JP2012093675A - Polarized beam conversion element, polarized beam conversion method, electron gun, beam measurement device, and electron generation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarized beam conversion element capable of converting a polarized beam into a polarization beam whose division number is large at a low cost, a polarized beam conversion method using the same, an electron gun, a beam measurement device, and an electron generation method.SOLUTION: In the polarized beam conversion element according to an embodiment of the invention, a first wavelength plate 10 is provided with four divided regions 11-14, λ/8 plates are provided to the respective divided regions 11-14, and axis azimuths of the λ/8 plates are substantially orthogonal in two adjacent divided regions and substantially parallel in two opposite divided regions. A second wavelength plate 20 is provided with four divided regions 21-24, λ/4 plates are provided to the respective divided regions 21-24, and axis azimuths of the λ/4 plates are substantially orthogonal in the two adjacent divided regions and substantially parallel in the two opposite divided regions. The respective divided regions are arranged in a shifted state, and the axis azimuths of the λ/8 plate and λ/4 plate shift.

Description

  The present invention relates to a polarization beam conversion element, a polarization beam conversion method, an electron gun, a beam measurement device, and an electron generation method, and more particularly, to a polarization beam conversion element and polarization for generating pseudo radial polarization and pseudo azimuth polarization. The present invention relates to a beam conversion method, an electron gun using the same, and an electron generation method.

A radial polarized beam is used for increasing the brightness of an electron gun, increasing the efficiency of laser processing, measuring molecular orientation in a laser microscope, and the like (for example, Patent Documents 1 to 3). The radial polarization beam is generated by making a laser beam incident on a polarization element. As a polarizing element, an element combining a wave plate (phase plate) manufactured from an optical crystal having anisotropy such as quartz (hereinafter referred to as a combined wave plate element), a photonic crystal element, an element using liquid crystal, etc. Has been put to practical use. Of these, in the case of using a combined wave plate element and a photonic crystal element, not a complete radial polarization beam, but a pseudo radial polarization beam (the cross section of the beam is divided into a plurality of regions. A beam that is linearly polarized in the radial direction).
In Patent Document 2, pseudo radial polarization is used for a beam measuring apparatus and a beam measuring method. Specifically, an electro-optic element having a hollow portion through which the electron beam passes is disposed in the electron beam path. The crystal axis orientation of the electro-optic element changes due to the electric field generated by the electron beam. The polarization state changes as the pseudo radial polarization passes through the electro-optic element. For this reason, the spatial distribution of the electron beam can be measured by measuring the polarization state of the light that has passed through the electro-optic element. Moreover, in patent document 1, Z polarized light is produced | generated by condensing pseudo radial polarized light.

JP 2008-288099 A JP 2008-288087 A JP 2010-015877 A

  The combined wave plate element has an advantage that it can cope with a wide wavelength from ultraviolet to infrared and is hardly damaged even when a high-intensity laser is used. On the other hand, in the generation of the pseudo-radial polarized beam, if an attempt is made to increase the number of divisions of a region, it is necessary to cut out a wave plate having various axial directions into a complicated shape, which makes it difficult to manufacture.

For example, in the case of four divisions, the central angle of each divided region is 90 °, but in the case of eight divisions, the central angle of each divided region is 45 °. When an 8-divided combination wave plate element is produced, it becomes difficult to cut out the wave plate. When the central angle is 45 °, it is difficult to cut out compared to when the central angle is 90 °. Furthermore, in order to make each divided region have a predetermined axial orientation, it is necessary to prepare wave plates having various axial orientations. For this reason, the number of parts required for preparation increases and manufacturing cost will increase. The above problem also occurs in the combination wave plate for generating pseudo azimuth polarized light. As described above, there is a problem that it is necessary to prepare a wavelength plate having the same number of divisions as that of pseudo radial polarization or pseudo azimuth polarization. Therefore, it is necessary to divide the wave plate by the same number as that of the pseudo radial polarization or the pseudo azimuth polarization. Therefore, there is a problem that the number of divisions of the wave plate increases and the manufacturing cost increases.
The present invention has been made in view of the above-described problems, and a polarization beam conversion element having a greater number of divisions than the number of divisions of a wave plate, a polarization beam conversion method using the same, an electron gun, a beam measurement device, and an electron The purpose is to provide a generation method.

A polarization beam conversion element according to a first aspect of the present invention is a polarization beam conversion element that includes first and second wave plates, and generates pseudo radial polarization or pseudo azimuth polarization. The wavelength plate is provided with divided regions that are radially divided by 2 ⁿ (n is a natural number of 2 or more), and (λ / 4) × (1-arccos (0.5 / cos ( A divided wave plate that provides a phase difference of π / 2 ⁿ )) / (π / 2)) is provided, and the axial direction of the divided wave plate of the first wave plate is rotationally symmetric, The second wave plate disposed after the wave plate of 1 is provided with ^2n- divided divided areas, each of which is (λ / 4) × (arccos (1-0). .5 / cos ² (π / 2 ⁿ )) / (π / 2)) phase difference wave A long plate is provided, and the axial direction of the divided wave plate of the second wave plate is rotationally symmetric, and each of the divided regions of the first wave plate is divided of the second wave plate. The axial direction of the divided wave plate provided on the first wave plate is shifted from the axial direction of the divided wave plate of the second wave plate. Therefore, it is possible to provide a polarization beam conversion element that can convert into a beam having a larger number of divisions than the number of divisions of the wave plate at a low cost.

Polarized beam conversion device according to a second aspect of the present invention, the above a polarized beam conversion element, wherein the first wave plate, and the rotation symmetry of at least one of 2 [pi / 2 ⁿ of the second wave plate It is characterized by being. Thereby, it can be brought close to radial polarization or azimuth polarization.

A polarization beam conversion element according to a third aspect of the present invention is the polarization beam conversion element described above, and is disposed so as to coincide with a divided region of the second wave plate in a plane perpendicular to the optical axis. A phase plate having ⁿ divided regions is further provided, and an optical path length difference corresponding to λ / 2 ⁿ is provided in a divided region adjacent to the phase plate. Thereby, a non-Laguerre Gaussian beam can be converted into pseudo radial polarization or pseudo azimuth polarization.

A polarization beam conversion element according to a fourth aspect of the present invention is the polarization beam conversion element described above, wherein the axial direction of the divided wave plate of the first wave plate and the divided wave plate of the second wave plate Is shifted by approximately π / 2 ⁿ . Thereby, it can be made closer to pseudo radial polarization or pseudo azimuth polarization.

A polarization beam conversion element according to a fifth aspect of the present invention is the polarization beam conversion element described above, wherein a boundary line between the division regions of the first wave plate and the division region of the second wave plate. Is deviated by approximately π / 2 ⁿ . Thereby, it can be made closer to pseudo radial polarization or pseudo azimuth polarization.

  A polarization beam conversion element according to a sixth aspect of the present invention is the polarization beam conversion element described above, wherein n = 2, the four divided regions of the first wave plate, and the second wave plate Each of the four divided areas is rectangular. Thereby, the 1st and 2nd wavelength plate can be created easily.

  A polarization beam conversion element according to a seventh aspect of the present invention is the polarization beam conversion element described above, further including a third wavelength plate disposed in a stage preceding the first wavelength plate, and the third wavelength plate. The wave plate converts incident linearly polarized light into circularly polarized light. Thereby, linearly polarized light can be converted into pseudo radial polarized light or pseudo azimuth polarized light.

  A polarization beam conversion element according to an eighth aspect of the present invention is a polarization beam conversion element that includes first and second wavelength plates, and generates pseudo radial polarization or pseudo azimuth polarization. The wavelength plate is provided with divided regions that are radially divided into two, a λ / 4 plate is provided in each of the divided regions, and the axial orientation of the λ / 4 plate of the first wavelength plate is The second wave plate, which is substantially orthogonal and provided at the subsequent stage of the first wave plate, is provided with divided regions that are radially divided into two, and a λ / 4 plate is provided in each of the divided regions. Provided, the axial direction of the λ / 4 plate of the first wave plate is substantially orthogonal, and each of the divided regions of the first wave plate is shifted from the divided region of the second wave plate It is what has been. Thereby, it is possible to provide a polarization beam conversion element that can convert the beam into four-divided beams at low cost.

  A polarization beam conversion element according to a ninth aspect of the present invention is the polarization beam conversion element described above, wherein a boundary line of the divided region of the first wave plate in the plane perpendicular to the optical axis, and the first A phase plate having four divided regions divided by two boundary lines that coincide with the boundary line of the divided region of the wavelength plate, and an optical path length corresponding to λ / 4 in the divided region adjacent to the phase plate It gives a difference. Thereby, a non-Laguerre Gaussian beam can be converted into pseudo radial polarization or pseudo azimuth polarization.

  A polarization beam conversion element according to a tenth aspect of the present invention is the polarization beam conversion element described above, wherein the phase plate and the second wavelength plate are integrally formed. is there. Thereby, the number of parts can be reduced, and the part cost can be reduced.

  A polarization beam conversion element according to an eleventh aspect of the present invention is the polarization beam conversion element described above, wherein the phase plate is configured by a vapor deposition film deposited on the second wavelength plate, and the second wavelength. The phase plate is formed by evaporating the same material as that of the plate. Thereby, the utilization efficiency of light can be improved.

  A polarization beam conversion element according to a twelfth aspect of the present invention is the polarization beam conversion element described above, wherein the axial direction of the λ / 4 plate of the first wavelength plate and the second wavelength plate are The axial direction of λ / 4 is parallel. Thereby, it can be made closer to pseudo radial polarization or pseudo azimuth polarization.

  A polarization beam conversion element according to a thirteenth aspect of the present invention is the polarization beam conversion element described above, wherein a boundary line of the division region of the first wave plate and the division region of the second wave plate Is deviated by approximately π / 2. Thereby, it can be made closer to pseudo radial polarization or pseudo azimuth polarization.

A polarization beam conversion method according to a fourteenth aspect of the present invention is a polarization beam conversion method for generating pseudo-radial polarization or pseudo-azimuth polarization, wherein circularly polarized light is incident on a first wave plate, The light having passed through the first wave plate is incident on the second wave plate, and the first wave plate has a divided region that is radially divided by 2 ⁿ (n is a natural number of 2 or more). Each of the divided regions is provided with a divided wave plate that gives a phase difference of (λ / 4) × (1-arccos (0.5 / cos (π / 2 ⁿ )) / (π / 2)). The axial direction of the divided wave plate of the first wave plate is rotationally symmetric, and the second wave plate disposed at the subsequent stage of the first wave plate is divided into 2 ⁿ radially. Divided areas are provided, and each of the divided areas is (λ / 4) × ^{arccos (1-0.5 / cos 2 (π} / 2 n)) / (π / 2)) divided wave plate providing a phase difference is provided in the axial direction of the divided wave plate of the second wave plate Is a rotationally symmetric, and each of the divided regions of the first wave plate is shifted from the divided region of the second wave plate, and is provided on the first wave plate And the axial direction of the divided wave plate of the second wave plate are deviated. Therefore, it is possible to generate a beam having a larger number of divisions than the number of divisions of the wave plate at low cost.

  A polarization beam conversion method according to a fifteenth aspect of the present invention is a polarization beam conversion method for generating pseudo-radial polarization or pseudo-azimuth polarization, wherein circularly polarized light is incident on a first wave plate; The light having passed through the first wave plate is incident on the second wave plate, and the first wave plate is provided with a divided region that is radially divided into two, A λ / 4 plate is provided for each, the axial direction of the divided wave plate of the first wave plate is substantially rotationally symmetric, and a second wavelength provided after the first wave plate The plate is provided with a divided region that is radially divided into two, a λ / 4 plate is provided in each of the divided regions, and the axial direction of the divided wave plate of the first wave plate is substantially rotated. Each of the divided regions of the first wave plate is symmetrical. However, this is shifted from the divided region of the second wave plate. Thereby, it is possible to provide a polarization beam conversion element that can convert the beam into four-divided beams at low cost.

  According to a sixteenth aspect of the present invention, there is provided an electron gun comprising: the polarizing beam converting element; a lens for condensing the pseudo radial polarized light generated by the polarizing beam converting element; and the light condensed by the lens is incident A photocathode. Thereby, a high-quality electron beam can be generated.

  According to a seventeenth aspect of the present invention, there is provided a photocathode comprising a step of causing circularly polarized light to enter the polarizing beam converting element, and condensing the pseudo-radial polarized light generated by the polarizing beam converting element. And the step of making it enter. Thereby, a high-quality electron beam can be generated.

  An electron gun according to an eighteenth aspect of the present invention is a beam measuring device 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. A light source unit that shapes and emits a pulse waveform of the pulse laser beam so as to change, a delay element that gives a time delay corresponding to an incident position with respect to the pulse laser beam emitted from the light source unit, and the pulse laser beam A polarization beam conversion element that converts the polarization state into a different polarization state according to the incident position, an electro-optic element that is disposed in the beam path of the quantum beam and has a different crystal axis according to the incident position, A polarizer for extracting a predetermined polarization component from pulse laser light incident from the incident optical system via the electro-optic element, and a pulse laser extracted by the polarizer. Comprising a measuring device for measuring the spectrum of the laser light, and the polarized beam conversion element, in which the polarization beam conversion element is used according to any one of claims 1 to 8. Thereby, three-dimensional measurement can be performed with high accuracy.

  According to the present invention, it is possible to provide a polarization beam conversion element capable of converting into a beam having a greater number of divisions than the number of divisions of the wave plate, a polarization beam conversion method using the same, an electron gun, and an electron generation method. it can.

1 is a side view showing a configuration of a polarization beam conversion element according to a first embodiment. It is a front view which shows the structure of the 1st wavelength plate used for a polarization beam conversion element. It is a front view which shows the structure of the 2nd wavelength plate used for a polarization beam conversion element. It is a front view which shows the structure of the phase plate used for a polarization beam conversion element. It is a top view which shows arrangement | positioning of the incident light on a 1st wavelength plate. It is a figure which shows the polarization state of the light which passed the 1st wavelength plate. It is a top view which shows arrangement | positioning of the incident light on a 2nd wavelength plate. It is a figure which shows the polarization state of the light which passed the 2nd wavelength plate. It is a figure which shows the phase difference of the light which passed the 2nd wavelength plate. It is a figure which shows the structure for changing right circularly polarized light into pseudo radial polarized light. It is a figure which shows the structure for changing left circularly polarized light into pseudo radial polarized light. FIG. 6 is a side view showing a configuration of a polarization beam conversion element according to a second embodiment. It is a front view which shows the structure of the 3rd wavelength plate used for a polarization beam conversion element. FIG. 6 is a side view showing a configuration of a polarization beam conversion element according to a third embodiment. FIG. 6 is a side view showing the configuration of a polarization beam conversion element according to a fourth embodiment. It is a figure which shows the structure of the electron gun using a polarization beam conversion element. It is a figure which shows the structure of the beam measuring apparatus using a polarization beam conversion element. It is a perspective view which shows a Poincare sphere. It is a front view which shows the 1st wavelength plate of 8 divisions. It is a front view which shows the 2nd wavelength plate of 8 divisions. It is the projection figure which looked at Poincare sphere from the north pole side. It is the projection figure which looked at Poincare sphere from the north pole side. It is a front view which shows the structure of the 1st wavelength plate used when producing | generating a 4-part dividing beam. It is a front view which shows the structure of the 2nd wavelength plate used when producing | generating a 4-part dividing beam. It is a front view which shows the structure of the phase plate used when producing | generating a 4-part dividing beam.

Embodiment 1
Embodiments of the present invention will be described below with reference to the drawings. First, the overall configuration of the polarization beam converting element according to the present embodiment will be described with reference to FIG. FIG. 1 is a side view showing the overall configuration of the polarization beam converting element. The polarization beam conversion element 1 includes a first wave plate 10, a second wave plate 20, and a phase plate 30. By combining the first wave plate 10, the second wave plate 20, and the phase plate 30, the polarization beam conversion element 1 is formed. The polarization beam conversion element 1 is an element for generating pseudo radial polarization (hereinafter also simply referred to as radial polarization) or pseudo azimuth polarization (hereinafter also simply referred to as azimuth polarization). A first wave plate 10 is provided after the phase plate 30. A second wave plate 20 is provided after the first wave plate 10. Therefore, the incident light that has passed through the phase plate 30 enters the first wave plate 10. Incident light that has passed through the first wave plate 10 enters the second wave plate 20. Each of the first wave plate 10 and the second wave plate 20 is a combined wave plate element in which wave plates are combined. Each of the first wave plate 10 and the second wave plate 20 has a parallel light incident surface and a light emitting surface, and the light incident surface and the light emitting surface are perpendicular to the optical axis. Is arranged.

  The laser beam is a parallel light beam and propagates parallel to the optical axis. A description will be given using a three-dimensional orthogonal coordinate system in which the propagation direction of the laser beam is the Z direction, the vertical direction in FIG. 1 is the Y direction, and the direction perpendicular to the paper surface of FIG. When the right circularly polarized laser light passes through the polarization beam converting element 1, it is changed to pseudo radial polarization. When the amplitude of the electric vector of right circularly polarized light is 1, the electric vectors Ex and Ey in the X direction and the Y direction are expressed by the following formula (1).

Ex = cos (−ωt + π / 2)
Ey = cos (−ωt) (1)

  Next, the configuration of the first wave plate 10 will be described with reference to FIG. FIG. 2 is a plan view showing the configuration of the first wave plate 10. As shown in FIG. 2, the first wave plate 10 has four divided regions 11 to 14. For example, four divided regions 11 to 14 are formed by radially dividing the first wave plate 10 into four equal parts. Since the external shape of the first wave plate 10 is square, each of the divided regions 11 to 14 is also square. The four divided areas 11 to 14 are squares having the same size. The center of the first wave plate 10 coincides with the optical axis. The four sides of the outer shape of the first wave plate 10 are inclined 45 ° or −45 ° from the X axis or the Y axis. The four divided regions 11 to 14 are arranged along the circumferential direction around the optical axis. The four divided areas 11 to 14 are defined as a first divided area 11, a second divided area 12, a third divided area 13, and a fourth divided area 14, respectively.

  In the following description, the optical axis, that is, the center of the first wave plate 10 is the origin of the XY plane, and the angle is 0 ° on the + X axis and positive in the counterclockwise direction when viewed from the incident side. The first divided area 11 and the third divided area 13 are arranged on the Y axis, and the second divided area 12 and the fourth divided area 14 are arranged on the X axis. The first divided region 11 and the third divided region 13 are arranged in line symmetry with respect to the X axis, and the second divided region 12 and the fourth divided region 14 are arranged in line symmetry with respect to the Y axis. Yes. The first divided area 11 and the third divided area 13 are arranged opposite to each other with the origin interposed therebetween, and the second divided area 12 and the fourth divided area 14 are arranged to face each other across the origin. The first wave plate 10 is arranged so that the diagonal line of the first wave plate 10 is parallel to the X direction and the Y direction.

  Each of the divided regions 11 to 14 has a λ / 8 plate. In FIG. 2, the axis direction of the λ / 8 plate (the direction of the optical axis in the XY plane) is indicated by an arrow. In the following description, the axial direction is the direction of the slow axis of the wave plate. The axial direction of the λ / 8 plate provided in the first divided region 11 and the third divided region 13 is + 45 °, and the axis of the λ / 8 plate provided in the second divided region 12 and the fourth divided region 14 The azimuth is −45 ° (315 °). Accordingly, among the four divided regions 11 to 14, the axial orientations of the λ / 8 plates provided in the two divided regions facing each other are parallel. For example, the axial directions (+ 45 °) of the λ / 8 plates provided in the first divided region 11 and the third divided region 13 are parallel. Similarly, the axial directions (−45 °) of the λ / 8 plates provided in the second divided region 12 and the fourth divided region 14 are parallel to each other. In addition, the axial orientations of the λ / 8 plates provided in the two divided regions adjacent to each other in the circumferential direction among the four divided regions 11 to 14 are orthogonal to each other. For example, the axial orientation (+ 45 °) of the λ / 8 plate in the first divided region 11 is orthogonal to the axial orientation (−45 °) of the λ / 8 plate in the second divided region 12 and the fourth divided region 14. Yes. Similarly, the axial orientation (+ 45 °) of the λ / 8 plate in the third divided region 13 is orthogonal to the axial orientation (−45 °) of the λ / 8 plate in the second divided region 12 and the fourth divided region 14. ing.

  The boundary line between the first divided region 11 and the second divided region 12 and the boundary line between the third divided region 13 and the fourth divided region 14 are straight lines of + 45 ° passing through the origin, and the first divided region 11 and the third divided region This is parallel to the axial direction of the λ / 8 plate provided in the divided region 13. The boundary line between the first divided region 11 and the fourth divided region 14 and the boundary line between the third divided region 13 and the second divided region 12 are −45 ° straight lines passing through the origin, and the second divided region 12 and the fourth divided region 12 This is parallel to the axial direction of the λ / 8 plate provided in the divided region 14.

  Next, the configuration of the second wave plate 20 will be described with reference to FIG. FIG. 3 is a front view showing the configuration of the second wave plate 20. The second wave plate 20 also has four divided regions 21 to 24. Here, the second wave plate 20 has the same size as the first wave plate 10. Since the outer shape of the second wave plate 20 is square, each of the divided regions 21 to 24 is also square. The divided areas 21 to 24 are squares having the same size. The center of the second wave plate 20 coincides with the optical axis. The four divided regions 21 to 24 are arranged along the circumferential direction with the optical axis as the center. The four divided areas 21 to 24 are defined as a first divided area 21, a second divided area 22, a third divided area 23, and a fourth divided area 24, respectively. The four sides of the second wave plate 20 are parallel to the X direction or the Y direction.

  In the XY plan view, the divided regions 21 to 24 of the second wave plate 20 are arranged so as to be shifted by 45 ° with respect to the divided regions 11 to 14 of the first wave plate 10. Therefore, the boundary line between the first divided region 21 and the second divided region 22 and the boundary line between the third divided region 23 and the fourth divided region 24 are straight lines that pass through the origin and are parallel to the Y axis. A boundary line between the first divided region 21 and the fourth divided region 24 and a boundary line between the third divided region 23 and the second divided region 22 are straight lines that pass through the origin and are parallel to the X axis. In the XY plane, the first divided area 21 is arranged in the second quadrant, the second divided area 22 is arranged in the first quadrant, the fourth divided area 24 is arranged in the third quadrant, and the third divided area 23 is Arranged in 4 quadrants.

  Each of the divided regions 21 to 24 has a λ / 4 plate. Here, the axis direction of the λ / 4 plate (the direction of the optical axis in the XY plane) is indicated by an arrow. The axis direction of the λ / 4 plate provided in the first divided region 11 and the third divided region 13 is + 90 °, and the axis of the λ / 4 plate provided in the second divided region 22 and the fourth divided region 24 The azimuth is 0 °. Therefore, among the four divided areas 21 to 24, the axial directions of the λ / 4 plates provided in two opposed divided areas are parallel to each other. For example, the axial directions (+ 90 °) of the λ / 4 plates provided in the first divided region 21 and the third divided region 23 are parallel. Similarly, the axial directions (+ 90 °) of the λ / 4 plates provided in the second divided region 12 and the fourth divided region 24 are parallel to each other. In addition, the axial orientations of the λ / 4 plates provided in the two divided regions adjacent in the circumferential direction among the four divided regions 21 to 24 are orthogonal to each other. For example, the axial orientation (+ 90 °) of the λ / 4 plate in the first divided region 21 is orthogonal to the axial orientation (0 °) of the λ / 4 plate in the second divided region 22. Similarly, the axial orientation (+ 90 °) of the λ / 4 plate in the third divided region 23 is orthogonal to the axial orientation (0 °) of the λ / 4 plate in the fourth divided region 24.

  Next, the configuration of the phase plate 30 will be described with reference to FIG. FIG. 4 is a front view showing the configuration of the phase plate 30. Similarly to the second wave plate 20, the phase plate 30 also has four divided regions 31 to 34. The outer shape of the phase plate 30 is a square having substantially the same size as the second wave plate. Since the outer shape of the phase plate 30 is square, the divided regions 31 to 34 are also square. The divided regions 31 to 34 are arranged so as to coincide with the divided regions 21 to 24 of the second wave plate 20 in the XY plan view. That is, the first divided area 31 is arranged in the second quadrant, the second divided area 32 is arranged in the first quadrant, the fourth divided area 34 is arranged in the third quadrant, and the third divided area 33 is arranged in the fourth quadrant. Placed in.

  The phase plate 30 is made of a transparent material (for example, glass or resin), and has a different thickness according to the position on the XY plane. Thereby, the phase can be shifted according to the incident position, and the wavefront of the laser beam can be adjusted. Specifically, the thickness of the first divided region 31 to the fourth divided region 34 is changed so that the optical path length differs by λ / 4. Assuming that the first divided region 31 is the reference (0), the second divided region 32 is thicker than the first divided region 31 to correspond to the optical path length of λ / 4. The third divided region 33 is thicker corresponding to the optical path length of λ / 2, and the fourth divided region 34 is thicker corresponding to the optical path length of (3/4) λ. Accordingly, the thickness of the phase plate 30 changes in a spiral staircase shape. The light that has passed through the fourth divided region 34 has a wavefront delayed by 3 / 4λ compared to the light that has passed through the first divided region 31. That is, the phase of the light that has passed through the fourth divided region 34 is delayed by 3π / 2 compared to the light that has passed through the first divided region 31. Similarly, the light that has passed through the third divided region 33 has a wavefront delayed by λ / 2 compared to the light that has passed through the first divided region 31, and the light that has passed through the second divided region 32 has Compared to the light passing through 31, the wavefront is delayed by λ / 4. That is, the light that has passed through the third divided region 33 is delayed in phase by π compared to the light that has passed through the first divided region 31, and the light that has passed through the second divided region 32 has passed through the first divided region 31. The phase is delayed by π / 2 compared to the light that has been emitted. By using the phase plate 30, the wavefront of the laser beam that has passed can be delayed without changing the polarization state. The difference in thickness of the phase plate 30 can be determined by the wavelength of the laser light and the refractive index of the material constituting the phase plate 30.

  The polarization state of the laser light that has passed through the first wave plate 10 will be described with reference to FIGS. 5 and 6. FIG. 5 is a diagram showing the axial directions of the divided regions 11 to 14, and FIG. 6 is a diagram for explaining the polarization state of the laser light that has passed through the first wave plate 10. As shown in FIG. 5, it is assumed that a laser beam having a circular spot shape is incident on the first wave plate 10. The center of the laser beam spot coincides with the center of the first wave plate 10. Then, ¼ of the spot passes through the first divided region 11. Similarly, the light passing through the second divided region 12, the third divided region 13, and the fourth divided region 14 is also ¼ of the spot.

  The first divided area 11 to the fourth divided area 14 are composed of λ / 8 plates. The laser beam is right circularly polarized light. Accordingly, when right circularly polarized light passes through the divided regions (first divided region 11 and third divided region 13) having an axis orientation of + 45 °, elliptically polarized light having a major axis in the Y direction as shown in FIG. It becomes. When right circularly polarized light passes through the divided regions (the second divided region 12 and the fourth divided region 14) having an axis orientation of −45 °, the light becomes elliptically polarized light having the major axis in the X direction. Thus, the polarization state of incident light changes according to the incident position on the first wave plate 10.

  Then, the incident light that has passed through the first wave plate 10 enters the second wave plate 20. As described above, the second wave plate 20 has four divided regions 21 to 24. As shown in FIG. 7, the center of the incident light spot and the center of the second wave plate 20 coincide. Then, the divided regions 11 to 14 of the first wave plate 10 and the divided regions 21 to 24 of the second wave plate 20 are arranged apart from each other. Therefore, incident light that has passed through the first divided region 11 of the first wave plate 10 enters the first divided region 21 and the second divided region 22 of the second wave plate 20. Incident light that has passed through the second divided region 12 of the first wave plate 10 enters the third divided region 23 and the second divided region 22 of the second wave plate 20. Incident light that has passed through the third divided region 13 of the first wave plate 10 enters the third divided region 23 and the fourth divided region 24 of the second wave plate 20. Incident light that has passed through the fourth divided region 14 of the first wave plate 10 enters the first divided region 21 and the fourth divided region 24 of the second wave plate 20.

  Therefore, the emitted light that has passed through the first wave plate 10 and the second wave plate 20 is in an 8-divided polarization state as shown in FIG. Here, the description will be made assuming that the emitted light is divided into eight regions 51 to 58. The numbers described in the respective areas 51 to 58 indicate the axial directions of the λ / 8 plate in the first wave plate 10 and the λ / 4 plate in the second wave plate 20. For example, the outgoing light in the region 51 passes through a λ / 8 plate with an axial direction of −45 ° and a λ / 4 plate with an axial direction of 90 °. The axial direction of the portion where the outgoing light of the region 51 passes is expressed as (−45, 90). Similarly, the region 52 is (45,90), the region 53 is (45,0), the region 54 is (−45,0), the region 55 is (−45,90), and the region 56 is (45,90). ), The region 57 is (45,0), and the region 58 is (−45,0).

  In two regions facing each other across the origin, the axial directions are the same. For example, the axial orientations of the region 51 and the region 55 are (−45, 90). Similarly, the axial orientations of the regions 52 and 56 are (45,90), the axial orientations of the regions 53 and 57 are (45,0), and the axial orientations of the regions 54 and 58 are (−45,0). It has become. As described above, the axial orientations coincide with each other in the pair of regions facing each other. Further, since the regions 51 to 54 have different axial orientations, there are four types of axial orientations (45,90), (−45,90), (45,0), and (−45,0). .

  The polarization axis in each region is radial. That is, the polarization state is linearly polarized light that faces the radial direction from the center in each of the eight regions. In FIG. 8, the polarization direction of the emitted light is shown outside the circular spot. The region 51 and the region 55 having the same axial orientation are linearly polarized light having a polarization axis of 157.5 ° (−22.5 °). Similarly, the region 52 and the region 56 are linearly polarized light having a polarization axis of 112.5 ° (−67.5 °), and the region 53 and the region 57 are linearly polarized light having a polarization axis of 67.5 °. The region 58 is linearly polarized light having a polarization axis of 22.5 °. Therefore, in the eight-divided regions 51 to 58, the outgoing light is radially arranged with the polarization axis. The polarization axis indicates the direction of the polarization plane in the XY plane. As described above, in two regions facing each other across the optical axis, the polarization axes are parallel, and in adjacent regions, the polarization axes are different by 45 °.

  Further, when passing through the first wave plate 10 and the second wave plate 20, the phase changes according to the position in the XY plane. Therefore, the wavefront of the outgoing light is delayed, and the wavefront shifts. Here, the phase delay of the emitted light will be described with reference to FIG. When the phase of the emitted light from the region 51 and the region 52 is used as a reference, the phase of the emitted light from the region 53 and the region 54 is advanced by π / 2, and the phase of the emitted light from the region 55 and the region 56 is advanced by π. The phase of the emitted light from the regions 57 and 58 is 3π / 2 earlier, that is, π / 2 slower. For this reason, considering a certain XY plane, the magnitude of the electric vector changes according to the phase. Furthermore, when considering a certain XY plane, the directions of the electric vectors coincide in two opposing regions. For example, the direction of the electric vector in the region 51 coincides with the direction of the electric vector in the region 55 (+ 157.5 °).

  Therefore, the phase plate 30 is used to align the phases. As described above, the phase plate 30 has different thicknesses in the divided regions 31 to 34. For this reason, when the region 51 and the region 52 are used as a reference, the phase is delayed in advance by π / 2 in the region 53 and the region 54 by the phase plate 30. Similarly, by the phase plate 30, the region 55 and the region 56 are in a state in which the phase is previously delayed by π, and the region 57 and the region 58 are in a state in which the phase is previously delayed by 3π / 2. Accordingly, the phases of the emitted light that has passed through the phase plate 30, the first wave plate 10, and the second wave plate 20 are aligned. Thereby, the right circularly polarized light becomes pseudo radial polarized light. In this way, by combining the four-divided phase plate, eight-divided pseudo radial polarization can be generated.

  Next, a method for creating the first wave plate 10 and the second wave plate 30 will be briefly described. When the first wave plate 10 is formed, a square λ / 8 plate is prepared. The axis direction of the λ / 8 plate is parallel to one side of the square. Then, the λ / 8 plate is divided into four equal parts. That is, in order to form four divided regions, the λ / 8 plate is cut out along two dividing lines passing through the center of the square λ / 8 plate. The two dividing lines are orthogonal to each other, and are parallel or perpendicular to the four sides of the λ / 8 plate. And the division | segmentation piece cut out into four is fixed using a holder, a transparent substrate, etc. At this time, the λ / 8 plate cut into four pieces is fixed so that the axial direction is as shown in FIG. For example, two λ / 8 plates corresponding to two opposing divided regions are rotated by 90 ° and fixed.

  Here, when the λ / 8 plate is cut, the center angle can be cut to 90 °. For this reason, it is not necessary to cut out into a complicated shape, and cutting out can be performed easily and reliably. That is, it can be easily cut out as compared with the case of eight pieces having a central angle of 45 °. Furthermore, one first wave plate 10 can be formed by four pieces cut out from one λ / 8 plate. Thereby, the number of parts can be reduced and the manufacturing cost can be reduced. Similarly, the second wave plate 30 can be created by cutting out a λ / 4 plate. In this way, the cutting can be performed easily and reliably, and the productivity can be improved. Further, one second wave plate 20 can be formed by four pieces cut out from one λ / 4 plate. As a result, it is not necessary to prepare λ / 4 plates and λ / 8 plates having different axial orientations, and the number of components can be reduced. Thus, the manufacturing cost can be reduced, and the polarization beam conversion element 1 for generating pseudo radial polarization and pseudo azimuth polarization can be realized at low cost.

  Also, the first wave plate 10 can be created by preparing four λ / 8 plates having the same shape and combining the four λ / 8 plates. For example, four square-shaped or sector-shaped λ / 8 plates having a central angle of 90 ° are prepared. Then, as in the case of cutting into four sheets, four λ / 8 plates are combined. By doing in this way, it becomes possible to produce the 1st wavelength plate 10 using the same-shaped (lambda) / 8 plate. Similarly, the second wavelength plate 20 can be created by preparing four λ / 4 plates. In this case, since there is no need to cut out and the same parts need only be prepared, the first wave plate 10 and the second wave plate 20 can be produced at a lower cost.

The first wave plate 10 and the second wave plate 20 are rotationally symmetric by making the central angles of the four divided regions perpendicular to each other. That is, in the adjacent divided regions, the axis directions are shifted by 90 ° and are 90 ° symmetrical. Even if the Z-axis is rotated 90 ° about the rotation center, the axial directions of the first wave plate 10 and the second wave plate 20 do not change. By doing in this way, manufacture becomes easy and the polarizing beam conversion element 1 for converting into an eight-fold axisymmetric beam can be produced at low cost. Of course, at least one of the first wave plate 10 and the second wave plate 20 may be rotationally symmetric. Furthermore, since it is a combination wavelength plate element, it can respond to a wide wavelength range. In particular, by preparing a broadband wavelength plate in which quartz and MgF ₂ are combined, components other than the phase plate 30 can be widened.

  A method for manufacturing the phase plate 30 will be described. The phase plate 30 can be created by forming a transparent film on a transparent substrate (glass plate). For example, the thickness of the deposited film is partially changed using a mask. By doing in this way, the phase plate 30 can be produced simply. Alternatively, the phase plate 30 may be created by etching a transparent substrate. In this case, the phase plate 30 can be easily formed by using a resist or the like as a mask. The phase plate 30 may have a configuration other than the above as long as the optical path length varies depending on the incident position. The phase plate 30 needs to be changed according to the wavelength. However, since it is only necessary to prepare transparent transparent plates having different thicknesses, it is possible to cope with a wide wavelength range at a low cost.

In the present embodiment, the second wave plate 20 and the phase plate 30 can be integrally formed. In this case, a transparent film giving a phase difference is formed directly on the λ / 4 plate. For example, a transparent film can be formed on the second wavelength plate by depositing a dielectric film or applying a photocurable resin film. This eliminates the need for a substrate for holding the transparent film, and allows the polarization beam conversion element 1 to be realized at low cost.
Further, the transparent film is preferably formed of a material having a refractive index close to that of the λ / 4 plate. Of course, the same material as the λ / 4 plate can be used as the material having the same refractive index as that of the λ / 4 plate. For example, when the λ / 4 plate is a quartz wavelength plate, SiO ₂ is deposited. When the λ / 4 plate is MgF ₂ , MgF ₂ is deposited. Alternatively, a resist adjusted to the same refractive index as that of SiO ₂ and MgF ₂ and a photocurable resin film are applied.
By doing so, the refractive indexes of the phase plate (transparent film) and the wave plate become close, and loss due to reflection at the interface can be reduced. Therefore, the light use efficiency can be improved. Even when a transparent film is formed of a material having a refractive index different from that of the λ / 4 plate, an appropriate dielectric multilayer film is formed between the λ / 4 plate and the transparent film to reduce loss due to reflection at the interface. it can. However, in this case, the number of manufacturing steps increases as compared with the case where a transparent film having a refractive index close to that of the λ / 4 plate is used. In addition, since the second wavelength plate 20 and the phase plate 20 have the same arrangement of the divided regions, a transparent film having a uniform thickness can be easily formed. That is, before the four pieces of λ / 8 plates or the four pieces of λ / 4 plates are combined, a transparent film having a predetermined thickness may be formed on each piece of the wave plate.

  The case where the left circularly polarized light is changed to radial polarized light will be described with reference to FIGS. FIG. 10 is a diagram showing the axial direction and phase lag when the right circularly polarized light is converted into radial polarized light, and FIG. 11 is a diagram showing the axial direction and phase lag when the left circularly polarized light is converted into radial polarized light. is there.

  As described above, in the case of right circularly polarized light, the axial directions of the regions 51 to 58 are as shown in FIG. Further, the phase difference by the phase plate 30 is as shown in FIG. In the case of left circularly polarized light, the axial orientations of the regions 51 to 58 and the phase difference due to the phase plate 30 are as shown in FIG. In order to obtain such an axial orientation, the first wave plate 10 and the second wave plate 20 are rotated by −90 ° from the state shown in FIGS. 2 and 3. Further, the phase plate 30 is turned over. That is, the phase plate 30 is rotated 180 ° with the −45 ° straight line as the rotation axis. As a result, the positions of the divided area 32 and the divided area 34 are switched. By doing in this way, left circularly polarized light can be made into radial polarized light with the same components as right circularly polarized light. That is, even when the pseudo radial polarization is generated from the right circular polarization and the left circular polarization, the first wave plate 10, the second wave plate 20, and the phase plate 30 can be shared. Further, instead of rotating the first wave plate 10 and the second wave plate 20 by −90 °, even if the first wave plate 10 and the second wave plate 20 are turned over, the same axial orientation is obtained. be able to.

(Generation of pseudo-azimuth polarized light)
Further, an arrangement for generating pseudo azimuth polarized light will be described. When generating pseudo azimuth polarized light from right circularly polarized light, the first wave plate 10 and the second wave plate 20 are turned over. Thereby, the axial direction of the 1st wave plate 10 and the 2nd wave plate 20 will be in the state shown in FIG. The phase plate 30 is arranged as it is, that is, as shown in FIG. With such an arrangement, pseudo-azimuth polarized light can be generated from right circularly polarized light. Instead of turning the first wave plate 10 and the second wave plate 20 upside down, the first wave plate 10 and the second wave plate 20 are rotated by −90 ° from the state shown in FIGS. 2 and 3. You may let them.
When generating pseudo azimuth polarized light from left circularly polarized light, the phase plate 30 is turned over. That is, the phase plate 30 is in the state shown in FIG. At this time, the first wave plate 10 and the second wave plate 20 are in the state shown in FIG. With such an arrangement, the left circularly polarized light can be converted to pseudo azimuth polarized light.
By doing in this way, pseudo radial polarization can be generated with a combination wave plate for generating pseudo radial polarization. That is, the first wave plate 10, the second wave plate 20, and the phase plate 30 can be shared by the pseudo radial polarization and the pseudo azimuth polarization.

Embodiment 2. FIG.
In this embodiment, since the linearly polarized light is pseudo radial polarized light or pseudo azimuth polarized light, the polarization beam conversion element 1 has a configuration shown in FIG. In the present embodiment, a third wave plate 40 is provided in addition to the configuration shown in the first embodiment. Note that description of the structure shown in Embodiment Mode 1 is omitted. The third wave plate 40 is disposed in front of the first wave plate 10. As shown in FIG. 13, the third wave plate 40 is a λ / 4 plate. In FIG. 13, the axis direction of the λ / 4 plate is indicated by a thick line, and the polarization axis of linearly polarized light is indicated by an arrow. The polarization axis of linearly polarized light is inclined 45 ° with respect to the axial direction. Therefore, circularly polarized light is generated when the linearly polarized light passes through the third wave plate 40. Therefore, similarly to Embodiment 1, pseudo radial polarization or pseudo azimuth polarization can be generated.

Embodiment 3 FIG.
In the present embodiment, the polarization beam conversion element 1 for converting the circularly polarized Laguerre Gaussian beam into pseudo radial polarization or pseudo azimuth polarization has the configuration shown in FIG. The Laguerre Gaussian beam has a spiral wavefront. Therefore, adjustment of the phase delay by the first wave plate 10 and the second wave plate 20 becomes unnecessary. The phase plate 30 is removed from the configuration of the first embodiment. Note that description of the structure shown in Embodiment Mode 1 is omitted. In the present embodiment, a Laguerre Gaussian beam in which the wavefront of incident light is spiraled in advance is used, so that it is not necessary to align the phase with the phase plate 30. Of course, the polarization beam converting element 1 according to the present embodiment is not limited to a Laguerre Gaussian beam having a spiral wavefront, but also applied to a pseudo Laguerre Gaussian beam having a spiral stepped wavefront. Is possible. The Laguerre Gaussian beam can be generated using a hologram element or a liquid crystal element.

Embodiment 4 FIG.
In the present embodiment, the polarization beam conversion element 1 for converting the linearly polarized Laguerre Gaussian beam into pseudo radial polarization or pseudo azimuth polarization has the configuration shown in FIG. The Laguerre Gaussian beam has a spiral wavefront. Therefore, adjustment of the phase delay by the first wave plate 10 and the second wave plate 20 becomes unnecessary. The phase plate 30 is removed from the configuration of the second embodiment. That is, the third wavelength plate 40 is added to the configuration of the third embodiment. Note that description of the structure shown in Embodiment Mode 1 is omitted. In the present embodiment, since the wavefront of the incident light is spiraled in advance, it is not necessary to align the phase with the phase plate 30. Of course, the polarization beam converting element 1 according to the present embodiment is not limited to a Laguerre Gaussian beam having a spiral wavefront, but also applied to a pseudo Laguerre Gaussian beam having a spiral stepped wavefront. Is possible. The Laguerre Gaussian beam can be generated using a hologram element or a liquid crystal element.

Other embodiments.
In the above description, the outer shapes of the first wave plate 10, the second wave plate 20, and the phase plate 30 are not limited to squares. For example, the outer shape of the first wave plate 10, the second wave plate 20, and the phase plate 30 may be circular or rectangular. Further, the spot shape of the laser beam is not limited to a circle. For example, a ring-shaped beam can be used. Further, the outline of the wave plate and the phase plate, the angle of the axial direction, and the boundary line of the divided regions may not exactly match the angle values shown. Substantially, it may be arranged so as to obtain pseudo radial polarization or pseudo azimuth polarization. For this reason, the first wave plate 10 has a configuration in which a divided region that is radially divided into four is provided, and a λ / 8 plate is provided in each of the divided regions. In addition, the azimuths of the λ / 8 plates are arranged so as to be substantially orthogonal in the two divided regions adjacent in the circumferential direction and substantially parallel in the two divided regions facing each other. Further, the second wave plate 20 disposed at the subsequent stage of the first wave plate 10 is provided with a divided region that is radially divided into four, and a λ / 4 plate is disposed in each of the divided regions. To do. Then, the azimuths of the λ / 4 plates are arranged so as to be substantially orthogonal to each other in the two divided regions adjacent to each other in the circumferential direction, and to be substantially parallel in the two divided regions facing each other. Further, each of the divided regions of the first wave plate 10 is arranged so as to be shifted from the divided region of the second wave plate 20 so that the axial direction of the λ / 8 plate and the axial direction of the λ / 4 plate are shifted. do it.

  In the first and second embodiments, the phase plate 30 is arranged in the forefront stage, but the arrangement of the phase plate 30 is not particularly limited. That is, since the phase plate 30 does not change the polarization axis, it may be arranged at any location. For example, after the second wave plate 20, between the first wave plate 10 and the second wave plate 20, or between the first wave plate 10 and the third wave plate 40. good.

(Application Example 1: Electron Gun and Electron Generation Method)
The above polarized beam conversion element can be used for an electron gun, a laser processing apparatus, a laser microscope, and the like. For example, by using it for an electron gun, particularly a polarized electron gun, it is possible to achieve high brightness and low emittance of the electron beam. For example, a pseudo radial polarized beam is incident on the photocathode. The electron gun using the pseudo radial polarization beam is described in, for example, Japanese Patent Application Laid-Open No. 2008-288099, Japanese Patent Application Laid-Open No. 2009-031634, Japanese Patent Application Laid-Open No. 2010-015877, and the like. Further, the electron gun includes an electron microscope, an X-ray free electron laser (XFEL), a femtosecond X-ray pulse light source by inverse Compton scattering, a high repetition femtosecond time-resolved electron microscope, an ultrashort pulse electron beam drawing apparatus, an energy recovery device. It is suitable as an electron source such as a mold linac (ERL). Moreover, highly efficient laser processing is realizable by using a polarized beam conversion element for a laser processing apparatus. By using the laser microscope, it is possible to observe with higher accuracy.

  Further, the pseudo radial polarization can be used to generate a Z direction in which an electric vector vibrates in the Z direction. An electron gun that uses Z-polarized light generated by using the polarization beam conversion element and an electron generation method will be described with reference to FIG. FIG. 16 is a diagram showing the configuration of the electron gun.

  The electron gun 100 is a photocathode electron gun that generates electrons when a laser beam 150 is incident on the cathode. The electrons generated by the electron gun 100 are accelerated by the microwave from the microwave source 124. The electron gun 100 according to the present embodiment has a reflective photocathode. That is, the laser beam is irradiated from the electron beam emission side.

  The electron gun 100 includes a laser light source 111, a wavelength conversion element 112, an axicon lens 113, an axicon lens 114, a polarization beam conversion element 115, a mirror 117, a lens 118, a photocathode 121, a resonator 123, and a microwave source 124. is doing.

  The laser light source 111 emits linearly polarized laser light 150. As the laser light source 111, for example, a Ti: Sapphire laser with a regenerative amplifier can be used. Therefore, the laser light source 111 emits pulsed laser light having a wavelength of 790 mm. The light beam from the laser light source 111 becomes a parallel light flux and enters the wavelength conversion element 112. The wavelength conversion element 112 is a nonlinear optical crystal, for example, and converts the wavelength of the laser light 150. Thereby, the wavelength of the laser beam 150 is shortened. As the wavelength conversion element 112, for example, a BBO crystal can be used. That is, the wavelength conversion element 112 generates a second harmonic wave having a wavelength of 395 nm from a fundamental wave having a wavelength of 790 nm. Of course, not only the second harmonic wave but also a third harmonic wave having a wavelength of 263 nm may be used. As described above, the wavelength conversion element 112 converts the wavelength of the laser light 150.

  The wavelength-converted laser beam 150 is incident on a pair of axicon lenses 113 and 114. The axicon lenses 113 and 114 have a conical shape. The laser beam 150 is refracted by a pair of axicon lenses 113 and 114 and converted into a ring-shaped beam. That is, the cross section of the laser beam 150 emitted from the axicon lens 114 has a hollow ring shape. As described above, the pair of axicon lenses 113 and 114 generate an annular beam from the laser light 150. A parallel light beam is emitted from the axicon lens 114. An annular beam may be generated with a configuration other than the pair of axicon lenses 113 and 114. 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. Thus, by providing the annular beam converting means for converting the laser light from the laser light source 111 into an annular light beam, the laser light 150 can be used efficiently.

  Laser light 150 emitted from the axicon lens 114 is incident on the polarization beam conversion element 115. The polarization beam conversion element 115 is the polarization beam conversion element 1 shown in the second embodiment. The polarization beam converting element 115 converts linearly polarized light into radial polarized light whose polarization axis is radial. Precisely, when the linearly polarized laser beam 150 is incident on the polarization beam conversion element 115, a polarization state close to radial polarization is obtained. That is, the linearly polarized light can be changed to pseudo radial polarized light that approximates the radial polarized light. By combining this polarization beam conversion element 115 with the lens 118, it is possible to generate Z polarized light having a large electric field component in the Z direction (optical axis direction). The laser beam 150 converted to Z-polarized light oscillates in the traveling direction of the light.

  The laser beam 150 that has passed through the polarization beam converting element 115 is incident on the mirror 117. The mirror 117 is inclined 45 ° with respect to the optical axis of the laser beam 150. Therefore, the mirror 117 reflects the laser beam 150 toward the photocathode 121. Laser light 150 from the mirror 117 enters the lens 118. In the lens 118, the laser beam 150 is refracted by the lens 118 and enters the photocathode 121. That is, the lens 118 condenses the laser beam 150 and irradiates the photocathode 121.

  The mirror 117 and the lens 118 have a hollow shape with a hollowed central portion. Further, the laser light 150 is formed in a ring shape by the axicon lenses 113 and 114. For this reason, even when the hollow mirror 117 and the lens 118 are used, most of the laser light is incident on the photocathode 121. In other words, the mirror 117 and the lens 118 have a hollow portion corresponding to the annular laser beam 150. Therefore, the annular laser beam 150 does not enter the mirror 117 and the hollow portion of the lens 118. Thereby, most of the laser beam 150 is incident on the photocathode 121. Accordingly, it is possible to prevent a decrease in utilization efficiency of the laser beam 150.

  The laser beam 150 that has passed through the lens 118 enters the opening of the resonator 123. The laser beam 150 passes through the cavity portion of the resonator 123 and enters the photocathode 121. Laser light 150 is focused on the surface of photocathode 121 by lens 118. That is, the surface of the photocathode 121 is disposed at the focal position of the lens 118. Therefore, the condensing point of the laser beam 150 is the surface of the photocathode 121. When the laser beam 150 is incident on the photocathode 121, electrons are generated by the photoelectric effect. Note that the optical axis of the laser beam 150 is perpendicular to the surface of the photocathode 121. That is, the mirror 117 is inclined by 45 ° with respect to the photocathode 121. Therefore, the laser beam 150 is directly incident on the photocathode 121.

  The microwave generated by the microwave source 124 is incident on the resonator 123. The resonator 123 is a cavity resonator, and generates a standing wave corresponding to the input microwave. That is, an electric field for accelerating electrons generated at the photocathode 121 is generated in the resonator 123 that is an RF resonator. Electrons generated at the photocathode 121 are accelerated by an electric field in the resonator 123. That is, the electron beam 160 having a predetermined velocity is emitted from the resonator 123. Here, the timing of the laser light pulse is adjusted in accordance with the standing wave generated in the resonator 123. That is, the microwave from the microwave source 124 and the pulse of the laser beam are synchronized. As a result, electrons are generated from the photocathode 121 at the timing when an accelerating electric field is generated in the resonator 123. Therefore, the electron beam 160 is accelerated efficiently. The accelerated electron beam 160 passes through the mirror 117 and the hollow portion of the lens 118. Thereby, it is possible to prevent a disturbance from occurring in the electron beam 160. That is, the electron beam 160 does not pass through structures such as the mirror 117 and the lens 118. The mirror 117 and the lens 118 do not interfere with the electron beam 160. For this reason, deterioration of the quality of the electron beam 160 can be prevented.

  The electron beam 160 thus obtained passes through a predetermined path, and is an X-ray free electron laser (XFEL), a femtosecond X-ray pulse light source by inverse Compton scattering, a femtosecond time-resolved electron microscope, an ultrashort pulse. It is used for electron beam drawing devices, energy recovery type linacs (ERL), and the like. Note that the mirror 117 and the lens 118 present in the path of the electron beam 160 are disposed in a vacuum. That is, the mirror 117 and the lens 118 are disposed in a vacuum chamber. Accordingly, the laser beam 150 from the polarization beam converting element 115 is incident on the mirror 117 through the window provided in the vacuum chamber. Thus, the polarization beam conversion element 115 is disposed in the atmosphere. Thereby, adjustment of an optical system etc. can be performed easily. For example, the axis orientation of the λ / 4 plate and the λ / 8 plate can be adjusted by rotating the wave plate and the phase plate. Therefore, convenience can be improved.

  Here, by using the polarization beam conversion element 115 and the lens 118, an electric field in the Z direction is generated at the focal position of the laser beam 150. A Schottky effect is generated by applying an electric field in the Z direction to the surface of the photocathode 121. Due to the Schottky effect, the effective work function of the photocathode 121 is reduced, so that the quantum efficiency is increased. Even when laser light having a long wavelength is used, a material that is stable in the atmosphere can be used as the photocathode 121. For example, copper having a work function of about 4 eV or copper diamond having a work function of about 5.5 eV can be used as the photocathode material. In other words, the photocathode 121 can be maintained in the atmosphere. Therefore, maintainability can be improved and the life of the electron gun can be extended. Furthermore, the selection range of the photocathode material can be widened. Further, since laser light having a long wavelength can be used, the laser light source 111 can be prevented from becoming large and complicated. That is, a small laser light source 111 can be used with a simple configuration.

  When a metal material is used for the photocathode 121, the photoelectric effect response is about 10 fsec. Therefore, by irradiating the laser beam 150 in synchronization with the microwave of the microwave source 124, electrons can be accelerated stably.

  In the present embodiment, Z-polarized light is generated using the polarization beam conversion element 115. Electrons are generated using an electric field in the Z direction generated by the laser beam 150. That is, Z-polarized light is incident on the surface of the photocathode 121. Thereby, emittance can be improved as compared with a needled photocathode. Furthermore, since the quantum efficiency can be improved, a high-intensity electron beam 160 can be obtained. Therefore, a high-quality electron beam 160 can be generated with a simple configuration. In addition, the effective work function can be lowered. Therefore, a photocathode material that is stable in the atmosphere, such as metal or diamond, can be used. As a result, it is possible to realize the electron gun 100 with low running cost and high maintainability.

(Application example 2: Beam measuring device)
Furthermore, the polarization beam conversion element described above can also be used for the beam measuring apparatus and the beam measuring method disclosed in Japanese Patent Application Laid-Open No. 2008-288087. Pseudo radial polarization is generated using the polarization beam conversion element of the present embodiment. Further, an electro-optic element having a hollow portion through which the beam passes is disposed in the path of the electron beam to be measured. When the electron beam bunch passes through the hollow portion of the electro-optic element, the crystal axis of the electro-optic element changes. Further, in synchronization with the electron beam, the hollow pseudo radial polarized light is passed through the electro-optic element in the path. Then, the polarization state of the pseudo radial polarization changes according to the axial direction of the crystal axis. Therefore, the three-dimensional spatial distribution of the beam can be measured by examining the polarization state of the light that has passed through the electro-optic element.

  The configuration of the beam measuring apparatus will be described with reference to FIG. FIG. 17 is a diagram showing the configuration of the beam measuring apparatus 200, which basically has the same configuration as that described in Japanese Patent Application Laid-Open No. 2008-288087. Since the basic concept of the beam measuring apparatus 200 is disclosed in Japanese Patent Application Laid-Open No. 2008-288087, detailed description thereof is omitted.

  The laser light source 201 emits laser light serving as probe light. Laser light emitted from the laser light source 201 is linearly chirped by the optical modulator 202 and the photonic crystal 203. Therefore, the laser light emitted from the photonic crystal 203 has a linear relationship between wavelength and time. The optical modulator 202 is, for example, DAZZLER (registered trademark) UWB-650-1100 manufactured by FASTLITE, and modulates the time waveform of the pulse laser beam. The photonic crystal broadens the bandwidth of laser light by a non-linear optical effect. The pulse waveform of the pulse laser beam is shaped and emitted so that the wavelength of the pulse laser beam oscillated by the laser oscillator changes with time.

  The linearly chirped light beam enters the polarization beam conversion element 204. The polarized beam 05204 converts the light beam into radial polarization as described above. The light beam which has been converted into pseudo-radial polarized light by the polarization beam conversion element 204 is incident on a pair of axicon lenses 205 and 206. The pair of axicon lenses 205 and 206 makes the light beam spot hollow and generates an annular beam. The annular radial polarized beams from the axicon lenses 205 and 206 are incident on the timing control plate 207. The timing control plate 207 gives a delay time for each divided region. That is, the timing control plate 207 is different in thickness, material, and the like so that the optical path length changes every eight divided regions. The timing control board 207 gives a delay time of 10 psec or more to each divided region, for example. A predetermined delay time is given to each of the polarization directions of the eight-divided pseudo radial polarized light beam.

  The light beam from the timing control plate 207 enters the mirror 208. The mirror 208 is disposed in the beam path of the electron beam 220. The mirror 208 is inclined 45 ° with respect to the optical axis of the laser beam. Therefore, the mirror 208 reflects the laser light in the direction of the mirror 211. The laser beam from the mirror 208 propagates in the traveling direction of the electron beam. That is, the pulse laser beam propagates downstream of the electron beam. The mirror 211 is also hollow like the mirror 208 and is disposed in the path of the electron beam 220. Laser light is extracted from the path of the electron beam 220 by the mirror 211.

  The mirrors 208 and 211 have a hollow shape with a central portion cut out. Further, the axicon lenses 205 and 206 form a laser beam in a ring shape. For this reason, even when the hollow mirrors 208 and 211 are used, most of the laser light is reflected by the mirrors 208 and 211. 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.

  An electro-optic crystal 209 or a car material 210 is disposed between the mirror 208 and the mirror 211. The electro-optic crystal 209 is a crystal exhibiting an electro-optic effect, and the crystal axes are radially arranged. In the electro-optic crystal 209, the refractive index changes due to the electric field generated by the electron beam 220. As the electro-optic crystal 209, a Pockels element whose refractive index changes in proportion to the strength of the electric field can be used. The car material 210 is a material that exhibits a Kerr effect, and for example, an amorphous material can be used. In the Kerr material 210, the refractive index changes due to the electric field generated by the electron beam 220. In the Kerr effect, the refractive index changes in proportion to the square of the electric field strength. The electro-optic crystal 209 or the car material 210 is hollow like the mirrors 208 and 211, and the electron beam 220 passes through the hollow portion. Thereby, nondestructive beam measurement is possible. In the following description, an example in which the electro-optic crystal 209 is disposed in the beam path will be described.

  When the bunch of the electron beam 220 passes through the hollow portion of the electro-optic crystal 209, the timing is adjusted so that the laser light passes through the electro-optic crystal 209. By doing so, the laser light is affected by the refractive index change of the electro-optic crystal 209. For example, when an electric field parallel to the crystal axis is applied, the refractive index in the crystal axis direction changes. At this time, in the plane perpendicular to the optical axis of the laser light, the refractive index does not substantially change in the direction perpendicular to the crystal axis. Therefore, in the electro-optic crystal 209, the refractive index changes in proportion to the electric field strength, and birefringence is induced. By birefringence, linearly polarized light is converted into elliptically polarized light in each divided region. The inclination of elliptically polarized light changes according to the electric field strength. Further, the electric field strength in the electro-optic crystal 209 reflects the spatial distribution of the electron beam 220. When the radial polarization beam is incident on the electro-optic crystal 209, the polarization state is changed according to the spatial distribution of the electron beam 220 that is simultaneously incident on the electro-optic crystal 209. The electro-optic crystal 209 is divided into eight parts similarly to the timing control plate 207, and the crystal axes are radial, for example.

  The light beam whose polarization state has been changed by the electro-optic crystal 209 enters the mirror 211. A light beam is extracted from the path of the electron beam by the mirror 211. The light beam is incident on the wave plate 212. The light beam that has passed through the wave plate 212 is incident on the polarization beam splitter 213. The retardation generated by the electro-optic crystal 209 is separated into orthogonal polarization components by the polarization beam splitter 213. As described above, the polarization beam splitter 213 extracts a predetermined polarization component from the pulsed laser light incident from the incident optical system via the electro-optic crystal 209. Then, the spectroscopes 214 and 215 perform spectroscopic measurement for each orthogonal component. Thereby, a spectrum is measured for each of the orthogonal components.

  Here, the laser light incident on the electro-optic crystal 209 is chirped. Further, a delay time is given to the laser light incident on the electro-optic crystal 209 by the timing control plate 207. Therefore, the wavelength of the laser beam affected by the retardation by the electro-optic crystal 209 differs in the divided regions. That is, in the traveling direction of the light beam, the wavelength of the laser beam at the same position as the bunch of the electron beam 220 differs in the divided regions. Therefore, by performing spectroscopic measurement, the light intensity of each divided region can be measured independently. Furthermore, the spatial distribution of the electron beam can be measured by performing spectrum measurement on each of the orthogonal components.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, the central angle of the divided region of each phase difference plate is not strictly limited to 90 °. That is, by dividing into four parts, the central angle becomes close to a right angle, so that the central angle can be made larger than in the case of dividing into eight parts. By doing so, the wave plate can be cut out easily.

(Extension of polarization beam conversion element to ²ⁿ division)
In the above description, two divided 4-wave plates are combined to generate 8-divided pseudo radial polarized light. However, the polarization beam converting element according to the present invention combines two 2 ^n- divided wave plates into 2 It can be extended to a configuration for conversion to ^{(n + 1)} -division pseudo-radial polarization (where n is a natural number of 2 or more). The case of extending to n division will be described.

In order to satisfy the rotational symmetry, the incident light is circularly polarized. Either right or left circularly polarized light may be used, but in the following description, a case where clockwise circularly polarized light is incident is considered. The polarization state is considered with the Poincare sphere shown in FIG. Consider the polarization state on the Poincare sphere. It is assumed that the diameter of the sphere is normalized to 1. The Poincare sphere coordinates are expressed in polar coordinates (ψ, χ).
However,
S ₁ = cosχcosψ
S ₂ = cosχsinψ
S ₃ = sinχ
S ₁ ² + S ₂ ² + S ₃ ² = 1
It is.

The first wave plate 10 and the second wave plate 20 are divided into ^2n, and the divided region having the smallest angle with the X axis is defined as the first divided region. For clarity of explanation, the wavelength plate in the first divided region of the first wave plate 10 is referred to as a wave plate 1-1, and the wave plate in the first divided region of the second wave plate 20 is referred to as a wave plate 2-1. To do. Further, the first wave plate 10 is assumed to be a wave plate 1-2, a wave plate 1-3,..., A wave plate 1-n counterclockwise from the wave plate 1-1. Similarly, the second wave plate 20 is also referred to as a wave plate 2-2, a wave plate 2-3,..., A wave plate 2-n counterclockwise from the wave plate 2-1. Central angle of the waveplate 1-1 to 1-8, and the wavelength plate 2-1 to 2-8 becomes 2π / ^{2 n.} In the example in which two 2 ³ = 8 divided wave plates are combined to generate 2 ⁴ = 16 divided pseudo-radial polarized light, the first wave plate 10 and the second wave plate 20 are shown in FIGS. As shown. FIG. 19 is a front view showing the first wave plate 10 divided into eight, and FIG. 20 is a front view showing the second wave plate 20 divided into eight.

FIG. 21 is a projection view of the Poincare sphere viewed from the north pole side. The clockwise circularly polarized light of the incident light is the north pole (ψ, χ) = (0, π / 2) on the Poincare sphere (point A). Incident light passes through the wave plate 1-1 and changes to a polarization state represented by point B on the Poincare sphere. In order to generate 2 ^{n + 1} divided radial polarized light, the angle between the polarization direction of the light transmitted through the wave plate 1-1 and the wave plate 2-1 and the x axis may be π / 2 ^{n + 1} . This polarization state is represented by (ψ, χ) = (π / 2 ⁿ , 0) on the Poincare sphere (point C). Angle between the polarization direction and the x-axis of the light passing through the wavelength plate 1-1 and the wavelength plate 2-2 ⁿ may if the π / 2 n ^{+ 1.} This polarization state is represented by (ψ, χ) = (− π / 2 ⁿ , 0) on the Poincare sphere (point D).

Consider the condition to be satisfied by point B.
Since the wavelength plate 2-1 and the wavelength plate 2-2 ⁿ is the wavelength plate of the same phase difference, the distance along the surface of the sphere between B and C, and along the surface of the sphere between the B and D The distance is required to be equal. Therefore, the point B needs to be a point on the S ₁ S ₃ plane (on the S ₁ axis in the projection from the North Pole).
The difference from the rotational symmetry, the angle and the wavelength plate 2-1 x-axis, wave plates 2-2 ⁿ is the x-axis and the angle is 2π / ^{2 n.} In order to shift the polarization state from B to C and from B to D by the wave plate having such an angle difference, it is necessary that CBD = 2π / 2 ⁿ⁻¹ on the projection from the north pole. is there. From the above conditions, the position of the point B is obtained as (0, arccos (0.5 / cos (π / 2 ⁿ )).

The position of the point B is derived as follows with reference to FIG.
2. From ∠CAB = ∠CBE, AB = BC (isosceles triangle)
From AC = 1, AB = 0.5 / cos (∠CAB) = 0.5 / cos (π / 2 ⁿ )
χ = arccos (AB) = arccos (0.5 / cos (π / 2 ⁿ )

Since the wave plate 1-1 changes the polarization state from the point A to the point B, the following may be used.
Angle between axis direction and x axis: -π / 4
Phase difference: (λ / 4) × (1-arccos (0.5 / cos (π / 2 ⁿ )) / (π / 2)) (2)

Since the wave plate 2-1 changes the polarization state from the point B to the point C, the following may be used.
Angle between axis direction and x axis: π / 2 ⁿ −π / 4
Phase difference: (λ / 4) × (arccos (1-0.5 / cos ² (π / 2 ⁿ )) / (π / 2)) (3)

From the rotational symmetry, the axial directions of the remaining wave plates can be easily obtained. In other words, the difference between the axial direction of the wave plate of the divided regions adjacent may if the 2π / 2 ^n. Thereby, the axial directions of the wave plates of the two divided regions facing each other become parallel. The wave plates 1-1 to 1-n provided on the first wave plate 10 all have the same phase difference, and all the wave plates 2-1 to 20n provided on the second wave plate 20 are also included. The same phase difference. The axial orientation of the wave plate provided on the first wave plate 10 and the axial orientation of the wave plate provided on the second wave plate 20 are shifted by π / ²ⁿ . That is, in the divided region of the second wave plate 20 overlapping divided area and a portion of the first wave plate 10, the angle formed by the axial orientation of the overlapping divided area becomes 2 [pi / 2 ^n. Further, the divided region of the first wave plate 10 and the divided region of the second wave plate 20 are shifted on the XY plane. In the XY plane, the divided region of the first wave plate 10 and the divided region of the second wave plate 20 are shifted by π / 2 ⁿ . Accordingly, if one of the divided regions of the first wave plate 10 is divided into two equal parts along the x axis, one of the boundary lines of the divided regions of the second wave plate 20 coincides with the x axis.

  When the phase of the light transmitted through the first wave plate 10 and the second wave plate 20 is obtained, the phase of the light transmitted through the wave plate 1-1 and the wave plate 2-1, and the wave plate 1- 2 and the light transmitted through the wave plate 2-1 are in phase. It can be seen from the rotational symmetry that the phase of the light transmitted through the wave plate 1-2 and the wave plate 2-2 and the phase of the light transmitted through the wave plate 1-3 and the wave plate 2-2 are also aligned. That is, the phases of the light transmitted through one divided region in the second wave plate 20 are aligned.

When the phase of the light wave plate 2-2 having transmitted through the wavelength plate 2-1 compares the phase of light transmitted, the phase of light transmitted through the wavelength plate 2-2, 2 [pi / 2 ⁿ by a phase is delayed . In adjacent divided regions of the second wave plate 20, the phase is delayed by 2π / 2 ^{n when the} boundary is exceeded counterclockwise as viewed from the incident side. This phase difference can be corrected by using a phase plate divided in the same manner as the second wave plate 20. Specifically, a divided phase plate having a phase difference increased by 2π / 2 ⁿ (λ / 2 ⁿ ) clockwise as viewed from the incident side is used. By this divided phase plate, an optical path length difference of 2π / 2 ⁿ (λ / 2 ⁿ ) is given to light passing through adjacent divided regions. This retardation may be given by a retardation film formed on the second wave plate by vapor deposition or the like. That is, the phase plate 30 may be formed directly on the second wave plate 20.

When counterclockwise circularly polarized light is incident, a set of wave plates obtained by rotating the axis orientation of each wave plate by π / 2 is used, and 2π / 2 ⁿ (λ / 2 ⁿ ) is rotated counterclockwise. Radial polarized light can be generated by using a divided phase plate in which the phase difference is changed. This is the same as turning over each of the first wave plate 10, the second wave plate 20, and the phase plate 30. Even when the retardation film is directly formed on the second wave plate, it can be used as it is. The first wave plate 10 and the second wave plate 20 can be separated so that each can be turned over, and can be assembled even when turned over.

  In the case of generating azimuth polarized light, the method described in (Generation of pseudo azimuth polarized light) can be used. For example, the counterclockwise circularly polarized light is preferably incident on a combination for generating radial polarized light from the clockwise circularly polarized light (or vice versa). At this time, the phase plate 30 is turned upside down. In this way, azimuth polarized light can be generated.

Thus, in each divided region of the first wave plate 10, the phase difference indicated by the equation (2) is given to the orthogonal component, and in each divided region of the second wave plate 20, the orthogonal component is expressed by the equation. The phase difference indicated by (3) is given. In the first wave plate 10, the axis orientation of the adjacent divided regions, arranged such that different 2π / 2 ^n. Similarly, in the second wave plate 20, the axial orientation of the adjacent divided regions, arranged such that different 2 [pi / 2 ^n. Furthermore, the central angle of each divided region is 2π / 2 ^n. By doing so, the first wave plate 10 and the second wave plate 20 are rotationally symmetric. Further, in the case of a non-Laguerre Gaussian beam, a phase plate having ²ⁿ divided regions arranged to coincide with the divided regions of the second wave plate 20 in a plane perpendicular to the optical axis is further provided. Then, the phase plate 30 gives an optical path length difference corresponding to λ / 2 ⁿ in the adjacent divided regions. The wavelength plate of the first wave plate 10 and the wave plate of the second wave plate 20 are arranged so that the axis direction of the wave plate is shifted by approximately π / 2 ⁿ . By doing so, it can be approximated to pseudo radial polarization or pseudo azimuth polarization.

(When n = 1)
Next, the case where n = 1 will be described with reference to FIGS. When n = 1, two two-divided wave plates are prepared to generate four-divided pseudo radial polarized light or pseudo azimuth polarized light. FIG. 23 is a front view of the first wave plate 10, FIG. 24 is a front view of the second wave plate 20, and FIG. 25 is a front view of the phase plate 30. FIG. 23 to FIG. 25 each show a configuration viewed from the beam incident side. When n = 1, the incident light is 45 ° linearly polarized light. That is, linearly polarized light having a polarization plane inclined + 45 ° from the x-axis is incident on the first wave plate 10. By arranging a λ / 2 plate or a λ / 4 plate in front of the first wave plate 10, incident light can be converted into 45 ° linearly polarized light. When n = 1, it becomes a singular point that does not apply to the above equations (2) and (3). In the following description, an example in which 45 ° linearly polarized light is converted into four-division pseudo radial polarized light will be described.

  The first wave plate 10 is radially divided into two as in the case where n is 2 or more. In the present embodiment, as shown in FIG. 23, the first wave plate 10 has divided regions that are divided into left and right halves. That is, the boundary line between the first divided area and the second divided area is in the y direction. In the wave plate 1-1 in the right divided region, the axial direction is the x direction, and in the wave plate 1-2 in the left divided region, the axial direction is the y direction. Thus, the axial direction of the wave plate 1-1 and the axial direction of the wave plate 1-2 are orthogonal.

  The second wave plate 20 is radially divided into two as in the case where n is 2 or more. In the present embodiment, the second wave plate 20 has a divided region that is divided into two equal parts. That is, the boundary line between the first divided region and the second divided region is in the x direction. In the wave plate 2-1 in the upper divided region, the axial direction is the x direction, and in the wave plate 2-2 in the lower divided region, the axial direction is the y direction. Thus, the axial direction of the wave plate 2-1 and the axial direction of the wave plate 2-2 are orthogonal. By doing in this way, it can convert into the radial polarization state of 4 divisions. Moreover, since it is only necessary to prepare two two-divided wave plates, the cost can be reduced.

  Further, in the case of a non-Laguerre Gaussian beam, the phase plate 30 shown in FIG. 25 is arranged at the subsequent stage of the second wave plate 20. Of course, the phase plate 30 may be formed directly on the second wave plate 20 as described above. The phase plate 30 has four divided areas. When the phase of the first quadrant is the reference (0), the second quadrant is λ / 4 (π / 2), the third quadrant is λ / 2 (π), and the fourth quadrant is 3λ / 4 (3π / 2). ) Only delay the phase. Thus, the phase can be made uniform by arranging the four-divided phase plate 30 and delaying the phase.

  In order to generate four-division azimuth polarized light, −45 ° linearly polarized light may be incident on the first wave plate 10. Alternatively, the first wave plate 10, the second wave plate 20, and the phase plate 30 may be inverted to generate four-division pseudo azimuth polarized light. (Please check if it is correct)

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, the phase difference, axial orientation, and the like given in the divided regions of each wave plate do not have to exactly match the above formulas and values.

DESCRIPTION OF SYMBOLS 1 Polarization beam conversion element 10 1st wavelength plate, 11 1st division area, 12 2nd division area,
13 3rd division area, 14 4th division area 20 2nd wavelength plate, 21 1st division area, 22 2nd division area 23 3rd division area, 24 4th division area,
30 phase plates, 31 first divided area, 32 second divided area,
33 Third divided region, 34 Fourth divided region 100 Electron gun 100, 111 Laser light source, 112 Wavelength conversion element 112
113 axicon lenses, 114 axicon lenses, 115 polarization beam conversion elements,
117 mirror, 118 lens, 121 photocathode, 123 resonator,
124 Microwave source, 150 Laser light 201 Laser light source 202 Optical modulator 203 Photonic crystal 204 Polarizing beam conversion element 205 Axicon lens 206 Axicon lens 207 Timing control plate 207
220 Electron beam 211 Hollow mirror 212 Wave plate 213 Beam splitter

Claims (18)

A polarization beam conversion element that includes first and second wave plates, and generates pseudo radial polarization or pseudo azimuth polarization,
The first wave plate is provided with divided regions that are radially divided by 2 ⁿ (n is a natural number of 2 or more), and (λ / 4) × (1-arccos (0.5 / Cos (π / 2 ⁿ )) / (π / 2)) is provided.
The axial direction of the divided wave plate of the first wave plate is substantially rotationally symmetric,
The second wave plate disposed at the subsequent stage of the first wave plate is provided with a divided region divided into ²ⁿ radially, and each of the divided regions has (λ / 4) × (arccos (1 A divided wave plate that provides a phase difference of −0.5 / cos ² (π / 2 ⁿ )) / (π / 2));
The axial direction of the divided wave plate of the second wave plate is substantially rotationally symmetric,
Each of the divided regions of the first wave plate is arranged to be shifted from the divided region of the second wave plate,
A polarization beam conversion element in which an axial direction of a divided wave plate provided on the first wave plate is shifted from an axial direction of the divided wave plate of the second wave plate. The first wave plate, and a polarization beam conversion device according to claim 1, wherein at least one of the second wave plate is characterized that it is rotationally symmetrical of 2 [pi / 2 ^n. A phase plate having ²ⁿ divided regions arranged to coincide with the divided regions of the second wave plate in a plane perpendicular to the optical axis;
3. The polarization beam converting element according to claim 1, wherein the phase plate gives an optical path length difference corresponding to λ / 2 ⁿ in divided regions adjacent to each other. 4. The axial direction of the division | segmentation wavelength plate of a said 1st wavelength plate and the axial direction of the said division | segmentation wavelength plate of a said 2nd wavelength plate have shifted | deviated substantially (pi) / ^2n. Polarized beam conversion element. The boundary line of the said division area of the said 1st wavelength plate and the boundary line of the said division area of the said 2nd wavelength plate have shifted | deviated substantially (pi) / ²ⁿ . Polarized beam conversion element. n = 2,
6. The polarization beam converting element according to claim 1, wherein each of the four divided regions of the first wave plate and the four divided regions of the second wave plate has a rectangular shape. A third wave plate disposed in front of the first wave plate;
The polarization beam converting element according to any one of claims 1 to 6, wherein the linearly polarized light incident on the third wave plate is circularly polarized light. A polarization beam conversion element that includes first and second wave plates, and generates pseudo radial polarization or pseudo azimuth polarization,
The first wave plate is provided with a divided region that is radially divided into two, and a λ / 4 plate is provided in each of the divided regions,
The axial direction of the λ / 4 plate of the first wave plate is substantially orthogonal,
The second wave plate provided at the subsequent stage of the first wave plate is provided with divided regions that are radially divided into two, and each of the divided regions is provided with a λ / 4 plate,
The axial direction of the λ / 4 plate of the first wave plate is substantially orthogonal,
Each of the divided regions of the first wave plate is a polarization beam converting element arranged so as to be shifted from the divided region of the second wave plate. In a plane perpendicular to the optical axis, four divided regions divided by two boundary lines that coincide with the boundary line of the divided region of the first wave plate and the boundary line of the divided region of the first wave plate A phase plate having
The polarization beam converting element according to claim 8, wherein an optical path length difference corresponding to λ / 4 is provided in a divided region where the phase plate is adjacent.   The polarization beam conversion element according to claim 3 or 9, wherein the phase plate and the second wave plate are integrally formed. The phase plate is constituted by a deposited film deposited on the second wave plate,
The polarization beam converting element according to claim 10, wherein the phase plate is formed by vapor-depositing the same material as that of the second wave plate.   The axial direction of the λ / 4 plate of the first wave plate and the axial direction of the λ / 4 of the second wave plate are parallel to each other. Polarized beam conversion element.   The polarization according to any one of claims 8 to 12, wherein a boundary line of the divided region of the first wave plate and a boundary line of the divided region of the second wave plate are shifted by approximately π / 2. Beam conversion element. A polarization beam conversion method for generating pseudo radial polarization or pseudo azimuth polarization,
Making circularly polarized light incident on the first wave plate;
Allowing the light that has passed through the first wave plate to enter the second wave plate,
The first wave plate is provided with divided regions that are radially divided by 2 ⁿ (n is a natural number of 2 or more), and (λ / 4) × (1-arccos (0.5 / Cos (π / 2 ⁿ )) / (π / 2)) is provided.
The axial direction of the divided wave plate of the first wave plate is rotationally symmetric,
The second wave plate disposed at the subsequent stage of the first wave plate is provided with a divided region divided into ²ⁿ radially, and each of the divided regions has (λ / 4) × (arccos (1 A divided wave plate that provides a phase difference of −0.5 / cos ² (π / 2 ⁿ )) / (π / 2));
The axial direction of the divided wave plate of the second wave plate is rotationally symmetric,
Each of the divided regions of the first wave plate is arranged to be shifted from the divided region of the second wave plate,
A polarization beam conversion method, wherein an axial direction of a divided wave plate provided on the first wave plate is shifted from an axial direction of the divided wave plate of the second wave plate. A polarization beam conversion method for generating pseudo radial polarization or pseudo azimuth polarization,
Making circularly polarized light incident on the first wave plate;
Allowing the light that has passed through the first wave plate to enter the second wave plate,
The first wave plate is provided with a divided region that is radially divided into two, and a λ / 4 plate is provided in each of the divided regions,
The axial direction of the divided wave plate of the first wave plate is substantially rotationally symmetric,
The second wave plate provided at the subsequent stage of the first wave plate is provided with divided regions that are radially divided into two, and each of the divided regions is provided with a λ / 4 plate,
The axial direction of the divided wave plate of the first wave plate is substantially rotationally symmetric,
The polarization beam conversion method, wherein each of the divided regions of the first wave plate is shifted from the divided region of the second wave plate. The polarization beam conversion element according to any one of claims 1 to 13,
A lens that collects the pseudo-radial polarized light generated by the polarization beam converting element;
An electron gun comprising: a photocathode on which light collected by the lens is incident. A step of causing circularly polarized light to enter the polarizing beam converting element according to any one of claims 1 to 13,
Condensing the pseudo-radial polarized light generated by the polarization beam converting element and making it incident on a photocathode. 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;
Incident having a 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, and a polarization beam converting element that converts the pulsed laser light into a different polarization state according to the incident position Optical system,
An electro-optic element disposed in a beam path of the quantum beam and having a refractive index changed by the electric field;
A polarizer for extracting a predetermined polarization component from pulsed laser light incident from the incident optical system via the electro-optic element;
A measuring instrument for measuring the spectrum of the pulsed laser light extracted by the polarizer,
A beam measuring apparatus using the polarization beam conversion element according to claim 1 as the polarization beam conversion element.

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