JP6233857B2 - Two-dimensional four-mirror resonator - Google Patents

Description

  The present invention relates to an optical resonator for performing laser Compton scattering.

  In recent years, research and development of small X-ray generators using laser Compton scattering have attracted attention. Laser Compton scattering is the generation of radiation such as X-rays by the collision of pulsed laser light and an electron beam. In order to perform laser Compton scattering, a laser beam having a very high laser intensity (pulse intensity) per pulse and a high-intensity electron beam are required. However, the production of a laser beam having a high pulse intensity has been very difficult as described below. On the other hand, a high-intensity electron beam could be produced by a circular accelerator such as a synchrotron or a cyclotron. Therefore, conventionally, it has been proposed that a laser oscillator be placed in the electron beam circuit of the circular accelerator to perform laser Comptonton scattering. However, since the circular accelerator is a huge device having a circumference of several kilometers, the above method is not suitable for industrial use.

  The circular accelerator can generate high-intensity coherent X-rays in the range of several keV to 100 keV. However, such a cyclotron will never be used for industrial use because of its enormous size. However, until now, there have been few known small devices that generate strong X-rays as well as synchrotron X-rays.

  Conventionally, an optical resonator is known as a means for generating laser light. The optical resonator is a laser amplifying means that amplifies the laser light generated by stimulated emission from the stimulated emission material by laser interference on the surface of the resonant mirror while reflecting it by the opposing mirror, and the laser depends on the reflectivity of the resonant mirror. Can be adjusted. In principle, a method using an optical resonator can amplify and store laser light with a compact optical resonator. As the optical resonator, a ring-shaped Fabry-Perot resonator, a Michelson interferometer resonator having a reflecting mirror, a Fox Smith interferometer resonator, and the like are known.

The principle of laser amplification by an optical resonator is that it is performed by satisfying a condition that the resonator length matches an integral multiple of a half wavelength of laser light. This is called standing waves. Since the resonance width of the standing wave is determined by the reflectivity of the resonant mirror, it becomes narrower as a higher reflectivity mirror is used to obtain a higher amplification factor. For example, assuming an optical resonator with a gain of 1000 times using a reflector having a reflectivity of 99.9%, the resonance width is 24 kHz and the resonance position is about 1 mm (10 ⁻¹⁰ m). The resonance state is easily lost due to environmental disturbances such as vibration. In order to maintain the laser resonance state, it is necessary to drive the resonance mirror with piezo drive and perform advanced feedback control, but conventional optical resonators maintain resonance stably due to the limitations of mechanical control. It is said that the technical limit that can be achieved is about 1000 times the amplification factor.

  Until now, many laser amplifiers using an optical resonator have been proposed (Patent Documents 1 to 5, Non-Patent Document 1). Patent Document 1 discloses a simple structure for optical transmission using a Fabry-Perot type resonator having a laser cavity filled with a rare earth-doped optical fiber for optical communication, a Fox Smith interferometer type resonator having a reflecting mirror, or the like. A laser oscillator is disclosed. The purpose of these laser oscillators is a laser oscillator for supplying a clean optical carrier of longitudinal mode selection, not a laser generator for generating a laser with high pulse intensity. In this type of laser oscillator, even if the oscillation output is increased due to a shift in the resonance width due to thermal vibration, the pulse intensity is limited to a microjoule level at most.

  Non-Patent Document 1 discloses generation of a single-frequency laser pulse using a Fox Smith interferometer type resonator having a concave mirror as a resonant mirror and a piezo adjuster for mechanically controlling the resonant mirror. doing. It has been reported that the output of the laser beam generated by this method is at most 15 mW due to the low amplification factor as described above.

  In Patent Document 2, an individual laser (stimulated emission medium) is provided in an optical resonator, and pumping light (excitation laser) generated by injecting a current into a laser diode is incident on the individual laser to generate laser light. Disclosed. This method is a convenient method of generating laser light because the laser diode is inexpensive and small, but the generation and accumulation of high-intensity laser light sufficient to cause laser Compton scattering is described above. This is difficult because of the low amplification factor.

  Patent Document 3 discloses a laser amplifier pumped by a diode. This amplifier is a device for focusing a laser beam on a medium by providing a thermal lens in a resonator having a laser active solid medium therein. However, even if this means is used, it is difficult to generate and accumulate high-intensity laser light sufficient to cause laser Compton scattering because of the low amplification factor as described above.

  Patent Document 4 discloses an apparatus that generates laser light using a high-intensity mode-locked laser oscillator and an optical resonator in order to generate X-rays by laser Compton scattering. However, the high-intensity mode-locked laser oscillator is a very expensive large-sized device, and very advanced feedback control technology is required to guide the laser from the oscillator to the optical resonator and amplify it stably. Since the amplification of about 1000 times is the limit, the pulse intensity of the laser beam that can be generated by this method is about 100 μJ.

  Patent Document 5 discloses that a multistage amplification laser system in which a plurality of optical resonators are arranged in series is used for semiconductor exposure. Although this optical resonator uses a reflecting mirror, it is an optical resonator that is difficult to accumulate in the laser, so it is a device that gradually increases the amplification of laser light by transmitting it to the optical resonator in the subsequent stage. is there. Since the amplification factor of laser light is limited by the control accuracy of the mechanical resonance width, if an attempt is made to increase the laser amplification factor sufficient for laser Compton scattering using this type of optical resonator, many optical resonators will be used. Therefore, a multistage amplification laser system in which a plurality of such optical resonators are arranged is actually laser Compton scattered. It is almost difficult to use as a laser light source.

  In principle, it is possible to generate high-intensity laser light by combining a high-power pump laser light source, a large optical resonator, and a high-power high-frequency oscillator, but the entire device becomes very large. Therefore, it is not suitable for industrial use.

  Further, in the optical resonator as described above, although the amplification factor is small, the laser beam can be amplified, but a polarized laser cannot be generated.

  Conventionally, several apparatuses for generating X-rays by inverse Compton scattering using an optical resonator have been proposed (Patent Documents 6-8).

  In Patent Document 6, a Fox Smith interferometer type resonator having a pair of mirrors is provided in an electron beam peripheral circuit of a circular accelerator, and an X-ray is generated by colliding a laser beam and an electron beam in the resonator. An apparatus for generating is disclosed. Since the laser light introduced into the optical resonator is laser light only from the laser oscillator, the amplification factor of the laser light is at most 1000 times as described above, no matter how high the reflectivity of the reflecting mirror is. Due to the limit, it is difficult to generate intense laser Compton scattered X-rays with the device.

  In Patent Document 7, an electron beam is introduced into an optical resonator in which concave mirror groups in which a plurality of concave mirrors are arranged in the same row in a single optical resonator structure, and collides with repetitively reflected laser light in the optical resonator. An apparatus for generating short-wavelength light is disclosed. The apparatus improves the collision frequency by colliding the laser beam and the electron beam in the convergence region of the laser beam repeatedly reflected between the individual concave mirrors, and the collision is performed between the plurality of concave mirrors. This is a device. However, since the laser light accumulated in the optical resonator is simply a mode-lock laser from the laser light source and is repeatedly reflected between a pair of opposing concave mirrors (resonator provided with a pair of opposing concave mirrors). Is structurally the same as the Fox Smith interferometer type resonator), and the amplification factor of the laser light is only about 1000 times as described above. Therefore, as described in the invention, the apparatus is an apparatus for generating short-wavelength light for photolithography, and it is difficult to generate intense laser Compton scattered X-rays by the apparatus. is there.

  In Patent Document 8, a Fox Smith interferometer type resonator having two ultrahigh reflection mirrors is placed in an electron beam circuit of a circular accelerator, the laser beam accumulated in the resonator, and the generation of the accelerator. An apparatus for generating an X-ray or γ-ray by colliding an electron beam in a resonator is disclosed. Also disclosed is an apparatus for generating X-rays or γ-rays by arranging the resonators in the same row in a circular circuit of an electron beam of a circular accelerator. However, since the resonator used in this apparatus is a normal optical resonator in which two concave mirrors are opposed to each other, an extremely high reflective mirror having a reflectivity of 99.99984% is used as a concave mirror. Even if it is used, the amplification factor of the laser beam is limited to about 1000 times as described above, so that it is difficult to generate strong laser Compton scattered X-rays with this apparatus.

  The development of an optical resonator capable of generating a laser beam having a pulse intensity of about 1 mJ or more has a problem of a laser durable resonator mirror. Conventionally, laser-resistant resonator mirror materials include optically synthesized quartz glass with high laser resistance for semiconductor exposure apparatuses (Patent Document 9), high-purity silica glass material with low refractive index having laser damage resistance ( Patent Document 10), synthetic quartz glass with high laser resistance (Patent Document 11), optical quartz glass for excimer laser with excellent laser resistance (Patent Document 12), laminated metal film for excimer laser with excellent laser resistance ( Patent Document 13), a dielectric multilayer film composed of a high refractive index tantalum oxide thin film and a low refractive index silica thin film (Patent Document 14), a ceramic material such as sapphire (Patent Document 15), and the like are known. In addition, it has been proposed to form a multilayer film structure including a diamond layer having high thermal conductivity as a multilayer film reflecting mirror in an optical device such as a surface emitting semiconductor laser (Patent Document 16).

  However, it has been found through experiments by the present inventors that many of the resonant mirrors and reflecting mirrors using the materials listed above are destroyed by repeated resonance of laser light having a pulse intensity of about 300 μJ.

  Under the circumstances as described above, the present inventors arranged a pair of plane mirrors and a pair of concave mirrors in a three-dimensional manner in order to generate a high-intensity polarized laser for enabling laser Compton scattering. A revolutionary three-dimensional four-mirror resonator was proposed (Patent Document 17). However, the above three-dimensional optical resonator requires a very advanced resonance matching technique between the resonant laser beam in the resonator and the incident laser beam to reduce the beam size of the laser beam due to the three-dimensional arrangement of the mirrors. It was.

  As described above, various laser generators using conventional optical resonators are known as laser generators for material processing and laser oscillators for optical communication, but generate laser Compton scattered X-rays. A small-sized optical resonator that generates a high-intensity polarized laser for the purpose has been hardly known.

P. W. Smith, Stabilized single-frequency output from a long laser cavity, IEEE Journal of Quantum Electronics, 1965, 11, Vol.QE-1, No. 8, pp. 343-348.

JP-A-6-318751 JP 2002-141589 A JP-A-5-75189 JP 2009-16488 A JP 2011-166169 A U.S. Pat. No. 4,598,415 Japanese Unexamined Patent Publication No. 7-110400 Japanese Patent Laid-Open No. 11-211899 JP 2010-150097 A JP 2010-155778 A JP 2009-190958 A JP 2000-191329 A Japanese Patent Laid-Open No. 10-160915 JP 2006-30288 A JP 2004-356479 A JP-A-10-233558 JP 2011-34006 A

  As described above, the conventional laser Compton scattering device was based on the idea of using a huge circular accelerator as an electron beam source, and was not used for industrial use. The present inventors changed the idea of performing laser Compton scattering in an optical resonator using an electron beam generated by a micro linear accelerator. Since the electron beam generated by the linear accelerator is not an orbiting electron beam, the optical resonator must also have a container for performing laser Compton scattering. The present invention is based on the idea of generating a high intensity laser for laser Compton scattering in an optical resonator.

  An object of the present invention is to provide an optical resonator capable of generating a high-intensity polarized laser beam in order to perform laser Compton scattering with an electron beam supplied to the resonator based on the above idea.

  The inventors of the present invention need only have a pulse intensity of about 100 μJ for generating a quasi-monochromatic X-ray of about several keV by laser Compton scattering, but medical diagnosis, treatment, material structure analysis, material analysis, etc. It is estimated that the pulse intensity of the laser beam necessary for generating a high-luminance quasi-monochromatic X-ray having high industrial applicability is about 1 millijoule. Further, in order to generate high-intensity quasi-monochromatic X-rays for diagnosis and treatment, in order to generate high-intensity quasi-monochromatic X-rays by laser Compton scattering, a high-intensity whose normalized emittance is 10 μm-rad or less. It is estimated that the electron beam is necessary.

  As a result of intensive studies to achieve the above object, the present inventors have achieved a very strong laser by using a two-dimensional four-mirror optical system in which a pair of cylindrical concave mirrors and a pair of concave mirrors are arranged on the same plane. It was found that light can be generated, and the present invention has been completed based on this finding.

The present inventors generate a very strong polarized laser having a pal intensity of 1 mJ or more and a beam size of 5 μm by a two-dimensional four-mirror optical system provided with a pair of cylindrical concave mirrors and a pair of concave mirrors arranged in a two-dimensional plane. I found that I could do it. The pulse intensity and beam size, as compared with the pulse intensity and beam size of a conventional laser beam, respectively, ¹⁰⁹ times higher, 100 times smaller. Based on this discovery, the present inventors provide a new compact optical resonator that can generate high-intensity quasi-monochromatic polarized X-rays that are as strong as conventional synchrotron radiation X-rays.

That is, the present invention
1.
A pair of cylindrical concave mirrors and a pair of concave mirrors arranged on a two-dimensional plane, a resonance length adjusting means for adjusting the length of the optical path, and a laser Compton scattering unit for colliding the laser beam with the electron beam are provided. A two-dimensional four-mirror optical system, a laser inlet for introducing laser light into the two-dimensional four-mirror optical system, an electron beam inlet for introducing an electron beam into the laser Compton scattering unit, and laser Compton scattered X-rays A two-dimensional four-mirror resonator provided with a radiation outlet to be extracted, wherein the laser beam introduced from the laser introduction port into the two-dimensional four-mirror optical system is introduced from the electron beam introduction port. Most of the laser Compton scatter part is collided in the beam and the laser Compton scatter part so that the laser Compton scattered X-ray can be taken out from the radiation outlet. It has a structure of the two-dimensional 4 KagamiHikari resonator, wherein is fit.
2.
A polarization control unit for controlling the polarization of the two-dimensional four-mirror optical system and a resonance control unit for controlling the resonance of the two-dimensional four-mirror optical system are further provided, and the laser is passed through the polarization control unit and the resonance control unit. 2. The configuration of the two-dimensional four-mirror resonator according to 1 above, wherein the beam is separated into a right circularly polarized laser beam and / or a left circularly polarized laser beam according to the length of the optical path and amplified. It was.
3.
A mode-locked laser oscillator that supplies a mode-locked laser, and a laser light source unit that includes a resonance matching unit that matches the resonance state of the two-dimensional four-mirror resonator and the resonance state of the mode-locked laser oscillator. The configuration of the two-dimensional four-mirror resonator according to the above item 2, wherein the supplied laser beam is stably amplified.

  The present invention described in 1 above can generate a laser beam having a pulse intensity of 1 mJ or more and a beam size of 30 μm or less.

  The present invention described in 2 above can selectively generate a right circularly polarized light and / or a left circularly polarized laser beam having a pulse intensity of 1 mJ or more and a beam size of 30 μm or less.

  In the third aspect of the present invention, the resonance state of the two-dimensional four-mirror resonator and the resonance state of the mode-locked laser can be automatically matched. Amplification can be performed stably, which can produce a surprisingly high intensity laser beam.

  Further, the present invention collides a polarized laser beam having a pulse intensity of 1 mJ or more and a beam size of 30 μm or less with an electron beam having a quality characteristic of a normalized emittance of 10 μm-rad or less in a collision angle range of 0 to 20 degrees. By doing so, high-intensity quasi-monochromatic X-rays that are as strong as synchrotron radiation X-rays can be generated.

  The present invention is a new compact optical resonator and a two-dimensional four-mirror optical resonator equipped with a two-dimensional four-mirror optical system capable of generating a high-intensity laser beam and high-intensity X-rays. The two-dimensional four-mirror optical system can generate a high-intensity laser beam having an ideal circular beam profile, and can selectively generate right and left circularly polarized laser beams. It is an optical system that enables resonance matching of incoming and outgoing laser beams and enables collision (laser Compton scattering) between the laser beam and the electron beam in the optical system. Thus, the present invention can selectively generate high-intensity polarized X-rays that are as strong as synchrotron radiation X-rays.

It is a figure explaining the optical parameter of the two-dimensional four mirror optical resonator used for this invention. It is the schematic explaining one of the optical resonators of this invention. It is a conceptual diagram explaining the block diagram of the two-dimensional four mirror optical resonator to which the laser light source unit provided with the resonance matching unit, the polarization control unit, and the resonance control unit are attached. FIG. 4 is a conceptual diagram illustrating a block diagram of a two-dimensional four mirror optical resonator in which an electron beam generating unit E is attached to the optical resonator of FIG. 3. It is a figure which shows the relationship between the laser size and S-parameter of the two-dimensional four-mirror resonator used for this invention. It is a figure which shows the relationship between the pulse intensity of the laser beam produced | generated by this invention, and the electric current value of an excitation laser light source. It is a figure which shows the resonance state of the laser beam produced | generated by this invention.

  The present invention is an optical resonator equipped with a two-dimensional four-mirror optical system capable of generating a high-intensity laser beam for colliding with an electron beam.

  The two-dimensional four-mirror resonator basically has a two-dimensional four-mirror optical system in which a pair of cylindrical concave mirrors and a pair of concave mirrors are two-dimensionally arranged, and the length of an optical path formed in the optical system. Resonator length adjusting means for adjusting, laser introducing port for introducing a laser beam, electron beam introducing port for introducing an electron beam, a laser Compton scattering unit for colliding a laser beam and an electron beam, and the laser Compton scattering And a radiation outlet for taking out the radiation generated in the section to the outside.

  The cylindrical concave mirror is a mirror whose inner curved surface is a semi-cylindrical curved surface, and the curved surface is a mirror surface. The concave mirror is a mirror having a curved inner curved surface as a mirror surface.

  In general, in a two-dimensional four-mirror optical system in which a pair of plane mirrors and a pair of concave mirrors are arranged on the same plane, the incident direction and the reflection direction of a laser beam are not perpendicular to each mirror. Due to this tilt, the vertical and horizontal focal lengths of the concave mirrors do not match, and the beam profile at the laser convergence point at the midpoint between the concave mirrors becomes elliptical. Since the elliptical laser beam has a larger beam cross-sectional area than the true circular laser beam, the luminance is low.

  The present invention has found for the first time that the beam profile can be narrowed down to a perfect circle by using a cylindrical concave mirror instead of the plane mirror. Thereby, the brightness | luminance of the laser beam produced | generated by the two-dimensional four mirror optical resonator used by this invention can improve a brightness by orders of magnitude rather than the laser beam by the conventional optical resonator.

  In addition, by using a cylindrical concave mirror, a parallel beam having a perfect circular beam profile can be obtained, so that laser incident matching becomes very easy and laser transmission matching is the same. The 4-mirror resonator can easily adjust the laser beam optics. Conventionally, the two-dimensional four-mirror optical system used in the present invention is hardly known.

  The reflectivity of the cylindrical concave mirror and the concave mirror is optimized so as to increase the resonance sharpness of the optical resonator. Finesse (F) has a relationship of the reflectance (R) and Formula 1.

  As R increases, F can be increased. Another reason for increasing the reflectivity is to prevent the surface of the concave mirror from being damaged by a high-intensity laser collision (increasing laser durability).

  One of the pair of cylindrical concave mirrors provided in the optical system and one of the pair of concave mirrors preferably have a reflectance of 99.9% or more, respectively, and the reflectance is 99. More preferably, it is 99% or more and less than 100%. When the reflectivity is 99.9% or less, the decrease in the fineness of the concave mirror is increased, and an adverse effect due to the collision of the laser beam on the concave mirror surface is liable to occur. If it is .99% or more, it is preferable not only because the fineness of the optical resonator can be made very large but also the adverse effect caused by the collision of laser light can be reduced. The reason why the reflectance is less than 100% is that the reflectance is less than 100% because laser light enters and exits. Usually, a concave mirror having a reflectivity of about 99.999% or more is used.

  As the cylindrical concave mirror and the concave mirror, a mirror whose surface is coated with a dielectric multilayer film is usually used. A mirror coated with a dielectric multilayer film has a relatively higher laser durability than a mirror used in a conventional optical resonator. Preferred examples of the mirror include, but are not limited to, a mirror coated with a fluorine-containing dielectric multilayer film and a mirror coated with a single crystal diamond thin film.

  The resonator length adjusting means for adjusting the length of the optical path formed in the optical resonator is means for controlling the optical path length between the concave mirrors. The means is provided in each holder that supports the concave mirror, and is a mechanism that can move with the holder with high accuracy in accordance with the applied voltage depending on the resonance state. As the resonator length adjusting means, piezoelectric control means having a piezoelectric element is preferable.

  The laser Compton scattering unit is a place where laser Compton scattering is performed by colliding a laser beam and an electron beam in a two-dimensional four-mirror resonator. The collision with the electron beam can be achieved by precisely controlling the incident angle close to the frontal collision with the electron beam traveling toward the laser beam by an electromagnet provided in front of the laser Compton scattering unit. The laser Compton scattering part is usually provided on the optical path of the two-dimensional four-mirror optical system, and is most preferably provided at the center of the resonance length where the beam size (also referred to as the beam waist) of the resonance laser light is minimized. preferable. By doing so, as will be described later, in performing laser Compton scattering, the laser beam of the optical system is strengthened most in the laser Compton scattering portion.

  The laser introduction port for introducing the laser beam is usually an optical resonator structure that houses the optical system so that the laser beam can be incident on a cylindrical concave mirror provided in the optical system at an appropriate incident angle. Is provided on the side.

  An electron beam introduction port for introducing the electron beam is usually provided on a side portion of the optical resonator structure housing the optical system so that the electron beam can be incident on the Compton scattering unit at an appropriate incident angle. .

  The radiation extraction port for extracting the radiation generated in the laser Compton scattering unit is usually located on the side of the optical resonator structure housing the optical system so that the radiation from the Compton scattering unit can be extracted at an appropriate extraction angle. Provided.

  In order to generate high-intensity X-rays at the laser Compton scattering part, the smaller the beam size and the higher the pulse intensity, the better. The laser beam collided in the laser Compton scattering part is preferably a polarized laser having a pulse intensity of 1 mJ or more and a beam size of 30 μm or less. Further, a polarized laser having a pulse intensity of 1 mJ or more and a beam size of 20 μm or less is more preferable. This is because if the beam size is 30 μm or less and the pulse intensity is 1 mJ or more, a microbeam of high-intensity radiation can be generated. Further, since the theoretical lower limit of the beam size by the two-dimensional four-mirror resonator used in the present invention is about 5 μm, the lower limit of the beam size of the laser light collided in the laser Compton scattering part is 5 μm.

  The electron beam collided in the laser Compton scattering part is preferably an electron beam having a normalized emittance of 10 μm-rad or less. This is because high-intensity radiation can be generated by using an electron beam having a small normalized emittance.

  The laser Compton scattering in the laser Compton scattering part is preferably performed in a range of 0 to 20 degrees in the collision angle between the polarized laser and the electron beam. This is because this range is preferable for increasing the collision probability of laser Compton scattering and generating quasi-monochromatic radiation. In the present invention, the collision angle is preferably in the range of 0 to 20 degrees. The collision angle can be adjusted by an electromagnet provided in front of the laser Compton scattering part.

The two-dimensional four-mirror resonator is preferably placed under vacuum in order to prevent laser scattering due to fine particles in the circulating optical path. The degree of vacuum is preferably 10 ⁻⁶ Pa or less.

  Furthermore, the present invention is accompanied by a polarization control unit that selectively controls right circular polarization or left circular polarization of laser light of a two-dimensional four-mirror optical system, and a resonance control unit D that causes resonance of each polarized laser. be able to.

  The polarization control unit is a system that detects the polarization state of the resonant laser. The system includes a plurality of plane mirrors for guiding laser light from an optical resonator to a predetermined distance away, a λ / 2 wavelength plate for adjusting the polarization plane of the laser light reflected by the last plane mirror, and the polarization plane is adjusted. Polarized beam splitter that separates the laser light into P-polarized light and S-polarized light, each pin photodiode that generates a polarization intensity signal indicating the laser intensity of each separated polarized beam, and each pin photodiode that is output A differential amplifier that calculates a difference between each polarization intensity signal and generates a differential signal, a zero-cross determiner that determines a difference signal output from the differential amplifier, and a zero-cross feedback that generates a zero-cross feedback signal from the determination result of the zero-cross determiner A signal generator, etc. Then, a processing board is provided that includes a microprocessor that performs various operations for performing this operation, or an LSI incorporating a calculation function.

  The resonance control unit is a system that controls a position adjusting means (piezo element) of a two-dimensional four-mirror optical system using a signal from the polarization control unit. The system resonates inside an optical resonator with a polarization changeover switch that receives a zero-cross feedback signal from the zero-cross feedback signal generator and outputs an instruction signal that specifies a right polarization or a left polarization to be selected. Based on the resonance monitor for measuring the intensity of the laser beam and the intensity of the laser beam from the laser light source unit, the output of the polarization changeover switch, the output of the resonance monitor, and the output of the zero cross feedback signal generator, the optical resonance A resonance controller for controlling the driving voltage of the piezoelectric element provided in the chamber. Then, a processing board is provided that includes a microprocessor that performs various operations for performing this operation, or an LSI incorporating a calculation function. The polarization controller uses a slight difference in optical path length between right polarized light and left polarized light.

  Furthermore, the present invention can be accompanied by a laser light source unit that supplies laser light. The laser light source unit includes a laser light source, a resonance matching unit, a plurality of plane mirrors for guiding laser light from the laser light source, a plurality of collimating lenses for adjusting the laser beam diameter, and a polarization beam splitter for making the laser linearly polarized light. ―, Etc. As the laser light source, a mode-locked laser oscillator, a pulse laser oscillator, a CW laser oscillator, or the like can be used. For example, a mode-locked laser oscillator that enables amplification by cooperative self-oscillation with a loop-shaped optical circuit formed of an optical resonator and a fiber laser amplifier is most preferable because it can supply high-intensity laser light.

  The resonance matching unit F is means for synchronizing the amplification of the laser beam in the two-dimensional four-mirror resonator with the amplification of the laser beam of the laser light source unit. The resonance matching means is effective when a mode-locked laser oscillator that enables amplification by cooperative self-oscillation is used as a laser light source in a loop-shaped optical circuit made up of an optical resonator and a fiber laser amplifier. The present invention equipped with the resonance matching unit makes it possible to easily amplify the mode-locked laser light of the optical resonator in the optical circuit of the mode-locked laser oscillator by the two-dimensional four-mirror resonator. This is because the amplified laser light naturally satisfies the resonance condition of the optical resonator in the optical circuit of the mode-locked laser oscillator by the resonance matching means. It has been confirmed that the resonance matching means can control the resonance width of 0.1０ without difficulty.

  The resonance matching unit detects a pulse signal of the laser light source unit and feeds it back to a two-dimensional four-mirror resonator, and reads a signal from the feedback detection system and an optical system of the two-dimensional four-mirror resonator A correction board for generating a drive control signal for driving the position control means. Then, it includes a processing board on which a microprocessor for performing various operations for implementing this, or an LSI such as an FPGA or an ASIC incorporating a calculation function is mounted.

As the feedback detection system, a polarization control unit C [λ / 2 mirror 17-polarized beam splitter (PBS) 14-S wave detection pin photodiode 18-P wave detection pin photodiode-differential as shown in FIG. A similar system can be used for amplifier 20—zero cross determiner 21—zero cross feedback signal generator 22] .

The correction as the board, can be used similar system in such resonant control unit D [polarization changeover switch 23-resonance monitoring 25-resonant controller 24 'as shown in FIG.

  Furthermore, the present invention can be accompanied by an electron beam generating unit that supplies a high-energy electron beam to a two-dimensional four-mirror resonator.

  The electron beam generating unit includes a high frequency signal generator and a high energy electron beam that emits a high energy electron beam by accelerating electrons using a high frequency voltage synchronized with a high frequency signal output from the high frequency signal generator. A generator. The high energy electron beam generator is preferably a radio frequency (RF) linear accelerator.

  Hereinafter, an aspect of the present invention will be described in detail as an embodiment (hereinafter also referred to as “the present embodiment”) with reference to the drawings.

The optical parameters of the two-dimensional four-mirror optical system used in the present invention shown in FIG. 1 are the distance L ₁ between the cylindrical concave mirrors, the distance (resonator length) L ₂ between the concave mirrors, the width d of the optical resonator, and the incident angle α. It is. These parameters are optimized so as to make the beam size (also referred to as beam waist) ω ₀ of the laser beam between the concave mirrors as small as possible. This is because the smaller the beam size, the larger the flux of laser Compton scattered X-rays, so that the flux can be increased by making ω ₀ as small as possible. In the present invention, a laser beam with λ = 1064 nm is used. L ₂ is preferably about 1075 mm from the resonance condition of the mode-locked laser. The value of ω ₀ was obtained from the relationship between the S-parameter and the laser size ω _{0 in} the vertical and horizontal directions of the concave mirror by performing envelope calculation using a beam expander in Gaussian beam optics. Here, the S-parameter is the position of the laser pulse in the laser direction along the other concave mirror from the one concave mirror in a pair of opposing concave mirrors. As a result, as shown in FIG. 5, it was found that the laser size ω ₀ converged to a minimum value of 5 μm when the S-parameter was 537.6 mm. It was also found that the resonance stable region, which is the overlapping of the relationship between the laser size and S-parameter in the vertical and horizontal directions of the concave mirror, is expanded as optics. The minimum value of the laser beam size is 50 μm, which is the minimum value of the laser beam size of a conventional high-intensity mode-locked oscillator (output 50 W, pulse duration 10 ps / pulse, wavelength 1064 nm, 150 MHz repetition). Therefore, the brightness of the laser beam generated by the optical resonator of the present invention should be 100 times higher than the brightness of the laser beam generated by the conventional high intensity mode oscillator. Is possible. Therefore, it is most preferable that the laser Compton scattering part is provided at a position of a half of the resonance length so that the beam size of the resonance laser is minimized. By doing so, the laser beam of the optical system is strengthened most in the laser Compton scattering part.

  As shown in FIG. 1, the width d of the optical resonator and the incident angle α of the laser light incident on the concave mirror are optimized so that the horizontal and vertical convergence forces of the concave mirror are maximized. In the present invention, the width d of the optical resonator is preferably about 240 mm, and the incident angle α is preferably about 0.20 radian (11.4 °).

  The present invention shown in FIG. 2 includes a pair of cylindrical concave mirrors 1 and 2 and a pair of concave mirrors 3 and 4 arranged in a two-dimensional manner, resonator length adjusting means 10 for adjusting the length of the optical path, laser light, A laser Compton scattering unit 7 that collides with an electron beam, a laser inlet 5 that introduces a laser beam emitted from a laser light source 11, an electron beam inlet 6 that introduces an electron beam, and a radiation outlet that extracts radiation Reference numeral 8 denotes a laser Compton scattered light resonator composed of the provided two-dimensional four-mirror resonator A. A part of the accumulated laser light in the optical resonator can be transmitted through the concave mirror 3 and emitted from the laser emission port 9 to the polarization control unit C described later.

  The present invention shown in FIG. 3 is an optical resonator including a two-dimensional four-mirror resonator A, a laser light source unit B, a polarization control unit C, and a resonance control unit D.

  The present invention shown in FIG. 4 is an optical resonator including a two-dimensional four-mirror resonator A, a laser light source unit B, a polarization control unit C, a resonance control unit D, and an electron beam generation unit E.

  Next, the operation of the present invention will be described with reference to FIGS.

The two-dimensional four-mirror resonator according to the present invention is placed under a vacuum of 10 ⁻⁶ Pa or less. When the start switch is turned on and the emission of laser light from the laser light source 11 is started, the polarization plane and beam diameter of the laser light are adjusted in the process of passing through the polarizing beam splitter 14 and the collimating lens 15, A laser that passes through the reflecting mirror 16 and enters the back side of the cylindrical concave mirror 1 of the two-dimensional four-mirror optical resonator and passes through the cylindrical concave mirror 1 becomes the cylindrical concave mirror 2 → the concave mirror 3 → the concave mirror 4 → the cylindrical concave mirror 1 → the cylindrical concave mirror 2. It is confined by the route.

  In parallel with this operation, the intensity of the laser beam transmitted through the cylindrical concave mirror 2 of the two-dimensional four-mirror resonator is measured by the resonance monitor 24 to generate a monitor signal and supplied to the resonance controller 25. The resonance monitor 24 includes a pin photodiode, and measures the intensity of the laser beam to generate a monitor signal (a signal having a large value when the laser beam in the two-dimensional optical resonator is resonating). Is.

  In parallel with these operations, the polarization control unit C reflects the laser light that has passed through the concave mirror 3 out of the laser light resonating in the two-dimensional four-mirror resonator, thereby two-dimensional four-mirror light. The plane of polarization of the laser light reflected by the plane mirror at the final stage is adjusted by adjusting the mounting angle according to the distance from the plurality of plane mirrors 16 and the two-dimensional four mirror optical resonators guided to a place away from the resonator by a predetermined distance. A λ / 2 wavelength plate 17, a polarization beam splitter 14 that separates laser light whose polarization plane is adjusted by the λ / 2 wavelength plate 17 into P-polarized light and S-polarized light, and S-polarized light separated by the polarizing beam splitter 14. A plane mirror 16 that reflects the laser beam on the side, a pin photodiode 18 that receives the S-polarized laser reflected by the plane mirror 16 and generates an S-polarized intensity signal indicating the laser intensity on the S-polarized side; A plane mirror 16 that reflects the P-polarized laser beam separated by the M-splitter 14 and a P-polarized laser beam reflected by the plane mirror are received, and a P-polarized intensity signal indicating the P-polarized laser intensity is received. A pin photodiode 19 to be generated; and a differential amplifier 20 that calculates a difference between an S-polarized light intensity signal output from the pin photodiode 18 and a P-polarized light intensity signal output from the pin photodiode 19 and generates a difference signal; It is determined whether the differential signal output from the differential amplifier 20 is zero-crossed, whether it is zero-crossed, whether it is zero-crossed from the plus side to the minus side, or zero-crossed from the minus side to the plus side, etc. And a zero-cross discriminator 21 for generating a zero-cross feedback signal indicating the result, and a two-dimensional four-mirror resonator The laser beam that has passed through the plane mirror among the laser beams that are resonating in is taken and separated into P-polarized light and S-polarized light, the intensity is measured, and the difference value is obtained, and the difference signal is zero-crossed. When a zero cross occurs, a zero cross feedback signal is generated by the zero cross signal generator 22 indicating whether the zero cross from the plus side to the minus side or the zero cross from the minus side to the plus side is generated, and sent to the polarization changeover switch 23 to resonate. Send to controller 25.

  In parallel with this operation, the resonance controller 25 generates a driving voltage having a ramp-like voltage value and supplies the driving voltage to the piezo element 10 in the two-dimensional four-mirror optical resonator. Is adjusted.

  In the instruction signal output from the polarization changeover switch 23, either right polarization or left polarization, for example, right polarization is designated, and in this situation, the right polarization is detected by the polarization control unit C. When a zero cross feedback signal is generated by the zero cross feedback signal generator 22 and a monitor signal indicating that the laser beam is resonating in the two-dimensional four-mirror optical resonator is output from the resonance monitor 24, the resonance controller This is detected by 25 and the voltage value of the drive voltage is fixed.

  As a result, the optical path length in the two-dimensional four-mirror resonator is fixed at that time, and the resonance for the right-polarized laser is maintained in the optical resonator for a specified time.

  The resonance controller 25 includes a microprocessor for performing various calculations, or a calculation board on which an LSI such as an FPGA or ASIC incorporating a calculation function is mounted, and an instruction signal output from the polarization changeover switch 23 Based on the monitor signal output from the resonance monitor 25 and the zero-cross feedback signal output from the zero-cross determination means C, a lamp-like voltage value or right-polarized or left-polarized laser light is selected in the two-dimensional optical resonator. By generating a drive voltage having a voltage value necessary for the generation and supplying it to the piezo element 10 in the two-dimensional optical resonator, the optical path length of the two-dimensional four-mirror optical resonator is controlled, and the two-dimensional optical resonator Are selectively accumulated with right-polarized light or left-polarized laser light.

  At this time, the line width of the pulse laser beam is determined by the mode-lock oscillation frequency and the time width of the pulse laser beam, and the beam size of the pulse laser beam at the collision point in the laser Compton scattering part of the two-dimensional four-mirror resonator. Therefore, if the time width of the pulse laser beam is within 30 psec, the pulse intensity at the laser Compton scattering part of the two-dimensional four-mirror resonator can be 1 mJ or more. At this time, if a pair of cylindrical concave mirrors of a two-dimensional four-mirror resonator and a mirror coated with a laser durable dielectric multilayer film are used as a pair of concave mirrors, laser Compton scattering of the two-dimensional four-mirror resonator is used. The pulse intensity at the part can be 10 mJ or more.

  Even when an instruction signal for alternately specifying right polarized light and left polarized light is output from the polarization changeover switch 23, the same control is performed, and the high intensity right polarized light is generated in the two-dimensional four-mirror resonator. The left polarized light is alternately amplified by resonance and accumulated in the optical resonator.

  The operation of the present invention will be described with reference to FIG.

  The high-energy electron beam generator 27 accelerates the electron beam using a high-frequency voltage synchronized with the high-frequency signal output from the high-frequency signal generator 26 and supplies the electron beam to the two-dimensional four-mirror resonator A. The high frequency signal generator 26 and the high energy electron beam generator 27 are in the electron beam generation unit. In parallel with this, the mode-locked laser generated by the laser light source unit B is supplied to the two-dimensional four-mirror resonator A. On the other hand, the polarization property is adjusted by the polarization control unit C, and the resonance state is adjusted by the resonance control unit D.

  A typical result obtained by the present invention will be described with reference to FIG.

The inventors of the present invention used an optical resonator as shown in FIG. 3 to extract a part of the laser beam in the two-dimensional four-mirror resonator, and observed the pulse intensity and the resonance state. As the laser light source, a mode-locked oscillator having a loop-shaped optical circuit connecting an optical resonator and a fiber laser amplifier was used. A concave mirror having a reflectivity of 99.99% was used as the resonant mirror of the two-dimensional four-mirror optical resonator. The pulse intensity of the seed laser put in the mode-locked oscillator was 0.1 μJ (= 10 ⁻⁷ J). The experimental results are shown in FIGS. FIG. 5 shows the result of measuring the relationship between the current of the excitation laser light source supplied to the optical circuit and the pulse intensity of the laser beam in the two-dimensional four-mirror resonator using a photodiode. From this result, it can be seen that the pulse intensity has reached about 1 millijoule. That is, the amplification factor was about 10,000 times. This indicates that a resonance width control of 0.1０ is achieved. FIG. 6 shows the result of observation of the resonance state of the laser beam in the two-dimensional four-mirror resonator with an oscilloscope. As can be seen from this result, the right polarized laser and the left polarized laser can be separated.

  In summary, the present inventions 1 to 4 can obtain a parallel beam having a perfect circular beam profile, and laser incident matching is very easy, and laser transmission matching is the same. Beam optics can be adjusted easily. As a result, it is possible to generate a polarized laser having a laser beam size of 30 μm or less and a pulse intensity of 1 millijoule or more with high industrial applicability.

  INDUSTRIAL APPLICABILITY The present invention is applicable to industrial applications related to polarized laser resonance methods, polarized radiation generation methods, X-ray source systems and devices that generate X-ray microbeams by laser Compton scattering, and in particular, medical equipment, diagnostic equipment, and materials. It can be widely used in many industries such as analyzers, structural analyzers, and material processing.

A two-dimensional four-mirror resonator B laser light source unit C polarization control unit D resonance control unit E electron beam generation unit F resonance matching unit 1 cylindrical concave mirror 2 cylindrical concave mirror 3 concave mirror 4 concave mirror 5 laser inlet 6 electron beam inlet 7 laser Compton scattering part 8 Radiation outlet 9 Laser light outlet 10 Resonance length adjusting means 11 Laser light source 12 Feedback control system 13 Correction board 14 Polarizing beam splitter 15 Collimating lens 16 Reflecting mirror 17 λ / 2 wavelength plate 18 Pin photodiode 19 Pin photo Diode 20 Differential amplifier 21 Zero cross determination device 22 Zero cross feedback signal generator 23 Polarization changeover switch 24 Resonance controller 25 Resonance monitor 26 High frequency signal generator 27 High energy electron beam generator

Claims (3)

A pair of cylindrical concave mirrors and a pair of concave mirrors arranged on a two-dimensional plane, a resonance length adjusting means for adjusting the length of the optical path, and a laser Compton scattering unit for colliding the laser beam with the electron beam are provided. Two-dimensional four-mirror optical system, a laser inlet for introducing laser light, an electron beam inlet for introducing an electron beam, and a radiation extraction port for extracting laser Compton scattered radiation are provided. a vessel, the two-dimensional 4 mirror light laser light introduced to the resonator from the laser introduction port, collisions among the electron beam introduced electron beam from the inlet port and the laser Compton scattering portion is performed laser A two-dimensional four-mirror resonator characterized by being strengthened most in the laser Compton scattering section so that Compton scattered X-rays can be extracted from a radiation extraction port. The polarization control unit for controlling the polarization of the two-dimensional 4 mirror optical resonator, and the two-dimensional 4 controls the cavity length adjusting means of the lens optical resonator resonating control unit further is provided, the polarization control unit and the resonance control 2. The laser beam according to claim 1, wherein the laser beam is separated into a right circularly polarized laser beam and / or a left circularly polarized laser beam in accordance with the length of the optical path and amplified through a unit. Dimensional four mirror optical resonator.   A mode-locked laser oscillator that supplies a mode-locked laser, and a laser light source unit that includes a resonance matching unit that matches the resonance state of the two-dimensional four-mirror resonator and the resonance state of the mode-locked laser oscillator. 3. The two-dimensional four-mirror resonator according to claim 2, wherein the supplied laser beam is stably amplified.