtained.

  Further, a relay optical system may be disposed between the polarization conversion element 24 and the electro-optical element 30. Thereby, the influence by the change of distribution of a polarization state can be reduced. That is, when the pulse laser beam propagates, the distribution of the polarization state in the beam cross section changes due to the diffraction effect. In this case, a change in the distribution due to diffraction may affect the electric field distribution at the focal plane. Therefore, by providing a relay lens, the polarization state immediately after passing through the polarization conversion element 24 and the polarization state immediately before entering the electro-optic element 30 are made substantially the same. Thereby, the influence by the change of the polarization state distribution by diffraction can be reduced.

It is a figure which shows typically the structure of the beam measuring apparatus concerning Embodiment 1 of this invention. It is a figure for demonstrating the pulse laser beam in the light source part of a beam measuring device. It is a figure for demonstrating the pulse laser beam in the light source part of a beam measuring device. It is a figure for demonstrating the delay element used for a beam measuring apparatus. It is a figure for demonstrating the polarization conversion element used for a beam measuring apparatus. It is a figure for demonstrating the electro-optical element used for a beam measuring apparatus. In a beam measuring device, it is a sectional view showing typically a pulse laser beam and a bunch which pass an electro-optic element. It is a figure for demonstrating the polarization state of the pulsed laser beam which passed the electro-optic element in the beam measuring device. It is a figure which shows the spectrum of the pulsed laser beam measured in the beam measuring apparatus. It is a figure for demonstrating an electric field when the bunch considered as a monopole passes the electro-optic element. It is a figure for demonstrating the electric field when the bunch considered as a dipole passes the electro-optic element. It is a figure for demonstrating an electric field when the bunch considered as a quadrupole passes the electro-optic element. It is a figure for demonstrating a mode when slicing and measuring an actual bunch. It is a figure which shows the structure for measuring a time distribution by temporal decoding. It is a figure which shows typically the light which passes a nonlinear optical crystal in the structure for measuring a time distribution by temporal decoding.

Explanation of symbols

10 light source unit, 11 laser oscillator, 12 broadband component,
13 chirping pulse waveform shaper, 13a optical modulator,
13b pulse stretcher, 13c optical amplifier,
14 wavelength plate, 15 Glan-laser and Karlsite polarizer,
20 incident optical system, 21 axicon lens, 22 axicon lens,
23 delay element, 24 polarization conversion element, 25 mirror,
23a-23h divided areas, 24a-24h divided areas,
30 Electro-optic element, 30a-30h Division area, 33 Hollow part 35a Pulse light, 35h Pulse light, 37 Bunch,
40 exit optical system, 41 mirror, 42 polarization conversion element, 43 delay element,
44 axicon lenses, 45 axicon lenses,
50 Spectrometer, 51 Spectrometer, 52 Detector, 55 Processing Device 61 Variable Delay, 62 Nonlinear Optical Element, 63 Array Photodetector,
67 Reference light, 68 Measurement light

Claims (33)

A beam measuring device that three-dimensionally measures a quantum beam using a pulsed laser beam,
A light source unit that shapes and emits a pulse waveform of the pulsed laser light so that the wavelength of the pulsed laser light oscillated by the laser oscillator changes according to time;
A first delay element that gives a time delay corresponding to an incident position to the pulsed laser light emitted from the light source unit, and a first polarization conversion element that converts the pulsed laser light into different polarization states according to the incident position An incident optical system comprising:
An electro-optic element disposed in the beam path of the quantum beam and having a different crystal axis depending on the incident position;
A polarizer for extracting a predetermined polarization component from pulsed laser light incident from the incident optical system via the electro-optic element;
And a measuring instrument for measuring a spectrum of the pulsed laser light extracted by the polarizer.   The beam measuring apparatus according to claim 1, wherein the electro-optic element is provided with a plurality of radially arranged electro-optic crystals so that the crystal axes of the electro-optic element are radial. The first polarization conversion element has a plurality of radially divided regions;
In a plane perpendicular to the optical axis of the pulsed laser light, a plurality of electro-optic crystals provided in the electro-optic element are arranged at positions corresponding to divided regions provided in the first polarization conversion element,
The first polarization conversion element converts the polarization state so that an oscillation plane of an electric vector of pulsed laser light incident on the electro-optic element is in the same direction as the radial crystal axis. Beam measuring device.   The first delay element delays the pulsed laser light in a stepwise manner in accordance with an incident position so as to correspond to a plurality of divided regions provided in the first polarization conversion element. 4. The beam measuring apparatus according to 3.   The beam measuring apparatus according to claim 4, wherein a stepwise delay time given by the first delay element is longer than a pulse of the quantum beam. The plurality of divided regions provided in the first polarization conversion element are each provided with a wave plate that emits light with the phase of incident light shifted,
6. The beam measuring apparatus according to claim 3, 4, or 5, wherein the optical axes of the wave plates are substantially orthogonal in the opposed divided regions. The maximum delay time given by the first delay element is shorter than the pulse width of the pulse laser beam emitted from the light source unit;
7. The pulse laser beam that has been given a time delay by the first delay element has an overlap period in which the pulse laser beam overlaps in time over the entire optical axis of the pulse laser beam. Any one of the beam measuring devices. In synchronization with the timing when the pulse laser beam of the overlapping period passes through the electro-optic element,
The beam measuring apparatus according to claim 7, wherein the pulse of the quantum beam passes through the electro-optic element. A second delay element that gives a time delay according to an incident position to the pulsed laser light emitted from the electro-optic element, and shortens a pulse width of the light incident on the polarizer;
A non-linear optical element on which a part of the pulsed laser light oscillated by the laser oscillator is incident as reference light,
The polarizer branches the pulse laser beam according to the polarization direction,
Measure one branched light branched by the polarizer with the measuring device,
Making the other branched light branched by the polarizer incident on the nonlinear optical element, crossing the reference light in the nonlinear optical element,
9. The beam measuring apparatus according to claim 1, wherein light generated by a nonlinear optical effect in the nonlinear optical element is measured by an array detector.   The beam measuring apparatus according to claim 9, wherein the pulse widths of the pulse laser beams are substantially equal before entering the first delay element and after emitting the second delay element.   The beam measuring apparatus according to claim 1, wherein the electro-optic element is provided with a hollow portion through which the quantum beam passes. A pair of axicon lenses that make the pulsed laser light incident on the electro-optic element annulus;
The beam measuring apparatus according to claim 11, wherein the annular pulse laser beam passes outside the hollow portion. A second polarization conversion element on which the pulse laser beam emitted from the electro-optic element is incident;
The beam measuring apparatus according to claim 1, wherein the second polarization conversion element converts the polarization state to a different polarization state according to an incident position.   The beam measuring apparatus according to claim 13, wherein the first polarization conversion element and the second polarization conversion element have optical axes in the same direction.   The beam measuring apparatus according to claim 1, wherein the measuring device is a spectroscopic measuring device that performs spectrum measurement by splitting the pulsed laser light.   The beam measuring apparatus according to claim 15, wherein the spectrum of one pulse of the pulsed laser light is obtained in one frame of the array detector for a spectrometer that is provided in the spectrometer. A beam measurement method for three-dimensionally measuring a quantum beam using a pulsed laser beam,
Shaping and emitting the pulse waveform of the pulsed laser light so that the wavelength of the pulsed laser light oscillated by the laser oscillator changes with time; and
Providing the shaped pulsed laser light with a time delay according to an incident position, and converting the pulsed laser light into a different polarization state according to the incident position;
Making the pulse laser beam given the time delay incident on an electro-optic element arranged in the beam path of the quantum beam and having a different crystal axis depending on the incident position;
Extracting a predetermined polarization component from the pulse laser beam emitted from the electro-optic element;
Measuring a spectrum of a predetermined polarization component extracted from the pulsed laser beam.   The beam measuring method according to claim 17, wherein the electro-optic element is provided with a plurality of radially arranged electro-optic crystals so that the crystal axes of the electro-optic element are radial. In the step of converting the pulsed laser light into different polarization states depending on the incident position,
The pulsed laser light is incident on a first polarization conversion element having a plurality of radially divided regions,
In a plane perpendicular to the optical axis of the pulsed laser light, a plurality of electro-optic crystals provided in the electro-optic element are arranged at positions corresponding to divided regions provided in the first polarization conversion element,
19. The first polarization conversion element converts a polarization state so that a vibration plane of an electric vector of pulsed laser light incident on the electro-optic element is in the same direction as the radial crystal axis. Beam measurement method. A time delay corresponding to the incident position is given by the first delay element provided in the optical path of the pulse laser beam,
The beam measuring method according to claim 19, wherein the first delay element delays the pulsed laser light in a stepwise manner according to an incident position so as to correspond to a plurality of divided regions provided in the first polarization conversion element. .   21. The beam measuring method according to claim 20, wherein a stepwise delay time provided by the first delay element is longer than a pulse of the quantum beam. The plurality of divided regions provided in the first polarization conversion element are each provided with a wave plate that emits light with the phase of incident light shifted,
The beam measurement method according to claim 19, 20, or 21, wherein the optical axes of the wave plates are substantially orthogonal in the opposed divided regions. The maximum delay time given to the pulse laser beam is shorter than the pulse width of the pulse laser beam emitted from the light source unit,
The beam according to any one of claims 17 to 22, wherein the pulse laser beam to which the time delay is given has an overlapping period in which the pulse laser beam overlaps in time over the entire outer periphery of the optical axis of the pulse laser beam. Measuring method. In synchronization with the timing when the pulse laser light of the overlapping time passes through the electro-optic element,
The beam measurement method according to claim 23, wherein the pulse of the quantum beam passes through the electro-optic element. Providing a time delay according to the incident position for the pulsed laser light emitted from the electro-optic element, and shortening the pulse width;
A step of causing a part of the pulsed laser light oscillated by the laser oscillator to enter the nonlinear optical element as reference light, and
In the step of extracting a predetermined polarization component from the pulse laser beam, the pulse laser beam is branched according to the polarization direction using a polarizer,
In the step of measuring the spectrum, a spectrum of one branched light branched by the polarizer is measured,
The other branched light branched by the polarizer is incident on the nonlinear optical element, and the reference light is crossed in the nonlinear optical element,
The beam measurement method according to claim 17, wherein light generated by a nonlinear optical effect in the nonlinear optical element is measured by an array photodetector.   26. The beam measuring method according to claim 25, wherein the pulse width of the pulse laser beam is substantially equal before entering the electro-optic element and after the pulse width is shortened.   27. The beam measurement method according to claim 16, wherein the electro-optic element is provided with a hollow portion through which the quantum beam passes. A pair of axicon lenses that make the pulsed laser light incident on the electro-optic element annulus;
28. The beam measuring method according to claim 27, wherein the annular pulse laser beam passes outside the hollow portion.   29. The beam measurement method according to claim 17, further comprising a step of converting the pulse laser beam emitted from the electro-optic element into a different polarization state depending on an incident position.   A first polarization conversion element that converts the shaped pulsed laser light into a different polarization state according to an incident position, and a first polarization conversion element that converts the pulsed laser light emitted from the electro-optic element into a different polarization state according to the incident position. 30. The beam measuring method according to claim 29, wherein the two electro-optic elements have wave plates having optical axes in the same direction.   The beam measuring method according to any one of claims 17 to 30, wherein in the step of measuring the spectrum, the pulsed laser beam is spectrally measured using a spectrometer that performs spectrum measurement.   32. The beam measurement method according to claim 31, wherein the spectrum of one pulse of the pulsed laser light is acquired in one frame of the array detector for a spectrometer provided in the spectrometer. A pump / probe measurement method using a beam measured by the beam measurement method according to claim 17,
In the step of extracting a predetermined polarization component from the pulse laser beam, the pulse laser beam is branched according to the polarization direction using a polarizer,
In the step of measuring the spectrum, a spectrum of one branched light branched by the polarizer is measured,
The other branched light branched by the polarizer is subjected to NOPA amplification, and the sample is irradiated as one of pump light and probe light,
A pump / probe measurement method in which a sample is irradiated with the quantum beam or light emitted from the quantum beam as the other of pump light and probe light.

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