JP2007249059A - Light intensity distribution shaping device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light intensity distribution shaping device easily, with good reproducibility, and inexpensively, which performs spatial and temporal shaping of a light intensity distribution, and which is less restrained from limiting optical wavelengths for shaping compared with a conventional method. <P>SOLUTION: The light intensity distribution shaping device 1 which shapes and emits incident light 2 includes a bundle of fibers 10, and optical path lengths up to an exit plane 8 from an incident plane 6 of the optical intensity distribution shaping device 1 of the incident light 2 branched by each optical fiber 10a to 10g composing the bundle of fibers 10 are distributed in a predetermined mode corresponding to the positions in the cross sectional positions of the bundle of the optical fibers 10a to 10g each through which the branched incident light 2 propagates. Since the incident light 2 overlap each other spreading radially after branched, the spatial non-uniformity is eased, and since they overlap each other with time differences, the temporal non-uniformity is eased. The limit of optical wavelengths for shaping depends only on transmittance of the optical fibers in a target wavelength range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light intensity distribution shaping device such as a pulsed laser beam.

  In order to realize a high-performance accelerator, an apparatus capable of generating a low emittance electron beam is required as an electron source for the accelerator. When an electron beam is generated by irradiating a photocathode with a pulse laser beam, it is important for realizing a low emittance to make the three-dimensional pulse shape of the pulse laser beam spatially and temporally uniform.

  In general, a high-intensity pulsed laser light source used for such a purpose has a non-uniform spatial and temporal light intensity distribution. In order to remove the non-uniformity, there is a method of cooling the crystal of the laser light source to the temperature of liquid nitrogen, but there is a problem that the laser device is enlarged. Therefore, a light intensity distribution shaping device that shapes the emitted laser light has been studied.

  Patent Document 1 discloses a method of spatially uniformizing the intensity distribution of laser light using a bundle fiber and a digital micromirror device. In this case, the laser light is not directly incident on the bundle fiber, but the beam is distributed to each fiber using a digital micromirror device to reduce the energy loss of the laser light, and the laser light intensity distribution is spatially changed. It is uniform.

Non-Patent Document 1 discloses a method of temporally shaping a pulse laser beam intensity distribution using a diffraction grating and a liquid crystal spatial light modulator (LC-SLM). Here, by shaping the temporal intensity distribution of the laser light from a Gaussian shape to a rectangle, the space charge effect when incident on the photocathode is suppressed and a low emittance electron beam is generated.
JP 2004-251979 A J. Yang et.al., J. Appl. Phys. Vol. 92 No. 3, p. 1608-1612 Aug. 2002

  However, the method of shaping the intensity distribution of the laser beam disclosed in the above two documents spatially or temporally uses a digital micromirror device and an LC-SLM, respectively. Therefore, there is a problem that the apparatus is expensive, and an optical system that requires complicated fine tuning and a special optimization algorithm for its control is necessary. In general, it is difficult to measure the temporal laser light intensity distribution (pulse waveform), and there is only a streak camera especially in the most necessary ultraviolet region. It is not practical to always use such a very expensive device as a part of a simple laser pulse waveform optimization system.

  In addition, these methods also have a problem that it is not possible to simultaneously perform spatial and temporal shaping of the light intensity distribution with a single device. There is also a method of using each shaping device together, but since it may interfere with each other, it is necessary to control while monitoring the laser wavefront shape and spectral phase distribution, and it becomes a very complicated control system There is. Furthermore, in the control of temporal light intensity distribution using LC-SLM, laser light with a wavelength of 400 nm or less cannot be shaped due to problems with liquid crystal materials, and in the ultraviolet laser light, diffraction efficiency in that wavelength region is not possible. However, since there is no diffraction grating having a high wavelength dependency and a small wavelength dependency, there is a problem that the energy loss of laser light is large when shaping.

  The present invention has been made to solve such a conventional problem, and performs spatial and temporal shaping of the light intensity distribution at the same time, and limits the wavelength of the light to be shaped as compared with the conventional method. An object of the present invention is to provide a less number of light intensity distribution shaping devices at a low cost with a simple device configuration.

  The light intensity distribution shaping device according to the present invention is a light intensity distribution shaping device that shapes and emits incident light. The light intensity distribution shaping device includes a bundle fiber, and is incident on each of the optical fibers constituting the bundle fiber. The optical path length from the entrance surface to the exit surface of the light intensity distribution shaping device is a spatio-temporal in a predetermined manner corresponding to the position in the bundle fiber cross section of each optical fiber through which the branched incident light propagates. It is distributed in the upper region.

  In this light intensity distribution shaping device, incident light is incident on a bundle fiber to be branched into a large number of branched lights. Each of the branched lights propagates radially by diffraction when propagating from the exit end face of each optical fiber constituting the bundle fiber. As a result, most of the branched outgoing lights overlap each other, and spatial nonuniformity is alleviated. Further, in this light intensity distribution shaping device, the optical path length of each branched incident light is not constant, and corresponds to the position in the cross section of the bundle fiber of each optical fiber through which each branched incident light has propagated. Since the light is distributed in a predetermined manner, the time taken for each branched incident light to reach the output side end face of each optical fiber is different. As a result, each branched outgoing light having a time difference overlaps, and the nonuniformity of the time intensity distribution is alleviated.

  Moreover, it is preferable that the length of each optical fiber is changed corresponding to the position in the cross section of the bundle fiber, thereby giving a predetermined distribution. In this case, since the length of propagation of each branched incident light in each optical fiber is different, distribution can be given to the optical path length of each branched light, and the optical path length can be greatly changed. As a result, it is possible to deal with various types of incident light, and it is possible to shape the light intensity distributions of various modes temporally and spatially.

  Further, the relative refractive index difference of each optical fiber is changed corresponding to the position in the cross-section of the bundle fiber, and it is preferable that the distribution is given to the region on the spatiotemporal space of a predetermined mode. . In this case, the refractive index of the core layer through which each branched incident light propagates, the distance that each branched incident light oozes out to the cladding layer, and the total reflection angle are different, so the incident angle of the incident light is different. Depending on the reason, it is possible to give a distribution to the optical path length of each branched incident light because there is an optical fiber that propagates and an optical fiber that does not propagate. As a result, the light intensity distribution shaping device can be manufactured by a simple method in which a bundle fiber is constituted by a plurality of types of optical fibers having different relative refractive index differences.

The light intensity distribution shaping device further includes one or a plurality of optical elements, and the optical elements are incident on the side opposite to the incident light traveling direction from the incident side end face of the bundle fiber, or on the output side end face of the bundle fiber. Arranged on at least one side of the light traveling direction side,
The optical thickness in the optical axis direction of the portion corresponding to each optical fiber of the optical element is changed corresponding to the position in the cross-section of the bundle fiber of each optical fiber, whereby the distribution of the predetermined mode is changed. Preferably it is given. In this case, it is possible to give a distribution to the optical path length of the incident light branched by the optical element. As a result, various modes of incident light can be dealt with by a simple method of exchanging only the optical element, and the light intensity distributions of various modes can be shaped temporally and spatially.

  Moreover, it is preferable to provide a light intensity distribution shaping device and a photocathode provided in the traveling direction of the emitted light of the light intensity distribution shaping device. In this case, laser light shaped into an appropriate light intensity distribution can be incident on the photocathode. As a result, an apparatus for generating a low emittance electron beam can be realized.

  According to the present invention, the spatial and temporal shaping of the light intensity distribution is performed at the same time, and the light wavelength distribution shaping apparatus is less expensive and simpler and more reproducible than the conventional method. Provided to.

  Embodiments of a light intensity distribution shaping device according to the present invention will be described below in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected about the same or equivalent element, and the description is abbreviate | omitted when description overlaps.

  FIG. 1 is a schematic cross-sectional view of a light intensity distribution shaping device according to the present invention. As shown in FIG. 1, the housing 3 of the light intensity distribution shaping device 1 is provided with an entrance surface 6 and an exit surface 8, and a bundle fiber 10 is disposed at a position between them. The incident surface 6 and the exit surface 8 are holes provided in the housing 3, or a material such as glass that is transparent to the light to be shaped, or the incident surface 6 transmits the incident light 2 to the incident side end surface 12. A lens that focuses light to match the NA of the optical fiber, a lens that enlarges the incident diameter to be allocated to a sufficient number of optical fibers, or a light-emitting photocathode that emits the beam diameter of the outgoing light 4 You may comprise with the lens for adjusting to the diameter of this. Moreover, the bundle fiber 10 is comprised by each optical fiber 10a-10g. In FIG. 1, it is composed of seven optical fibers, but is usually composed of a larger number of optical fibers. The lengths of the optical fibers 10a to 10g are distributed in a predetermined manner. Specifically, for example, the lengths of the optical fibers 10 a to 10 g are different within a range of 5%, and the shortest optical fiber is disposed at the center position of the bundle fiber 10. The length of the optical fiber is proportional to the Nth power of the distance from the optical fiber at the center position (N is an integer of 1 or more), or is an exponential function of the distance. Distributed. Alternatively, the longest optical fiber is arranged at the center position of the bundle fiber 10, and the length of each optical fiber is inversely proportional to the Nth power of the distance from the optical fiber at the center position (N is an integer of 1 or more) as described above. Or may be distributed so as to be an exponential function of the distance. The incident light 2 incident from the incident surface 6 is incident on the incident side end surface 12 of the bundle fiber 10, and then is branched by the optical fibers 10 a to 10 g constituting the bundle fiber 10. Propagates within 10 g. Thereafter, the light is emitted from the emission-side end surface 14 and further emitted from the emission surface 8 to become emitted light 4.

  The principle that the light intensity distribution is shaped simultaneously spatially and temporally by the light intensity distribution shaping device of FIG. 1 will be described with reference to FIGS. Here, FIG. 2 is a conceptual diagram showing the principle that the light intensity distribution is spatially shaped, FIG. 3 is a conceptual diagram showing the principle that the light intensity distribution is temporally shaped, and FIG. 4 is the light intensity. It is a conceptual diagram which shows a mode that distribution is shaped temporally.

  FIG. 2 shows a state in which the branched outgoing lights 5 a to 5 g are emitted from the emission side end face 14 of the bundle fiber 10. Since the cross-sectional diameter of the core layer of each of the optical fibers 10a to 10g is usually about several tens of μm, when the incident light branched by each of the optical fibers 10a to 10g is emitted from the emission side end face 14, it spreads radially by diffraction. Propagate while. As a result, most of the branched outgoing lights 5a to 5g overlap each other, and the spatial nonuniformity is alleviated. Further, the lengths of the optical fibers 10a to 10g are distributed in a predetermined manner as described above. For this reason, the optical path length of the incident light 2 from the incident-side end face 12 to the exit-side end face 14 differs depending on which optical fiber of the optical fibers 10a to 10g the incident light 2 has propagated. Will be distributed. Therefore, since the time for the incident light 2 to propagate from the incident side end face 12 to the emission side end face 14 is also distributed in a predetermined manner, the incident light 2 has a time difference as shown in FIG. Have overlap. As a result, temporal non-uniformity is alleviated.

  These spatial and temporal light intensity distributions are shaped simultaneously. For example, as conceptually shown in FIG. 4, the incident pulse laser light has a three-dimensional intensity distribution close to an elliptical shape, which is advantageous for reducing emittance. It is shaped. Since the length distribution of each of the optical fibers 10a to 10g can take various forms, it can cope with incident light having various light intensity distributions, and the light intensity distributions in various forms can be shaped. Is possible. In particular, if the length of each of the optical fibers 10a to 10g is changed as shown in FIG. 1, the optical path length of the incident light 2 can be greatly changed. Therefore, the incident light having a particularly wide light intensity distribution and the light after shaping. It is possible to cope with the intensity distribution. In addition, it is a very simple and low-cost light intensity distribution shaping device that propagates in the bundle fiber, and there are fewer restrictions on the light wavelength for shaping compared to the conventional method.

  Further, in the light intensity distribution shaping device 1 of FIG. 1, the bundle fiber 10 is disposed in the housing 3, but the bundle fiber 10 is only provided without providing the housing, and the incident-side end surface 12 is the incident surface 6. In this case, the emission side end face 14 may be the emission face 8.

  In the bundle fiber 10 of FIG. 1, the incident side end faces of the optical fibers 10a to 10g are aligned in the same plane. However, the present invention is not limited to such a mode, and as shown in FIG. It is also possible to distribute by shifting in the axial direction. Even in such an aspect, it is possible to give a distribution to the optical path length of incident light propagating in each optical fiber. In addition, when the optical fibers are distributed while being shifted as described above, the length of each optical fiber in the portion excluding the incident side end face portion may be the same, and the length may be further distributed. Also good.

  In the light intensity distribution shaping device described above, the distribution of the length of each optical fiber constituting the bundle fiber has a predetermined distribution in the optical path length of the incident light. It is also possible to give the optical path length a predetermined distribution according to the method. Hereinafter, another method will be described with reference to FIGS. 6 and 7.

  FIG. 6 is a cross-sectional view of a bundle fiber composed of a plurality of types of optical fibers having different relative refractive index differences. The bundle fiber 18 includes four types of optical fibers 18a to 18d having different relative refractive index differences, and these four types of optical fibers are distributed in the bundle fiber in a predetermined manner. Specifically, for example, the relative refractive index differences of the four types of optical fibers 18 a to 18 d are relatively different within a range of 5%, and the optical fiber having the smallest relative refractive index difference is disposed at the center position of the bundle fiber 18. In another optical fiber, the relative refractive index difference of the optical fiber is proportional to the Nth power of the distance from the optical fiber at the center position (N is an integer of 1 or more) or becomes an exponential function of the distance. Distributed. Alternatively, an optical fiber having the largest relative refractive index difference is disposed at the center position of the bundle fiber 18, and the relative refractive index difference of each optical fiber is inversely proportional to the Nth power of the distance from the optical fiber at the center position (as described above). N is an integer equal to or greater than 1, or may be distributed so as to be an exponential function of the distance. As a method of changing the relative refractive index difference, a method of changing the refractive index of both the core layer and the cladding layer, a method of changing the refractive index of the cladding layer with a constant refractive index of the core layer, or a refractive index of the cladding layer being constant. There is a method of changing only the refractive index of the core layer. In FIG. 6, the bundle fiber 18 is configured by four types of optical fibers having a relative refractive index difference, but may be configured by optical fibers having various types of relative refractive index differences.

  Even in such a mode, the refractive index of the core layer of the optical fiber through which the incident light propagates, the distance that the incident light oozes out to the cladding layer, and the total reflection angle are different. It is possible to give the optical path length of incident light a predetermined distribution because of the existence of an optical fiber that propagates and an optical fiber that does not propagate. In this case, it is possible to manufacture a light intensity distribution shaping device having the effects of the present invention by a simple method in which a bundle fiber is configured by a plurality of types of optical fibers having different relative refractive index differences.

  FIG. 7 is a schematic cross-sectional view of a light intensity distribution shaping device when an optical element is used to provide an optical path length distribution. Unlike the light intensity distribution shaping device 1 in FIG. 1, the light intensity distribution shaping device 20 is composed of optical fibers 30 a to 30 g having the same length, and between the incident surface 6 and the incident side end surface 32. An optical element 25 is arranged. In the optical element 25, the optical thickness in the optical axis direction is two-dimensionally distributed in a plane perpendicular to the optical axis. Specifically, for example, the optical element 25 has a constant physical thickness in a plane perpendicular to the optical axis, and is made of a plurality of materials having different refractive indexes. The refractive indexes of the plurality of materials are different within a range of 5%, and the material having the lowest refractive index is disposed in the central portion of the optical element 25. In the other part, the refractive index of the material of the part is proportional to the Nth power of the distance from the center position of the optical element 25 (N is an integer of 1 or more) or becomes an exponential function of the distance. Is distributed. Alternatively, a material having the highest refractive index is disposed in the central portion of the optical element 25, and the refractive index of the other portion is inversely proportional to the Nth power of the distance from the central position of the optical element 25 (N is 1 or more). (Integer) or an exponential function of the distance. Further, in addition to the method of giving the above two-dimensional distribution by changing the refractive index distribution of the material constituting the optical element 25, the in-plane perpendicular to the optical axis of the optical element 25 while keeping the refractive index of the material constant. The method of giving by changing the physical thickness in the method, or the method of giving by changing both the refractive index distribution and the physical thickness of the material may be used.

  In such a configuration, the time required for the incident light 2 to pass through the optical element 25 varies depending on the position in a plane perpendicular to the optical axis of the optical element 25 on which the incident light 2 is incident. Then, the optical fibers 30 a to 30 g constituting the bundle fiber 30 are incident from the incident side end face 32 with a time difference. As a result, the light intensity distribution is shaped spatially and temporally as in the light intensity distribution shaping device of FIG. When a predetermined distribution is given to the optical path length of incident light by this method, there is an advantage that the optical path length distribution can be changed only by replacing the optical element 25. Further, a plurality of optical elements 25 may be arranged between the incident surface 6 and the incident side end surface 32, or one or a plurality of optical elements 25 may be arranged between the emission side end surface 14 and the emission surface 8. 6 and the incident side end face 32 and between the outgoing side end face 14 and the outgoing face 8.

  According to the above-described method for providing a distribution in the optical path length, a method for forming a bundle fiber with an optical fiber having a distribution in length, and an optical fiber having a distribution of a predetermined aspect in a relative refractive index difference. The method of forming the bundle fiber and the method of using the optical element having the distribution of the predetermined form in the two-dimensional optical thickness may be used alone, or two or more arbitrary methods may be combined. Good.

  Next, an application example of the present invention to an electron source will be described with reference to FIG. The cartridge type photocathode 40 is attached to a cylindrical glass 42, Kovar flanges 44 a and 44 b attached to both ends thereof, a bellows 52 arranged coaxially with the cylindrical glass 42, and an end face on one side of the bellows 52. And a transmission type photocathode 54. A Kovar thin film is stretched on the surface of the Kovar flange 44b. In a state before use, the bellows 52 and the transmissive photocathode 54 are vacuum-sealed in the cylindrical glass 42 to prevent the transmissive photocathode 54 from being deteriorated. In use, the cartridge-type photocathode 40 is fixed in the vicinity of the RF cavity end plate 60 provided with a hole having substantially the same size as that of the transmissive photocathode 54 in an apparatus kept in a vacuum. Then, after tearing the Kovar thin film on the surface of the Kovar flanges 44a and 44b with a holding tool (not shown) for breaking the film, the bellows 52 extends beyond the Kovar flange 44b to the RF cavity end plate 60 side, The bellows is fixed in a state where the transmission type photocathode 54 is fitted in a hole provided in the RF cavity end plate 60. Next, the light intensity distribution shaping device 50 according to the present invention incorporating the bundle fiber 56 is passed through the bellows 52 from the Kovar flange 44a and fixed in the vicinity of the transmission type photocathode 54.

  In such an electron source, the laser light incident on the light intensity distribution shaping device is irradiated onto the transmissive photocathode 54 after shaping the appropriate light intensity distribution in time and space. Electrons generated in the RF cavity due to the photoelectric effect are immediately accelerated by the RF electric field to become a low emittance electron beam. If a plurality of cartridge-type photocathodes are prepared in the vacuum apparatus, they can be easily replaced even when the photocathode deteriorates, and it is necessary to provide a film formation apparatus for the photocathode material in the apparatus. Disappears.

  Further, in the light intensity distribution shaping device according to the present invention, since the laser light emitted from the bundle fiber spreads, it is necessary to install the light intensity distribution shaping device in the vicinity of the photocathode. Therefore, in combination with a reflective photocathode, a light intensity distribution shaping device is disposed in a portion to which a strong electric field is applied in order to accelerate electrons, which causes problems such as disturbance of the acceleration electric field. Therefore, in combination with the light intensity distribution shaping device of the present invention, it is preferable to use a transmission type photocathode as shown in FIG.

  Further, when it is necessary to irradiate the photocathode with a laser beam with a small beam diameter, as shown in FIG. 9, a quartz cell 65 containing a liquid with a high refractive index (for example, a liquid used in immersion lithography). Is arranged between the light intensity distribution shaping device 70 and the transmissive photocathode 54. In this case, since the spread of the laser light emitted from the light intensity distribution shaping device 70 is suppressed, the transmission type photocathode 54 can be irradiated with a small beam diameter. Although not shown, there is a method in which an aperture is provided on the incident light side of the transmissive photocathode to fix the beam diameter of the laser beam and at the same time irradiate the transmissive photocathode only with a more uniform central portion.

  The bundle fiber described above may be composed of a normal quartz fiber, but if a photonic crystal fiber, a polarization plane preserving fiber, or the like is used, a wider variety of light intensity distribution shaping becomes possible. For example, when a polarized electron beam is generated by irradiating a polarized laser beam onto a photocathode for a polarized electron source, it is more stable than the conventional method of propagating through space by reflecting with many mirrors. An electron source can be realized. It is also possible to form a hollow fiber having a hollow core and a metal deposited on the cladding surface.

Hereinafter, in order to further clarify the effects of the present invention, description will be made using examples. FIG. 10 shows experimental results obtained by shaping the light intensity distribution using a bundle fiber having a length of 95 cm constituted by 1250 multimode quartz fibers. Here, an experiment was performed using the following two types of bundle fibers.
(1) Mapping method (arrangement method in which all optical fibers have the same length and the positional relationship between both end faces of the optical fiber corresponds one-to-one)
(2) Random system (Random arrangement in which the length of each optical fiber is different, and the positional relationship between both ends of the optical fiber does not correspond)
The random bundle fiber corresponds to the light intensity distribution shaping device 1 shown in FIG. 1, and has a configuration in which the optical path length of incident light is distributed in a predetermined manner.
As shown in FIG. 10, incident light having spatial non-uniformity before entering was overlapped while spreading radially after emission, and the spatial non-uniformity was alleviated. Although the result of FIG. 10 is a case of a random system, the spatial nonuniformity was eased similarly by the mapping system.

  FIG. 11 shows the experimental results obtained by shaping the temporal light intensity distribution using the mapping method and the random type bundle fiber having the same shape as in FIG. When an ultraviolet laser with a pulse width of 5 ps was incident on the FWHM as incident light, the emitted light was shaped into an elliptical shape of 25 ps (FIG. 11 (a)) and 30 ps (FIG. 11 (b)), respectively. Further, as described above, an ideal rectangular shape can be formed by providing a structure having an appropriate optical path length distribution for each three-dimensional light intensity distribution of incident light.

Further, the optimum pulse width can be adjusted by adjusting the length of the bundle fiber.
FIG. 12 shows an experimental result of shaping a temporal light intensity distribution using a random system having the same shape as that of FIG. 10 and a bundle fiber having a length of 95 cm, and a bundle fiber having a random system having a length of 200 cm. It is. When an ultraviolet laser with a pulse width of 80 fs was incident on the FWHM as the incident light, the emitted light was 17 ps at FWHM (FIG. 12 (a) in the case of 95 cm) and 41 ps (in the case of 200 cm, FIG. 12 (b)). Shaped into an oval shape.

  Also, in FIG. 11, it can be seen that incident light emitted from each optical fiber constituting the bundle fiber interferes with each other, and the temporal light intensity distribution of the laser light oscillates periodically. In this case, it is possible to reduce periodic vibration due to optical interference by configuring the bundle fiber with a polarization-preserving fiber and allowing S-polarized light and P-polarized light to alternately enter as incident laser light.

It is a schematic sectional drawing of the light intensity distribution shaping apparatus which concerns on embodiment of this invention. It is a conceptual diagram which shows the principle in which light intensity distribution is shaped spatially. It is a conceptual diagram which shows the principle in which light intensity distribution is shaped temporally. It is a conceptual diagram which shows a mode that light intensity distribution is shaped temporally. It is the schematic of the incident side end surface of the bundle fiber which concerns on embodiment of this invention. It is sectional drawing of the bundle fiber which concerns on embodiment of this invention. It is a schematic sectional drawing of the light intensity distribution shaping apparatus which concerns on embodiment of this invention. It is a schematic sectional drawing of the electron beam generator which concerns on embodiment of this invention. 1 is a partial schematic view of an electron beam generator according to an embodiment of the present invention. It is an experimental result which concerns on embodiment of this invention. It is an experimental result which concerns on embodiment of this invention. It is an experimental result which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20,50,70 ... Light intensity distribution shaping device, 2 ... Incident light, 3 ... Housing, 4 ... Emission light, 5a, 5b, 5c, 5d, 5e, 5f, 5g ... Branched emission light, 6 ... Incident 8, 8, 10, 10, 10 d, 10 e, 10 f, 10 g, 18 a, 18 b, 18 c, 18 d, 30 a, 30 b, 30 c, 30 d, 30e, 30f, 30g ... each optical fiber constituting the bundle fiber, 12, 32 ... incident side end face, 14, 34 ... exit side end face, 25 ... optical element, 40 ... cartridge type photocathode, 42 ... cylindrical glass, 44a , 44b ... Kovar flange, 52 ... Bellows, 54 ... Transmission type photocathode, 60 ... RF cavity end plate, 65 ... Quartz cell containing high refractive index liquid

Claims (5)

In the light intensity distribution shaping device that shapes and emits incident light,
The light intensity distribution shaping device includes a bundle fiber,
The optical path length from the incident surface to the exit surface of the light intensity distribution shaping device of the incident light branched by each optical fiber constituting the bundle fiber is:
The light intensity distribution shaping device, wherein the branched incident light is distributed in a predetermined manner corresponding to a position in the cross-section of the bundle fiber of each optical fiber through which the branched incident light has propagated.   2. The light intensity according to claim 1, wherein the distribution of the predetermined mode is given by changing the length of each optical fiber corresponding to the position in the cross-section of the bundle fiber. Distribution shaping device.   2. The distribution according to claim 1, wherein the distribution of the predetermined mode is given by changing a relative refractive index difference of each optical fiber corresponding to a position in the bundle fiber cross section. Light intensity distribution shaping device. The light intensity distribution shaping device further comprises one or more optical elements,
The optical element is arranged on the side opposite to the traveling direction of the incident light from the incident side end surface of the bundle fiber, or at least one side of the traveling direction side of the incident light from the exit side end surface of the bundle fiber. And
The distribution of the predetermined mode changes the optical thickness in the optical axis direction of the portion corresponding to each optical fiber of the optical element in accordance with the position of the optical fiber in the cross section of the bundle fiber. The light intensity distribution shaping device according to claim 1, wherein the light intensity distribution shaping device is given by: The light intensity distribution shaping device according to any one of claims 1 to 4,
An electron beam generator comprising: a photocathode provided in a traveling direction of outgoing light of the light intensity distribution shaping device.

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