WO2023162391A1 - Laser-accelerated particle beam device and laser-accelerated particle beam generation method - Google Patents

Laser-accelerated particle beam device and laser-accelerated particle beam generation method Download PDF

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WO2023162391A1
WO2023162391A1 PCT/JP2022/044649 JP2022044649W WO2023162391A1 WO 2023162391 A1 WO2023162391 A1 WO 2023162391A1 JP 2022044649 W JP2022044649 W JP 2022044649W WO 2023162391 A1 WO2023162391 A1 WO 2023162391A1
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Prior art keywords
laser
particle beam
aperture mask
aperture
laser light
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PCT/JP2022/044649
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French (fr)
Japanese (ja)
Inventor
信彦 中新
正城 神門
カイ ホァン
康太郎 近藤
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国立研究開発法人量子科学技術研究開発機構
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Publication of WO2023162391A1 publication Critical patent/WO2023162391A1/en

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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K5/00—Irradiation devices
    • G21K5/04—Irradiation devices with beam-forming means
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/06—Electron sources; Electron guns
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/08—Ion sources; Ion guns
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H15/00—Methods or devices for acceleration of charged particles not otherwise provided for, e.g. wakefield accelerators

Definitions

  • the present invention relates to a laser accelerated particle beam device and a laser accelerated particle beam generation method.
  • LPA laser plasma acceleration
  • Non-Patent Document 1 discloses a technique for adjusting the propagation direction of high-intensity laser light in a target by adjusting the angle of an optical element (diffraction grating).
  • the above technique requires time to adjust the angle of the optical element with high precision, and it is difficult to adjust the propagation direction of the laser independently of other parameters. That is, when the angle of the optical element is changed, the focal point of the laser light moves, the focal profile changes, and the state of the generated particle beam often changes significantly.
  • An object of one aspect of the present invention is to provide a laser accelerated particle beam apparatus and a laser accelerated particle beam generation method that reduce fluctuations in the focus position and focus profile when changing the propagation direction of the laser. .
  • a laser accelerated particle beam device that generates a particle beam by exciting a target with a laser beam.
  • an aperture mask having an aperture that partially passes through; and a concave mirror that reflects the laser light that has passed through the aperture of the aperture mask and converges it to a focal point set within the target, wherein the aperture mask It is movable in a direction transverse to laser light passing through the aperture mask.
  • a laser accelerated particle beam device and a laser accelerated particle beam generation method that reduce fluctuations in the focus position and focus profile when changing the propagation direction of the laser.
  • FIG. 1 is a diagram showing a laser accelerated particle beam device according to Embodiment 1 of the present invention
  • FIG. It is a figure showing the detail of an aperture mask. It is a figure showing the relationship between the movement of an aperture mask and the irradiation angle of a laser beam.
  • FIG. 2 is a diagram showing a laser accelerated particle beam device according to Embodiment 2 of the present invention
  • FIG. 4 is a diagram showing a state in which scattered light of laser light propagating in a target is viewed from the lateral direction; It is a figure showing the state which looked at the electron beam emitted from the target from the front. It is a figure showing the energy distribution of an electron beam.
  • FIG. 1 is a diagram showing a laser accelerated particle beam device 10 according to Embodiment 1.
  • FIG. 1A and 1B are respectively a front view and a side view of the laser accelerated particle beam device 10.
  • FIG. X1, Y1, Z1 coordinates and X2, Y2, Z2 coordinates are set with reference to the laser beams L1, L3 (details will be described later).
  • the laser-accelerated particle beam device 10 generates a high-speed (high-energy) particle beam by accelerating particles (eg, electrons, ions) using laser light.
  • the laser accelerated particle beam device 10 has a laser light source 11, an aperture mask 12, a moving mechanism 13, a concave mirror 14, a target 15, fluorescent screens 16a and 16b, imagers 17a, 17b and 17c, and a bending magnet .
  • laser light source 11, aperture mask 12, movement mechanism 13, concave mirror 14, target 15, fluorescent screens 16a, 16b, imagers 17a, 17b, 17c, bending magnet 18 are placed in a vacuum chamber (Fig. not shown) and shielded from the atmosphere.
  • the laser light source 11 causes the laser beam L1 to be incident on the concave mirror 14 .
  • a pulse laser eg, a titanium sapphire laser
  • a titanium sapphire laser can be used.
  • the aperture mask 12 has a substantially flat plate shape and allows part of the laser beam L1 (laser beam L2) emitted from the laser light source 11 to pass through.
  • the aperture mask 12 has a surface perpendicular to the optical axis of the laser beam L1 (the optical axis of the laser beam L2).
  • the aperture mask 12 may be slightly tilted with respect to the optical axis of the laser beam L1 so that part of the laser beam L1 is reflected by the aperture mask 12 and does not return to the laser light source 11 as reflected light.
  • the aperture mask 12 may be curved with respect to the optical axis of the laser beam L ⁇ b>1 so that the reflected light does not return to the laser light source 11 .
  • the aperture mask 12 can be made of, for example, stainless steel, aluminum, Teflon (registered trademark), or the like.
  • the surface of the aperture mask may be uneven so as to diffuse the light.
  • the shape of the laser beam L1 emitted from the laser light source 11 has a certain degree of ambiguity. That is, the low-intensity light spreads around the edge (tail) of the high-intensity light.
  • This low-intensity light component affects the profile of the spot condensed by the concave mirror 14 (condensing profile) and the irradiation angle, and becomes a factor of destabilization of the electron beam.
  • the beam diameter increases, fluctuations in the wavefront of the edge (hem) of the laser beam L1 tend to increase.
  • the fluctuation of the intensity distribution of the spot condensed by the concave mirror 14 increases (unstable condensing profile), and the generated electron beam becomes unstable.
  • the bottom portion of the laser beam (the portion where the wavefront fluctuates greatly) is removed, and the condensing profile of the laser beam is stabilized. As a result, the electron beam itself and its position are stabilized.
  • the aperture mask 12 has a substantially flat plate shape and has an aperture 19 for passing the laser beam L2.
  • the general shape of the opening 19 is circular and has a diameter D smaller than the beam diameter D0 of the laser beam L1. By making the general shape of the opening 19 circular, the diffraction of the laser light caused by the opening 19 can be reduced.
  • the general shape of the opening 19 may be an elliptical shape.
  • This general shape means the general shape of the opening 19 (aperture), and is the shape recognized when separated from the aperture mask 12 to some extent.
  • the edge (inner surface) of the opening 19 is allowed to have a certain amount of unevenness.
  • the shape in which such unevenness is eliminated means the general shape of the opening 19 (opening).
  • abstraction means discarding characteristics other than characteristics that should be abstracted (extracted characteristics). In short, it refers to the shape when the unevenness of the opening edge is ignored.
  • FIG. 2 is a diagram showing the details of the aperture mask 12.
  • FIG. 2A is a front view of the aperture mask 12, and
  • FIG. 2B is an enlarged view of a part (region C) of the aperture mask 12.
  • FIG. 2A is a front view of the aperture mask 12
  • FIG. 2B is an enlarged view of a part (region C) of the aperture mask 12.
  • the edges (inner side surfaces) of the openings 19 have unevenness, for example, a sawtooth (jagged) shape for reducing diffraction of laser light passing through the opening mask 12 .
  • damage to the optical elements, particularly the concave mirror 14, caused by diffraction of the laser from the aperture mask 12 can be further reduced.
  • n number of protrusions 19a and n recesses 19b are alternately arranged.
  • the protrusion 19a protrudes toward the center of the opening 19 (aperture).
  • the recess 19 b is recessed in a direction away from the center of the opening 19 .
  • the tips of the projections 19a are arranged in a substantially circular shape having a diameter D1 with an interval d.
  • the bottom of the recess 19b is arranged in a substantially circular shape with a diameter D2.
  • There is a step G ( (D2-D1)/2) between the convex portion 19a and the concave portion 19b.
  • the diameter D of the opening 19 can be considered to be substantially equal to the intermediate value between the diameters D1 and D2 (D ⁇ (D1+D2)/2).
  • D to D1 means "D ⁇ D1".
  • the number n is too large or too small. If the number n is too large, the distance d will be about the same as or smaller than the wavelength of the laser beam L1. In this case, the edge (inner side surface) of the opening 19 is substantially the same as in the state without irregularities, and the diffracted light is aligned and its intensity is increased. That is, the number n is preferably in a range such that the distance d is sufficiently larger than the wavelength of the laser light. On the other hand, if the number n is too small, even if the distance d is large, the diffracted lights are aligned and the intensity tends to increase. That is, it is preferable that the number n is equal to or greater than a certain number in terms of reducing diffraction.
  • the aperture mask 12 may be arranged in the immediate vicinity of the concave mirror 14.
  • the aperture mask 12 is movable in a direction that traverses the laser beam L2 (laser light) passing through the aperture mask 12 (for example, a direction perpendicular to the optical axis of the laser beam L1 or a direction along the Y1-Z1 plane). As will be described later, by moving the aperture mask 12, it is possible to change the incident angle of the laser beam L3 and thus the emission angle of the high-energy particle beam (here, the electron beam E1). It should be noted that the aperture mask 12 can be made lightweight and movable at high speed.
  • the moving mechanism 13 moves the aperture mask 12 in the direction across the laser beam L1.
  • the moving mechanism 13 is, for example, a driving table that holds the aperture mask 12 and a motor that drives the driving table.
  • the moving mechanism 13 can be controlled from outside the vacuum chamber (not shown).
  • the concave mirror 14 is, for example, an off-axis parabolic mirror (OAP), which reflects the laser beam L2 that has passed through the aperture mask 12 and converges it to the focal point F0.
  • An off-axis parabolic mirror has a surface (off-optical axis paraboloid) that is obtained by cutting a parabolic mirror off its rotation axis (optical axis). Converge incoming light to a focal point.
  • a mirror a plurality of mirrors may be provided for transporting the laser beam L2 to the concave mirror 14, for example.
  • the target 15 is placed at the focal point F0 of the concave mirror 14. That is, the focal point F0 is set within the target 15 .
  • Target 15 is excited by laser beam L3 focused by concave mirror 14 to generate a particle beam.
  • a gas target is used as the target 15, and an electron beam E1 is generated. That is, when a gas target is irradiated with a focused high-intensity laser pulse, electrons in the gas are repelled by the high-intensity laser and a compressional wave of electrons is excited along the propagation direction of the laser. The electrons are accelerated by the high electric field (wake field) due to the density of the electrons. This is called laser wake field acceleration (LWFA). Since the wake field is, for example, a high electric field of 100 [GV/m] or more, it is possible to generate a high-energy (for example, GeV level) electron beam with an acceleration distance of several centimeters.
  • LWFA laser wake field acceleration
  • the fluorescent screen 16a is irradiated with the electron beam E1 from the target 15.
  • the fluorescent screen 16a emits fluorescence P1 by the irradiated electron beam E1, and allows part of the electron beam E1 to pass therethrough as an electron beam E2.
  • the imaging device 17a captures the fluorescence P1 emitted by the fluorescent plate 16a. This makes it possible to observe the electron beam E1 from the front and measure the emission direction and profile of the electron beam E1.
  • the imaging devices 17a to 17c are, for example, image sensors (for example, CMOS cameras).
  • the deflection magnet 18 is a magnet for applying a magnetic field to the electron beam E2 emitted from the fluorescent screen 16a to deflect it.
  • the electron beam E2 is deflected according to its energy.
  • the electron beam E2 deflected by the bending magnet 18 is irradiated onto the fluorescent screen 16b.
  • the fluorescent screen 16b emits fluorescence P2 by the irradiated electron beam E2.
  • the imaging device 17b captures the fluorescence P2 emitted by the fluorescent plate 16b. Thereby, the energy distribution of the electron beam E1 can be measured by observing the deflected electron beam E2 from the front.
  • the imaging device 17c is arranged in the positive direction of the Z2 axis of the target 15 and images the light L4 scattered from the target 15. Thereby, the laser beam L3 in the target 15 can be observed from the lateral direction, and the propagation direction of the laser beam L3 in the target 15 can be measured.
  • the X1, Y1, and Z1 coordinates are set with the laser beam L1 incident on the concave mirror 14 as a reference. That is, the X1 axis is set along the optical axis of the laser beam L1, and the Y1 axis and Z1 axis are set perpendicular to the X1 axis.
  • the plane of the aperture mask 12 is perpendicular to the optical axis of the laser beam L1
  • the Y1 axis and the Z1 axis are set in directions parallel to the plane of the aperture mask 12, and perpendicular to the plane of the aperture mask 12.
  • the X1 axis is set in the direction.
  • the X2, Y2, and Z2 coordinates are set with the laser beam L3 reflected by the concave mirror 14 as a reference. That is, the X2 axis is set along the optical axis A3 of the laser beam L3, and the Y2 axis and Z2 axis are set perpendicular to the X2 axis. The Z2 axis is set parallel to the Z1 axis.
  • an aperture mask whose diameter D of the aperture 19 is smaller than the beam diameter D0 of the laser beam L1 and which is movable in a direction transverse to the laser beam L1. 12 is installed.
  • FIG. 3 is a diagram showing a state in which the aperture mask 12 has been moved.
  • the broken line represents the aperture mask 12 moved by ⁇ Y in the Y1 direction by the moving mechanism 13 .
  • the laser light passing through the aperture mask 12 changes from the laser beam L2 (optical axis A2) to the laser beam L2a (optical axis A2a) substantially parallel to the laser beam L2.
  • both the laser beam L2 and the laser beam L2a are converged to the focal point F0 by the concave mirror 14. This is the same as when a movable mask is placed near the lens and moved.
  • the optical axes of the laser beams L3 and L3a emitted from the concave mirror 14 change from the optical axis A3 to the optical axis A3a. That is, the directions of the optical axes of the laser beams L3 and L3a change by the angle ⁇ between the optical axes A3 and A3a.
  • the maximum change range ⁇ max of the emission angle of the particle beam (electron beam E1) is determined by the beam diameter D0 of the laser beam L1 and the diameter D of the aperture mask 12, as shown in Equation (2).
  • ⁇ max atan((D0 ⁇ D)/Lf) Expression (2)
  • the relationship between the movement amount ⁇ Y of the aperture mask 12 and the angle ⁇ does not necessarily match equation (1).
  • the spatial profile of the laser beam L2 changes.
  • the angle ⁇ changes according to the amount of movement of the position of the center of gravity of the spatial profile.
  • the irradiation position of the laser beam L2 on the concave mirror 14 is changed by moving the position of the aperture mask 12 by the moving mechanism 13 and changing the cutout position of the laser beam L1.
  • the direction of the optical axis A3 of the laser beam L3 focused on the focal point F0 changes.
  • the angle of incidence of the laser beam L2 on the concave mirror 14 does not change.
  • the orientation of the optical axis A3 of the high-intensity laser beam L3 can be adjusted without changing the focal point (and focal profile).
  • the propagation direction of the laser in the target changes, and the emission angle of the particle beam (electron beam E1) from the target 15 also changes.
  • the position and profile of the focal point F0 do not substantially change, the properties (profile) of the particle beam do not change significantly.
  • the irradiation angle (incidence angle) of the laser beam L3 with respect to the target 15, and thus the emission direction of the particle beam (electron beam E1) from the target 15 can be changed. Adjustable. At this time, the position of the focal point F0 and the properties (profile) of the particle beam are held.
  • Adjustment of the irradiation angle (incidence angle) of the laser beam L3 is required in the following cases, for example. Both the incident direction of the laser beam in (1) and the emission direction of the electron beam in (2) can be adjusted by moving the aperture mask 12 . (1) The optical axis of the laser beam L1 is tilted due to the spatial distribution of the intensity of the laser beam L1 from the laser light source 11 and other factors. , or when there is a deviation in the emission direction of the electron beam E1 due to residual angular chirp
  • a part of the laser beam L1 is blocked by the aperture mask 12, and the energy of the laser beam L3 to be irradiated is reduced to some extent. device) can be realized. If the movable range of the electron beam E1 is small, the energy loss is also small.
  • optical elements such as mirrors, diffraction gratings, and concave mirrors 14.
  • the focal point (and focal profile) of the laser beam L3 will change, and the properties of the particle beam will change significantly.
  • the movement mechanism 13 of the aperture mask 12 may be affected by disturbance, the influence of the disturbance is small compared to, for example, the case of driving a mirror.
  • the mirror vibrates during driving, the incident position and incident angle of the laser beam on the concave mirror 14 change at the same time. Therefore, the deviation of the focal point of the laser beam L3 and the deviation of the spot shape occur at the same time, and the generation point, emission direction, and characteristics of the electron beam E1 change.
  • the aperture mask 12 is slightly displaced due to disturbance (vibration, etc.), the condensing point of the laser beam L3, furthermore, the emission point and characteristics of the electron beam E1 do not substantially change (emission point of the electron beam E1). direction changes only slightly).
  • Embodiment 2 A laser accelerated particle beam apparatus 10 according to Embodiment 2 of the present invention will be described in detail below.
  • members having the same functions as the members explained in the first embodiment are denoted by the same reference numerals, and the explanation thereof will not be repeated.
  • a thin film is used as the target 21. That is, the thin-film target 21 is irradiated with the laser beam L3 condensed by the concave mirror 14 to generate the ion beam I1.
  • the use of a thin film target 21 containing carbon allows the generation of a beam of accelerated carbon ions. For example, it can be used for small-sized particle beam cancer therapy equipment.
  • ions are formed along the optical axis A3 of the laser beam L3, and the ions are accelerated by the radiation pressure of the high-intensity laser beam L3 (reaction due to reflection of the laser beam L3), and the ion beam I1 can be
  • This acceleration mechanism is called Radiation Pressure Acceleration.
  • the conditions under which radiation pressure acceleration is possible are generally that the electric field strength of the laser is such that the electrons in the target 21 can be accelerated to relativistic energy (condition 1), and that the thin film target The thickness of 21 is sufficiently small with respect to the laser wavelength (condition 2).
  • Target Normal Sheath Acceleration is generally used as the ion acceleration mechanism.
  • the electrons on the surface of the target 15 are accelerated by a high-intensity laser pulse, and when they escape from the target 21, the electric field (sheath field) generated between them and the target 15 is used to accelerate the ion beam.
  • target vertical sheath field acceleration occurs if the electric field strength of the laser is large enough to accelerate the electrons on the surface of the target 21 to relativistic energies.
  • radiation pressure acceleration is greater than target vertical sheath field acceleration (condition 2 described above).
  • the emission direction of the ion beam I1 changes according to the inclination of the back surface of the target 15. That is, since the sheath field (electric field) is perpendicular to the front surface (back surface) of the target 21 , the emission direction of the ion beam I 1 depends on the inclination of the back surface of the target 21 .
  • the concave mirror 14 for ion acceleration In general, ion acceleration requires convergence of the laser beam L3 to increase its intensity, rather than electron acceleration. For this reason, the concave mirror 14 for ion acceleration generally has a relatively short focal length Lf. However, when the energy of the laser increases, the concave mirror 14 with a relatively long focal length Lf is often used.
  • the high-intensity laser beam L3 can be obtained without substantially moving the condensing point (and the condensing profile). can adjust the direction of the optical axis A3. As a result, the exit direction of the ion beam I1 from the target 21 can be adjusted without substantially changing the profile of the ion beam I1.
  • FIG. 5 is a diagram showing the scattered light seen from the lateral direction when the laser propagates in the target 15.
  • the laser beam L3 is incident from the positive direction of the Y2 axis in (B) and from the negative direction of the Y2 axis in (C).
  • moving the aperture mask 12 slightly changes the direction of the scattered light in the plasma. This is due to the change in the propagation direction (optical axis direction) of the high-intensity laser.
  • FIG. 6 is a diagram showing the state of the electron beam emitted from the target 15 viewed from the front. That is, the electron beam emitted from the plasma in the target 15 was observed by the imaging device 17a. The measurement results of the electron beam profile by the imaging device 17b when the position of the aperture mask 12 is changed are shown.
  • the different profiles P0 to P4 are collectively represented as one. 6, profile P1 is +20 [mm] in the Y1 direction, profile P2 is -20 [mm] in the Y1 direction, profile P3 is -20 [mm] in the Z1 direction, and profile P4 , +20 [mm] in the Z1 direction, and the position of the aperture mask 12 is changed.
  • the center of the electron beam E1 moves in the Y2-axis direction and the Z2-axis direction according to the movement of the aperture mask 12, and the emission direction of the electron beam E1 changes.
  • the profile of the electron beam E1 does not change significantly.
  • FIG. 7 is a diagram showing the energy distribution of the electron beam E2.
  • the electron beam E2 deflected by the deflection magnet 18 was observed by the imaging device 17a.
  • FIG. 7 shows the distribution of the energy EN of the electron beam E2 when the aperture mask 12 is moved.
  • the position of the electron beam E2 changes in the positive and negative directions of the Y2 axis according to the amount of movement of the aperture mask 12.
  • FIG. 7 On the other hand, regarding the energy EN on the horizontal axis, the maximum energy and the energy distribution are within the range of normal energy variation, and the characteristics of the electron beam E2 have not changed significantly.
  • a laser-accelerated particle beam device is a laser-accelerated particle beam device that generates a particle beam by exciting a target with laser light. and a concave mirror that reflects laser light that has passed through the aperture of the aperture mask and converges it to a focal point set within the target, the aperture mask passing through the aperture mask. It is movable in a direction transverse to the laser beam. Accordingly, by moving the aperture mask in a direction across the laser light, the incident direction of the laser light converging on the focal point can be adjusted without substantially moving the convergence point (focus) of the laser light.
  • a laser-accelerated particle beam apparatus comprises a moving mechanism for moving the aperture mask in a direction transverse to laser light passing through the aperture mask. Thereby, the opening mask can be moved by the moving mechanism.
  • the inner surface of the aperture of the aperture mask has irregularities for reducing diffraction of laser light passing through the aperture mask.
  • the inner surface of the opening has a plurality of projections projecting toward the center of the opening.
  • the plurality of projections protruding toward the center of the aperture can reduce damage to optical elements and the like due to diffraction of laser light at the aperture.
  • the general shape of the opening is circular or elliptical.
  • the concave mirror is an off-axis parabolic mirror. Laser light from outside the optical axis of the concave mirror can be converged to the focal point.
  • the particles are electrons or ions. Thereby, electrons or ions can be accelerated using laser light.
  • a method for generating a laser-accelerated particle beam according to the seventh aspect of the present invention includes the step of passing a laser beam through an aperture of an aperture mask; laser light focused to the focal point excites the target to generate a particle beam; and the aperture mask traverses the laser light passing through the aperture. changing the angle of incidence of the laser light converged by the concave mirror on the focal point corresponding to the movement of the aperture mask; and changing the direction of beam emission.
  • the aperture mask in the direction across the laser light, the incident direction of the laser light converging on the focal point can be changed without substantially moving the convergence point (focus) of the laser light, thereby emitting the particle beam. You can adjust the direction.

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Abstract

The present invention provides a laser-accelerated particle beam device and a laser-accelerated particle beam generation method which achieve a reduction in fluctuation of a light focusing position when an irradiation angle is changed. To this end, provided is a laser-accelerated particle beam device (10) that generates a particle beam by exciting a target (15, 21) with laser light, said laser-accelerated particle beam device comprising an aperture mask (12) that has an aperture that allows part of the laser light to pass therethrough, and a concave mirror (14) that reflects the laser light which has passed through the aperture of the aperture mask and causes the laser light to converge at a focal point (F0) set within the target, wherein the aperture mask is movable in a direction that intersects the laser light which passes through the aperture mask.

Description

レーザ加速粒子ビーム装置およびレーザ加速粒子ビーム発生方法Laser accelerated particle beam device and laser accelerated particle beam generation method
　本発明は、レーザ加速粒子ビーム装置およびレーザ加速粒子ビーム発生方法に関する。 The present invention relates to a laser accelerated particle beam device and a laser accelerated particle beam generation method.
　レーザプラズマ粒子加速(Laser plasma acceleration: ＬＰＡ)の技術が知られている。この技術では、凹面鏡によって収束された高強度レーザ光のパルスを標的に照射することで、高度に加速された粒子ビームを生成することができる。例えば、高強度レーザ光のパルスをガス標的に照射することで、ガスがプラズマ化して、電子の粗密波が励起される。この電子の粗密に起因する非常に高い電場(航跡場)によって電子が加速される。 The technology of laser plasma acceleration (LPA) is known. In this technique, a highly accelerated particle beam can be generated by illuminating a target with a pulse of intense laser light focused by a concave mirror. For example, by irradiating a gas target with a pulse of high-intensity laser light, the gas becomes plasma, and compressional waves of electrons are excited. Electrons are accelerated by a very high electric field (wake field) resulting from this density of electrons.
　ここで、粒子ビームを一定の方向に精度良く生成するために、標的中での高強度レーザ光の伝搬方向を高精度で調節できることが好ましい。このため、レーザプラズマ粒子加速において、高強度レーザ光の標的中での伝搬方向を調整する技術が開発されている。例えば、非特許文献１は、光学素子（回折格子）の角度を調節することで、高強度レーザ光の標的中での伝搬方向を調節する技術を開示する。 Here, in order to precisely generate a particle beam in a certain direction, it is preferable to be able to adjust the propagation direction of the high-intensity laser light in the target with high precision. Therefore, in laser plasma particle acceleration, techniques have been developed to adjust the direction of propagation of high-intensity laser light in a target. For example, Non-Patent Document 1 discloses a technique for adjusting the propagation direction of high-intensity laser light in a target by adjusting the angle of an optical element (diffraction grating).
　しかしながら、上述の技術は高精度での光学素子の角度調節に時間を要する上に、レーザの伝搬方向を他のパラメータと独立に調節することが困難である。すなわち、光学素子の角度を変化させると、レーザ光の集光点が移動し、集光プロファイルが変化し、生成される粒子ビームの状態が大きく変化することが多い。 However, the above technique requires time to adjust the angle of the optical element with high precision, and it is difficult to adjust the propagation direction of the laser independently of other parameters. That is, when the angle of the optical element is changed, the focal point of the laser light moves, the focal profile changes, and the state of the generated particle beam often changes significantly.
　本発明の一態様は、レーザの伝搬方向を変化させるときの集光位置や集光プロファイルの変動の低減を図ったレーザ加速粒子ビーム装置およびレーザ加速粒子ビーム発生方法を提供することを目的とする。 An object of one aspect of the present invention is to provide a laser accelerated particle beam apparatus and a laser accelerated particle beam generation method that reduce fluctuations in the focus position and focus profile when changing the propagation direction of the laser. .
　上記の課題を解決するために、本発明の一態様に係るレーザ加速粒子ビーム装置は、レーザ光によって標的を励起することによって、粒子ビームを発生させるレーザ加速粒子ビーム装置であって、レーザ光の一部を通過させる開口を有する開口マスクと、前記開口マスクの開口を通過したレーザ光を反射して、前記標的内に設定された焦点に収束させる凹面鏡と、を備え、前記開口マスクは、前記開口マスクを通過するレーザ光を横切る方向に可動である。 In order to solve the above problems, a laser accelerated particle beam device according to one aspect of the present invention is a laser accelerated particle beam device that generates a particle beam by exciting a target with a laser beam. an aperture mask having an aperture that partially passes through; and a concave mirror that reflects the laser light that has passed through the aperture of the aperture mask and converges it to a focal point set within the target, wherein the aperture mask It is movable in a direction transverse to laser light passing through the aperture mask.
　本発明の一態様によれば、レーザの伝搬方向を変化させるときの集光位置や集光プロファイルの変動の低減を図ったレーザ加速粒子ビーム装置およびレーザ加速粒子ビーム発生方法を提供することができる。 According to one aspect of the present invention, it is possible to provide a laser accelerated particle beam device and a laser accelerated particle beam generation method that reduce fluctuations in the focus position and focus profile when changing the propagation direction of the laser. .
本発明の実施形態１に係るレーザ加速粒子ビーム装置を表す図である。1 is a diagram showing a laser accelerated particle beam device according to Embodiment 1 of the present invention; FIG. 開口マスクの詳細を表す図である。It is a figure showing the detail of an aperture mask. 開口マスクの移動とレーザ光の照射角度の関係を表す図である。It is a figure showing the relationship between the movement of an aperture mask and the irradiation angle of a laser beam. 本発明の実施形態２に係るレーザ加速粒子ビーム装置を表す図である。FIG. 2 is a diagram showing a laser accelerated particle beam device according to Embodiment 2 of the present invention; 標的中で伝搬するレーザ光の散乱光を横方向から見た状態を表す図である。FIG. 4 is a diagram showing a state in which scattered light of laser light propagating in a target is viewed from the lateral direction; 標的から出射する電子ビームを正面から見た状態を表す図である。It is a figure showing the state which looked at the electron beam emitted from the target from the front. 電子ビームのエネルギー分布を表す図である。It is a figure showing the energy distribution of an electron beam.
　〔実施形態１〕
　以下、本発明の実施形態１に係るレーザ加速粒子ビーム装置１０について、詳細に説明する。図１は、実施形態１に係るレーザ加速粒子ビーム装置１０を表す図である。図１の（Ａ）、（Ｂ）はそれぞれ、レーザ加速粒子ビーム装置１０の正面図および側面図である。なお、レーザビームＬ１、Ｌ３を基準として、Ｘ１、Ｙ１、Ｚ１座標、およびＸ２、Ｙ２、Ｚ２座標が設定される（詳細は、後述）。 [Embodiment 1]
Hereinafter, the laser accelerated particle beam device 10 according to Embodiment 1 of the present invention will be described in detail. FIG. 1 is a diagram showing a laser accelerated particle beam device 10 according to Embodiment 1. FIG. 1A and 1B are respectively a front view and a side view of the laser accelerated particle beam device 10. FIG. X1, Y1, Z1 coordinates and X2, Y2, Z2 coordinates are set with reference to the laser beams L1, L3 (details will be described later).
　レーザ加速粒子ビーム装置１０は、レーザ光を用いて、粒子（例えば、電子、イオン）を加速することで、高速（高エネルギー）の粒子ビームを生成する。レーザ加速粒子ビーム装置１０は、レーザ光源１１、開口マスク１２、移動機構１３、凹面鏡１４、標的１５、蛍光板１６ａ、１６ｂ、撮像器１７ａ、１７ｂ、１７ｃ、偏向磁石１８を有する。 The laser-accelerated particle beam device 10 generates a high-speed (high-energy) particle beam by accelerating particles (eg, electrons, ions) using laser light. The laser accelerated particle beam device 10 has a laser light source 11, an aperture mask 12, a moving mechanism 13, a concave mirror 14, a target 15, fluorescent screens 16a and 16b, imagers 17a, 17b and 17c, and a bending magnet .
　これらの要素（レーザ光源１１、開口マスク１２、移動機構１３、凹面鏡１４、標的１５、蛍光板１６ａ、１６ｂ、撮像器１７ａ、１７ｂ、１７ｃ、偏向磁石１８）は、必要に応じて、真空チャンバ（図示せず）内に設置され、大気から遮断される。 These elements (laser light source 11, aperture mask 12, movement mechanism 13, concave mirror 14, target 15, fluorescent screens 16a, 16b, imagers 17a, 17b, 17c, bending magnet 18) are placed in a vacuum chamber (Fig. not shown) and shielded from the atmosphere.
　レーザ光源１１は、凹面鏡１４にレーザビームＬ１を入射させる。レーザ光源１１は、例えば、パルスレーザ（一例として、チタンサファイアレーザ）を用いることができる。 The laser light source 11 causes the laser beam L1 to be incident on the concave mirror 14 . For the laser light source 11, for example, a pulse laser (eg, a titanium sapphire laser) can be used.
　開口マスク１２（アパーチャ）は、略平板形状を有し、レーザ光源１１から出射されるレーザビームＬ１の一部（レーザビームＬ２）を通過させる。開口マスク１２は、レーザビームＬ１の光軸（レーザビームＬ２の光軸）に対して直交する面を有する。但し、レーザビームＬ１の一部が開口マスク１２に反射し、反射光としてレーザ光源１１に戻らないように、開口マスク１２をレーザビームＬ１の光軸に対して、少し傾けてもよい。もしくは、反射光がレーザ光源１１に戻らないように、開口マスク１２はレーザビームＬ１の光軸に対して湾曲状になっていてもよい。開口マスク１２は、例えば、ステンレス、アルミニウム、テフロン（登録商標）などにより構成できる。また、レーザ光源１１への反射光を抑えるため、開口マスクの表面は、光を拡散するように凸凹状であってもよい。  The aperture mask 12 (aperture) has a substantially flat plate shape and allows part of the laser beam L1 (laser beam L2) emitted from the laser light source 11 to pass through. The aperture mask 12 has a surface perpendicular to the optical axis of the laser beam L1 (the optical axis of the laser beam L2). However, the aperture mask 12 may be slightly tilted with respect to the optical axis of the laser beam L1 so that part of the laser beam L1 is reflected by the aperture mask 12 and does not return to the laser light source 11 as reflected light. Alternatively, the aperture mask 12 may be curved with respect to the optical axis of the laser beam L<b>1 so that the reflected light does not return to the laser light source 11 . The aperture mask 12 can be made of, for example, stainless steel, aluminum, Teflon (registered trademark), or the like. Moreover, in order to suppress reflected light to the laser light source 11, the surface of the aperture mask may be uneven so as to diffuse the light. 
　一般に、レーザ光源１１から出射されるレーザビームＬ１の形状は一定の不明確性を有する。すなわち、高強度の光の縁（裾）の周りに低強度の光が広がっている。この低強度の光成分は、凹面鏡１４で集光されたスポットのプロファイル（集光プロファイル）や照射角度に影響を与え、電子ビームの不安定化要因となる。特に、ビーム径が大きくなるにつれて、レーザビームＬ１の縁(裾)の部分の波面のゆらぎが大きくなり易い。この結果、凹面鏡１４で集光されたスポットの強度分布のゆらぎが大きくなり（集光プロファイルの不安定化）、発生する電子ビームが不安定化する。 Generally, the shape of the laser beam L1 emitted from the laser light source 11 has a certain degree of ambiguity. That is, the low-intensity light spreads around the edge (tail) of the high-intensity light. This low-intensity light component affects the profile of the spot condensed by the concave mirror 14 (condensing profile) and the irradiation angle, and becomes a factor of destabilization of the electron beam. In particular, as the beam diameter increases, fluctuations in the wavefront of the edge (hem) of the laser beam L1 tend to increase. As a result, the fluctuation of the intensity distribution of the spot condensed by the concave mirror 14 increases (unstable condensing profile), and the generated electron beam becomes unstable.
　本実施形態では、開口マスク１２を設置することによって、レーザビームの裾の部分（波面のゆらぎの大きい部分）を取り除き、レーザビームの集光プロファイルを安定化している。その結果、電子ビーム自体、およびその位置の安定化が図られる。 In this embodiment, by installing the aperture mask 12, the bottom portion of the laser beam (the portion where the wavefront fluctuates greatly) is removed, and the condensing profile of the laser beam is stabilized. As a result, the electron beam itself and its position are stabilized.
　開口マスク１２は、略平板形状であり、レーザビームＬ２を通過させるための開口部１９を有する。開口部１９の概形は、円形状であり、レーザビームＬ１のビーム径Ｄ０より小さい径Ｄを有する。開口部１９の概形を円形とすることで、開口部１９に起因するレーザ光の回折を低減できる。但し、開口部１９の概形は、楕円形状であってもよい。 The aperture mask 12 has a substantially flat plate shape and has an aperture 19 for passing the laser beam L2. The general shape of the opening 19 is circular and has a diameter D smaller than the beam diameter D0 of the laser beam L1. By making the general shape of the opening 19 circular, the diffraction of the laser light caused by the opening 19 can be reduced. However, the general shape of the opening 19 may be an elliptical shape.
　この概形は、開口部１９（開口）の概略の形状を意味し、開口マスク１２からある程度離間したときに、認識される形状である。次に述べるように、詳細に見れば、開口部１９の縁（内側面）は、一定の凹凸を有することが許容される。いわば、このような凹凸を捨象した形状が、開口部１９（開口）の概形を意味する。ここで、捨象（しゃしょう）とは、抽象（特徴を取り出すこと）すべき特性以外の特性を捨て去ること。要は開口縁の凸凹を無視したときの形状をいう。 This general shape means the general shape of the opening 19 (aperture), and is the shape recognized when separated from the aperture mask 12 to some extent. As will be described below, in detail, the edge (inner surface) of the opening 19 is allowed to have a certain amount of unevenness. In other words, the shape in which such unevenness is eliminated means the general shape of the opening 19 (opening). Here, abstraction means discarding characteristics other than characteristics that should be abstracted (extracted characteristics). In short, it refers to the shape when the unevenness of the opening edge is ignored.
　図２は、開口マスク１２の詳細を表す図である。図２の（Ａ）は、開口マスク１２の正面図であり、図２の（Ｂ）は開口マスク１２の一部（領域Ｃ）の拡大図である。 FIG. 2 is a diagram showing the details of the aperture mask 12. FIG. 2A is a front view of the aperture mask 12, and FIG. 2B is an enlarged view of a part (region C) of the aperture mask 12. FIG.
　ここでは、開口部１９の縁（内側面）が、開口マスク１２を通過するレーザ光の回折を低減するための凹凸、例えば、鋸歯状（ギザギザ）の形状を有する。この結果、開口マスク１２からのレーザの回折による光学素子、特に、凹面鏡１４の損傷をより低減できる。 Here, the edges (inner side surfaces) of the openings 19 have unevenness, for example, a sawtooth (jagged) shape for reducing diffraction of laser light passing through the opening mask 12 . As a result, damage to the optical elements, particularly the concave mirror 14, caused by diffraction of the laser from the aperture mask 12 can be further reduced.
　具体的には、開口部１９の縁（内側面）には、それぞれ個数ｎの凸部１９ａ、凹部１９ｂが交互に配置される。凸部１９ａは、開口部１９（開口）の中心に向かって突出する。凹部１９ｂは、開口部１９の中心から遠ざかる方向に凹む。凸部１９ａの先端は、間隔ｄで径Ｄ１の略円形状に配置される。一方、凹部１９ｂの底は、径Ｄ２の略円形状に配置される。凹部１９ｂの底間は、角度ξを有する。凸部１９ａと凹部１９ｂとの間に、段差Ｇ（＝（Ｄ２－Ｄ１）／２）がある。 Specifically, on the edge (inner side surface) of the opening 19, n number of protrusions 19a and n recesses 19b are alternately arranged. The protrusion 19a protrudes toward the center of the opening 19 (aperture). The recess 19 b is recessed in a direction away from the center of the opening 19 . The tips of the projections 19a are arranged in a substantially circular shape having a diameter D1 with an interval d. On the other hand, the bottom of the recess 19b is arranged in a substantially circular shape with a diameter D2. There is an angle ξ between the bottoms of the recesses 19b. There is a step G (=(D2-D1)/2) between the convex portion 19a and the concave portion 19b.
　ここで、開口部１９の径Ｄは、実質的に径Ｄ１とＤ２の中間値に等しいと考えることができる（Ｄ～（Ｄ１＋Ｄ２）／２）。ここで、「Ｄ～Ｄ１」は「Ｄ≒Ｄ１」を意味する。 Here, the diameter D of the opening 19 can be considered to be substantially equal to the intermediate value between the diameters D1 and D2 (D~(D1+D2)/2). Here, "D to D1" means "D≈D1".
　開口マスク１２からのレーザの回折を低減するためには、個数ｎは、多すぎても、少なすぎても、好ましくない。個数ｎが多すぎると、間隔ｄがレーザビームＬ１の波長と同程度もしくはそれよりも小さくなる。この場合、開口部１９の縁（内側面）は、凹凸のない状態と実質的に変わらなくなり、回折光が揃って、その強度が大きくなる。すなわち、個数ｎは、間隔ｄがレーザ光の波長よりも十分大きくなるような範囲であることが好ましい。一方、個数ｎが少なすぎると、間隔ｄが大きい場合であっても、回折光が揃って、その強度が大きくなり易い。すなわち、個数ｎが一定数以上であることが、回折を低減する上で好ましい。 In order to reduce laser diffraction from the aperture mask 12, it is not preferable that the number n is too large or too small. If the number n is too large, the distance d will be about the same as or smaller than the wavelength of the laser beam L1. In this case, the edge (inner side surface) of the opening 19 is substantially the same as in the state without irregularities, and the diffracted light is aligned and its intensity is increased. That is, the number n is preferably in a range such that the distance d is sufficiently larger than the wavelength of the laser light. On the other hand, if the number n is too small, even if the distance d is large, the diffracted lights are aligned and the intensity tends to increase. That is, it is preferable that the number n is equal to or greater than a certain number in terms of reducing diffraction.
　なお、開口マスク１２から凹面鏡１４までの距離は、ある程度大きいほうが好ましいが、凹面鏡１４の直近に開口マスク１２を配置しても差し支えない。 Although it is preferable that the distance from the aperture mask 12 to the concave mirror 14 is large to some extent, the aperture mask 12 may be arranged in the immediate vicinity of the concave mirror 14.
　開口マスク１２は、開口マスク１２を通過するレーザビームＬ２（レーザ光）を横切る方向（例えば、レーザビームＬ１の光軸に垂直な方向、または、Ｙ１－Ｚ１平面に沿う方向）に可動である。後述のように、開口マスク１２を移動させることで、レーザビームＬ３の入射角度、ひいては高エネルギー粒子ビーム（ここでは、電子ビームＥ１）の出射角度を変化させることができる。なお、開口マスク１２を軽量として、高速で移動可能とすることができる。 The aperture mask 12 is movable in a direction that traverses the laser beam L2 (laser light) passing through the aperture mask 12 (for example, a direction perpendicular to the optical axis of the laser beam L1 or a direction along the Y1-Z1 plane). As will be described later, by moving the aperture mask 12, it is possible to change the incident angle of the laser beam L3 and thus the emission angle of the high-energy particle beam (here, the electron beam E1). It should be noted that the aperture mask 12 can be made lightweight and movable at high speed.
　移動機構１３は、レーザビームＬ１を横切る方向に、開口マスク１２を移動させる。移動機構１３は、例えば、開口マスク１２を保持する駆動テーブルおよび駆動テーブルを駆動するモータである。移動機構１３は、不図示の真空チャンバの外部から制御可能である。 The moving mechanism 13 moves the aperture mask 12 in the direction across the laser beam L1. The moving mechanism 13 is, for example, a driving table that holds the aperture mask 12 and a motor that drives the driving table. The moving mechanism 13 can be controlled from outside the vacuum chamber (not shown).
　凹面鏡１４は、例えば、軸外し放物面鏡（Off-axis parabolic mirror: ＯＡＰ）であり、開口マスク１２を通過したレーザビームＬ２を反射して、焦点Ｆ０に収束させる。軸外し放物面鏡は、放物面鏡をその回転軸（光軸）から外れた箇所で切り取った形状の面（光軸外放物面）を有し、放物面の光軸外から入射する光を焦点に収束させる。なお、凹面鏡１４と開口マスク１２の間に、例えば、レーザビームＬ２を凹面鏡１４まで輸送するためのミラー（複数枚も可）があってもよい。 The concave mirror 14 is, for example, an off-axis parabolic mirror (OAP), which reflects the laser beam L2 that has passed through the aperture mask 12 and converges it to the focal point F0. An off-axis parabolic mirror has a surface (off-optical axis paraboloid) that is obtained by cutting a parabolic mirror off its rotation axis (optical axis). Converge incoming light to a focal point. Between the concave mirror 14 and the aperture mask 12, there may be a mirror (a plurality of mirrors may be provided) for transporting the laser beam L2 to the concave mirror 14, for example.
　標的１５は、凹面鏡１４の焦点Ｆ０に配置される。すなわち、焦点Ｆ０は、標的１５内に設定される。標的１５は、凹面鏡１４によって収束されたレーザビームＬ３によって励起されて、粒子ビームを発生する。 The target 15 is placed at the focal point F0 of the concave mirror 14. That is, the focal point F0 is set within the target 15 . Target 15 is excited by laser beam L3 focused by concave mirror 14 to generate a particle beam.
　ここでは、標的１５として、ガス標的を用い、電子ビームＥ１を発生させる。すなわち、収束された高強度のレーザパルスをガス標的に照射すると、ガス中の電子が高強度レーザによって排斥され、レーザの伝搬方向に沿う、電子の粗密波が励起される。この電子の粗密による高電場(航跡場)によって電子を加速する。これをレーザ航跡場加速(Laser wake field acceleration: ＬＷＦＡ)と呼ぶ。航跡場は、例えば、１００［ＧＶ／ｍ］以上の高電場であることから、数ｃｍ程度の加速距離で、高エネルギー（例えば、ＧｅＶレベル）の電子ビームを発生することができる。 Here, a gas target is used as the target 15, and an electron beam E1 is generated. That is, when a gas target is irradiated with a focused high-intensity laser pulse, electrons in the gas are repelled by the high-intensity laser and a compressional wave of electrons is excited along the propagation direction of the laser. The electrons are accelerated by the high electric field (wake field) due to the density of the electrons. This is called laser wake field acceleration (LWFA). Since the wake field is, for example, a high electric field of 100 [GV/m] or more, it is possible to generate a high-energy (for example, GeV level) electron beam with an acceleration distance of several centimeters.
　蛍光板１６ａには、標的１５からの電子ビームＥ１が照射される。蛍光板１６ａは、照射された電子ビームＥ１によって、蛍光Ｐ１を発すると共に、電子ビームＥ１の一部を電子ビームＥ２として通過させる。 The fluorescent screen 16a is irradiated with the electron beam E1 from the target 15. The fluorescent screen 16a emits fluorescence P1 by the irradiated electron beam E1, and allows part of the electron beam E1 to pass therethrough as an electron beam E2.
　撮像器１７ａは、蛍光板１６ａが発した蛍光Ｐ１を撮像する。これにより、電子ビームＥ１を正面から観察して、電子ビームＥ１の出射方向およびプロファイルを計測できる。なお、撮像器１７ａ～１７ｃは、例えば、イメージセンサ（一例として、ＣＭＯＳカメラ）である。 The imaging device 17a captures the fluorescence P1 emitted by the fluorescent plate 16a. This makes it possible to observe the electron beam E1 from the front and measure the emission direction and profile of the electron beam E1. The imaging devices 17a to 17c are, for example, image sensors (for example, CMOS cameras).
　偏向磁石１８は、蛍光板１６ａから出射される電子ビームＥ２に磁場を印可して偏向させるための磁石である。電子ビームＥ２は、そのエネルギーに応じて、偏向する。 The deflection magnet 18 is a magnet for applying a magnetic field to the electron beam E2 emitted from the fluorescent screen 16a to deflect it. The electron beam E2 is deflected according to its energy.
　蛍光板１６ｂには、偏向磁石１８によって偏向された電子ビームＥ２が照射される。蛍光板１６ｂは、照射された電子ビームＥ２によって、蛍光Ｐ２を発する。 The electron beam E2 deflected by the bending magnet 18 is irradiated onto the fluorescent screen 16b. The fluorescent screen 16b emits fluorescence P2 by the irradiated electron beam E2.
　撮像器１７ｂは、蛍光板１６ｂが発した蛍光Ｐ２を撮像する。これにより、偏向された電子ビームＥ２を正面から観察して、電子ビームＥ１のエネルギー分布を計測できる。 The imaging device 17b captures the fluorescence P2 emitted by the fluorescent plate 16b. Thereby, the energy distribution of the electron beam E1 can be measured by observing the deflected electron beam E2 from the front.
　撮像器１７ｃは、標的１５のＺ２軸の正方向に配置され、標的１５から散乱される光Ｌ４を撮像する。これにより、標的１５中のレーザビームＬ３を横方向から観察して、標的１５中でのレーザビームＬ３の伝搬方向を計測できる。 The imaging device 17c is arranged in the positive direction of the Z2 axis of the target 15 and images the light L4 scattered from the target 15. Thereby, the laser beam L3 in the target 15 can be observed from the lateral direction, and the propagation direction of the laser beam L3 in the target 15 can be measured.
　ここで、凹面鏡１４に入射されるレーザビームＬ１を基準として、Ｘ１、Ｙ１、Ｚ１座標が設定される。すなわち、レーザビームＬ１の光軸に沿ってＸ１軸が設定され、Ｘ１軸と垂直にＹ１軸、Ｚ１軸が設定される。ここでは、開口マスク１２の面がレーザビームＬ１の光軸と垂直であることから、開口マスク１２の面に平行な方向にＹ１軸、およびＺ１軸が設定され、開口マスク１２の面に垂直な方向にＸ１軸が設定される。 Here, the X1, Y1, and Z1 coordinates are set with the laser beam L1 incident on the concave mirror 14 as a reference. That is, the X1 axis is set along the optical axis of the laser beam L1, and the Y1 axis and Z1 axis are set perpendicular to the X1 axis. Here, since the plane of the aperture mask 12 is perpendicular to the optical axis of the laser beam L1, the Y1 axis and the Z1 axis are set in directions parallel to the plane of the aperture mask 12, and perpendicular to the plane of the aperture mask 12. The X1 axis is set in the direction.
　また、凹面鏡１４によって反射されるレーザビームＬ３を基準として、Ｘ２、Ｙ２、Ｚ２座標が設定される。すなわち、レーザビームＬ３の光軸Ａ３に沿ってＸ２軸が設定され、Ｘ２軸と垂直にＹ２軸、Ｚ２軸が設定される。Ｚ２軸は、Ｚ１軸と平行に設定される。 Also, the X2, Y2, and Z2 coordinates are set with the laser beam L3 reflected by the concave mirror 14 as a reference. That is, the X2 axis is set along the optical axis A3 of the laser beam L3, and the Y2 axis and Z2 axis are set perpendicular to the X2 axis. The Z2 axis is set parallel to the Z1 axis.
　本実施形態では、レーザビームＬ１の光路上、凹面鏡１４の前に、レーザビームＬ１のビーム径Ｄ０に対して、開口部１９の口径Ｄが小さく、レーザビームＬ１を横切る方向に移動可能な開口マスク１２を設置する。この結果、次に示すように、開口マスク１２を移動することによって、高エネルギー粒子（ここでは、電子ビーム）の出射方向を制御できる。 In this embodiment, on the optical path of the laser beam L1, in front of the concave mirror 14, there is provided an aperture mask whose diameter D of the aperture 19 is smaller than the beam diameter D0 of the laser beam L1 and which is movable in a direction transverse to the laser beam L1. 12 is installed. As a result, by moving the aperture mask 12, the emission direction of the high-energy particles (here, the electron beam) can be controlled as described below.
　図３は、開口マスク１２を移動させた状態を表す図である。移動機構１３によって開口マスク１２をＹ１方向にΔＹだけ移動させた開口マスク１２を破線で表す。 FIG. 3 is a diagram showing a state in which the aperture mask 12 has been moved. The broken line represents the aperture mask 12 moved by ΔY in the Y1 direction by the moving mechanism 13 .
　開口マスク１２が移動することで、開口マスク１２を通過するレーザ光は、レーザビームＬ２（光軸Ａ２）から、レーザビームＬ２に略平行なレーザビームＬ２ａ（光軸Ａ２ａ）へと変化する。 By moving the aperture mask 12, the laser light passing through the aperture mask 12 changes from the laser beam L2 (optical axis A2) to the laser beam L2a (optical axis A2a) substantially parallel to the laser beam L2.
　ここで、レーザビームＬ２およびレーザビームＬ２ａはいずれも、凹面鏡１４によって焦点Ｆ０に収束される。この点は、レンズの近くに、移動可能なマスクを配置し、移動させた場合と同様である。 Here, both the laser beam L2 and the laser beam L2a are converged to the focal point F0 by the concave mirror 14. This is the same as when a movable mask is placed near the lens and moved.
　開口マスク１２をＹ１方向にΔＹだけ移動させることで、凹面鏡１４から出射されるレーザビームＬ３、Ｌ３ａの光軸は、光軸Ａ３から光軸Ａ３ａへと変化する。すなわち、レーザビームＬ３、Ｌ３ａの光軸の方向は、光軸Ａ３、Ａ３ａのなす角度θだけ、変化する。この角度θは、レーザビームＬ１の強度プロファイルが均一な場合、次の式（１）によって表すことができる。
　　θ＝ａｔａｎ（ΔＹ／Ｌｆ）　……式（１） By moving the aperture mask 12 by ΔY in the Y1 direction, the optical axes of the laser beams L3 and L3a emitted from the concave mirror 14 change from the optical axis A3 to the optical axis A3a. That is, the directions of the optical axes of the laser beams L3 and L3a change by the angle θ between the optical axes A3 and A3a. This angle θ can be expressed by the following equation (1) when the intensity profile of the laser beam L1 is uniform.
θ=a tan (ΔY/Lf) Equation (1)
　なお、粒子ビーム（電子ビームＥ１）の出射角度の最大変化範囲θｍａｘは、式（２）に示すように、レーザビームＬ１のビーム径Ｄ０と開口マスク１２の径Ｄより定まる。
　　θｍａｘ＝ａｔａｎ（（Ｄ０－Ｄ）/Ｌｆ）　……式（２） The maximum change range θmax of the emission angle of the particle beam (electron beam E1) is determined by the beam diameter D0 of the laser beam L1 and the diameter D of the aperture mask 12, as shown in Equation (2).
θmax=atan((D0−D)/Lf) Expression (2)
　一方、レーザビームＬ１の強度プロファイルが一様ではない場合、開口マスク１２の移動量ΔＹと角度θの関係は、式（１）と必ずしも一致しない。この場合、開口マスク１２が移動すると、レーザビームＬ２の空間プロファイルが変化する。そして、この空間プロファイルの重心位置の移動量に応じて、角度θは変化する。 On the other hand, if the intensity profile of the laser beam L1 is not uniform, the relationship between the movement amount ΔY of the aperture mask 12 and the angle θ does not necessarily match equation (1). In this case, when the aperture mask 12 moves, the spatial profile of the laser beam L2 changes. The angle θ changes according to the amount of movement of the position of the center of gravity of the spatial profile.
　以上のように、移動機構１３によって開口マスク１２の位置を動かし、レーザビームＬ１の切り出す場所を変えることにより、凹面鏡１４へのレーザビームＬ２の照射位置が変化する。この結果、焦点Ｆ０に集光するレーザビームＬ３の光軸Ａ３の方向が変化する。このとき、レーザビームＬ２の凹面鏡１４への入射角度は変化しない。この結果、集光点（および集光プロファイル）を変えずに、高強度のレーザビームＬ３の光軸Ａ３の向きを調整できる。 As described above, the irradiation position of the laser beam L2 on the concave mirror 14 is changed by moving the position of the aperture mask 12 by the moving mechanism 13 and changing the cutout position of the laser beam L1. As a result, the direction of the optical axis A3 of the laser beam L3 focused on the focal point F0 changes. At this time, the angle of incidence of the laser beam L2 on the concave mirror 14 does not change. As a result, the orientation of the optical axis A3 of the high-intensity laser beam L3 can be adjusted without changing the focal point (and focal profile).
　標的１５に対するレーザビームＬ３の照射角度（入射角度）が、変化することで、標的中でのレーザの伝搬方向が変化し、標的１５からの粒子ビーム（電子ビームＥ１）の出射角度も変化する。このとき、焦点Ｆ０の位置およびプロファイルは実質的に変化しないことから、粒子ビームの特性（プロファイル）が大きく変化することはない。 By changing the irradiation angle (incident angle) of the laser beam L3 with respect to the target 15, the propagation direction of the laser in the target changes, and the emission angle of the particle beam (electron beam E1) from the target 15 also changes. At this time, since the position and profile of the focal point F0 do not substantially change, the properties (profile) of the particle beam do not change significantly.
　以上のように、本実施形態では、開口マスク１２を移動させることで、標的１５に対するレーザビームＬ３の照射角度（入射角度）、ひいては、標的１５からの粒子ビーム（電子ビームＥ１）の出射方向を調節できる。このとき、焦点Ｆ０の位置、粒子ビームの特性（プロファイル）は保持される。 As described above, in the present embodiment, by moving the aperture mask 12, the irradiation angle (incidence angle) of the laser beam L3 with respect to the target 15, and thus the emission direction of the particle beam (electron beam E1) from the target 15 can be changed. Adjustable. At this time, the position of the focal point F0 and the properties (profile) of the particle beam are held.
　レーザビームＬ３の照射角度（入射角度）の調節は、例えば、次のような場合に、必要となる。次の（１）でのレーザビームの入射方向、（２）での電子ビームの出射方向のいずれも、開口マスク１２の移動によって、調節可能である。
（１）レーザ光源１１からのレーザビームＬ１の強度の空間分布、その他の要因によって、レーザビームＬ１の光軸が傾いている場合
（２）集光前のレーザビームＬ２の空間プロファイルの強度の偏り、または角度チャープの残存に起因して、電子ビームＥ１の出射方向にずれがある場合 Adjustment of the irradiation angle (incidence angle) of the laser beam L3 is required in the following cases, for example. Both the incident direction of the laser beam in (1) and the emission direction of the electron beam in (2) can be adjusted by moving the aperture mask 12 .
(1) The optical axis of the laser beam L1 is tilted due to the spatial distribution of the intensity of the laser beam L1 from the laser light source 11 and other factors. , or when there is a deviation in the emission direction of the electron beam E1 due to residual angular chirp
　開口マスク１２によって、レーザビームＬ１の一部が遮られ、照射するレーザビームＬ３のエネルギーがある程度小さくなるが、安定性と制御・操作性を兼ね備えたロバストな粒子ビーム方向制御装置（レーザ加速粒子ビーム装置）を実現できる。なお、電子ビームＥ１の可動範囲が小さくてよければ、エネルギー損失も小さい。 A part of the laser beam L1 is blocked by the aperture mask 12, and the energy of the laser beam L3 to be irradiated is reduced to some extent. device) can be realized. If the movable range of the electron beam E1 is small, the energy loss is also small.
　ミラー、回折格子、凹面鏡１４等の光学素子を操作して、レーザビームＬ３の光軸Ａ３の方向を調節することも可能である。しかし、この場合、レーザビームＬ３の集光点（および集光プロファイル）が変化し、粒子ビームの特性が大きく変化することになる。 It is also possible to adjust the direction of the optical axis A3 of the laser beam L3 by operating optical elements such as mirrors, diffraction gratings, and concave mirrors 14. However, in this case, the focal point (and focal profile) of the laser beam L3 will change, and the properties of the particle beam will change significantly.
　開口マスク１２の移動機構１３は、外乱の影響を受ける可能性があるが、例えば、ミラーを駆動する場合に比べて、外乱の影響は小さい。駆動時にミラーが振動すると、凹面鏡１４へのレーザ光の入射位置および入射角度が同時に変化する。このため、レーザビームＬ３の集光点のずれとスポット形状のくずれが同時に起こり、電子ビームＥ１の発生点、出射方向、および特性が変化する。開口マスク１２は、外乱（振動等）によって微小に変位しても、レーザビームＬ３の集光点、さらには、電子ビームＥ１の発生点、特性は、実質的に変化しない（電子ビームＥ１の出射方向が微小に変化するに留まる）。 Although the movement mechanism 13 of the aperture mask 12 may be affected by disturbance, the influence of the disturbance is small compared to, for example, the case of driving a mirror. When the mirror vibrates during driving, the incident position and incident angle of the laser beam on the concave mirror 14 change at the same time. Therefore, the deviation of the focal point of the laser beam L3 and the deviation of the spot shape occur at the same time, and the generation point, emission direction, and characteristics of the electron beam E1 change. Even if the aperture mask 12 is slightly displaced due to disturbance (vibration, etc.), the condensing point of the laser beam L3, furthermore, the emission point and characteristics of the electron beam E1 do not substantially change (emission point of the electron beam E1). direction changes only slightly).
　レーザ航跡場加速では約８［ＧｅＶ］の高エネルギー電子ビームの発生が可能であり、本実施形態の技術によって、ＧｅＶ級の高エネルギー電子ビームの方向操作が可能となる。すなわち、多段階のレーザ航跡場加速によって、高エネルギー化を図ることができる。この場合、前段の航跡場から出てきた電子ビームを後段の航跡場に精度よく入射する必要がある。航跡場は、一般に、微小（数十μｍ以下）であり、電子ビームの高精度での入射は容易ではない。本実施形態の技術によって、このような高精度での入射が可能となる。 With laser wake field acceleration, it is possible to generate a high-energy electron beam of about 8 [GeV], and the technology of this embodiment makes it possible to control the direction of a GeV-class high-energy electron beam. That is, it is possible to increase the energy by multi-stage laser wake field acceleration. In this case, it is necessary to make the electron beam emitted from the former wake field accurately enter the latter wake field. The wake field is generally very small (several tens of micrometers or less), and it is not easy to make the electron beams enter with high precision. The technique of the present embodiment enables such highly accurate incidence.
　以上のように、本実施形態の技術を用いて、粒子ビーム（例えば、電子ビーム）の位置および方向を高精度で制御可能となり、例えば、レーザ航跡場加速の電子ビームを利用した小型自由電子レーザ、高速電子顕微鏡を実現できる。 As described above, using the technology of the present embodiment, it is possible to control the position and direction of a particle beam (for example, an electron beam) with high precision. , which can realize high-speed electron microscopy.
　〔実施形態２〕
　以下、本発明の実施形態２に係るレーザ加速粒子ビーム装置１０について、詳細に説明する。なお、説明の便宜上、上記実施形態１にて説明した部材と同じ機能を有する部材については、同じ符号を付記し、その説明を繰り返さない。 [Embodiment 2]
A laser accelerated particle beam apparatus 10 according to Embodiment 2 of the present invention will be described in detail below. For convenience of explanation, members having the same functions as the members explained in the first embodiment are denoted by the same reference numerals, and the explanation thereof will not be repeated.
　ここでは、標的２１として、薄膜を用いる。すなわち、凹面鏡１４で集光したレーザビームＬ３を薄膜の標的２１に照射して、イオンビームＩ１を発生させる。例えば、炭素を含む薄膜の標的２１を用いることで、加速された炭素イオンのビームの生成が可能となる。例えば、小型の粒子線がん治療装置への利用が可能となる。 Here, a thin film is used as the target 21. That is, the thin-film target 21 is irradiated with the laser beam L3 condensed by the concave mirror 14 to generate the ion beam I1. For example, the use of a thin film target 21 containing carbon allows the generation of a beam of accelerated carbon ions. For example, it can be used for small-sized particle beam cancer therapy equipment.
　具体的には、レーザビームＬ３の光軸Ａ３に沿って、イオンが形成され、そのイオンを高強度のレーザビームＬ３の放射圧（レーザビームＬ３の反射による反作用）によって、加速し、イオンビームＩ１とすることができる。この加速の機構を放射圧加速(Radiation Pressure Acceleration)という。ここで、放射圧加速が可能な条件は、一般に、レーザの電場強度が標的２１の電子を相対論的なエネルギーまで加速することが可能な強度であること（条件１）、および、薄膜の標的２１の厚みがレーザ波長に対して十分小さいこと（条件２）である。 Specifically, ions are formed along the optical axis A3 of the laser beam L3, and the ions are accelerated by the radiation pressure of the high-intensity laser beam L3 (reaction due to reflection of the laser beam L3), and the ion beam I1 can be This acceleration mechanism is called Radiation Pressure Acceleration. Here, the conditions under which radiation pressure acceleration is possible are generally that the electric field strength of the laser is such that the electrons in the target 21 can be accelerated to relativistic energy (condition 1), and that the thin film target The thickness of 21 is sufficiently small with respect to the laser wavelength (condition 2).
　イオンの加速の機構としては、一般には、ターゲット垂直シース場加速(Target Normal Sheath Acceleration)が、利用される。この手法は、高強度レーザパルスによって標的１５の表面の電子が加速されて、標的２１から抜け出るときに、標的１５との間で発生する電場（シース場）を利用して、イオンビームを加速する。ここで、レーザの電場強度が、標的２１表面の電子を相対論的なエネルギーまで加速可能な程度に大きければ、ターゲット垂直シース場加速が生じる。但し、標的２１の厚みが薄い場合、ターゲット垂直シース場加速よりも、放射圧加速が大きくなる（前述の条件２）。 Target Normal Sheath Acceleration is generally used as the ion acceleration mechanism. In this method, the electrons on the surface of the target 15 are accelerated by a high-intensity laser pulse, and when they escape from the target 21, the electric field (sheath field) generated between them and the target 15 is used to accelerate the ion beam. . Here, target vertical sheath field acceleration occurs if the electric field strength of the laser is large enough to accelerate the electrons on the surface of the target 21 to relativistic energies. However, when the thickness of the target 21 is thin, radiation pressure acceleration is greater than target vertical sheath field acceleration (condition 2 described above).
　しかし、ターゲット垂直シース場加速の手法は標的１５の裏面の傾きに応じて、イオンビームＩ１の出射方向が変化するため、本実施形態への適用は困難である。すなわち、シース場（電場）は、標的２１の表面（裏面）に垂直であるため、イオンビームＩ１の出射方向は、標的２１の裏面の傾きに依存する。 However, it is difficult to apply the method of target vertical sheath field acceleration to this embodiment because the emission direction of the ion beam I1 changes according to the inclination of the back surface of the target 15. That is, since the sheath field (electric field) is perpendicular to the front surface (back surface) of the target 21 , the emission direction of the ion beam I 1 depends on the inclination of the back surface of the target 21 .
　一般に、イオン加速においては、電子加速よりも、レーザビームＬ３を収束させて、その強度を大きくすることが必要とされる。このため、一般に、イオン加速用の凹面鏡１４は、比較的短い焦点距離Ｌｆを有する。但し、レーザのエネルギーが大きくなると、ある程度長い焦点距離Ｌｆの凹面鏡１４を用いることが多い。 In general, ion acceleration requires convergence of the laser beam L3 to increase its intensity, rather than electron acceleration. For this reason, the concave mirror 14 for ion acceleration generally has a relatively short focal length Lf. However, when the energy of the laser increases, the concave mirror 14 with a relatively long focal length Lf is often used.
　以上のように、本実施形態においても、実施形態１と同様、開口マスク１２の位置を動かすことにより、集光点（および集光プロファイル）を実質的に動かすことなく、高強度のレーザビームＬ３の光軸Ａ３の向きを調整できる。その結果、イオンビームＩ１のプロファイルを実質的に変化させることなく、標的２１からのイオンビームＩ１の出射方向を調節できる。 As described above, in the present embodiment, similarly to the first embodiment, by moving the position of the aperture mask 12, the high-intensity laser beam L3 can be obtained without substantially moving the condensing point (and the condensing profile). can adjust the direction of the optical axis A3. As a result, the exit direction of the ion beam I1 from the target 21 can be adjusted without substantially changing the profile of the ion beam I1.
（実験結果）
　以下、実験結果を説明する。レーザ光源１１として、次の仕様のチタンサファイアレーザを用いた。すなわち、中心波長：８１０［ｎｍ］、パルス幅：４０［ｆｓ］、エネルギー：２０［Ｊ］、ビーム径：φ２６［ｃｍ］とした。また、開口マスク１２の開口部１９の径Ｄを１３［ｃｍ］とした。 (Experimental result)
Experimental results are described below. As the laser light source 11, a titanium sapphire laser having the following specifications was used. That is, center wavelength: 810 [nm], pulse width: 40 [fs], energy: 20 [J], beam diameter: φ26 [cm]. Also, the diameter D of the opening 19 of the opening mask 12 was set to 13 [cm].
　図５は、標的１５の中でレーザが伝搬するときの散乱光を横方向から見た状態を表す図である。すなわち、レーザビームＬ３によって励起された標的１５中のプラズマから散乱する光を撮像器１７ｃによって観察した。図５の（Ａ）に対して、Ｙ１軸方向に、（Ｂ）では、＋２０［ｍｍ］（正方向に）、（Ｃ）では、－２０［ｍｍ］（負方向に）、開口マスク１２の位置を変化させている。この結果、（Ｂ）では、Ｙ２軸の正方向から、（Ｃ）では、Ｙ２軸の負方向から、レーザビームＬ３が入射する。このように、開口マスク１２を移動させると、プラズマ中での散乱光の向きが幾分変化する。これは高強度レーザの伝搬方向（光軸の方向）が変化していることに起因する。 FIG. 5 is a diagram showing the scattered light seen from the lateral direction when the laser propagates in the target 15. FIG. That is, the light scattered from the plasma in the target 15 excited by the laser beam L3 was observed by the imager 17c. 5A, in the Y1 axis direction, +20 [mm] (in the positive direction) in FIG. changing position. As a result, the laser beam L3 is incident from the positive direction of the Y2 axis in (B) and from the negative direction of the Y2 axis in (C). Thus, moving the aperture mask 12 slightly changes the direction of the scattered light in the plasma. This is due to the change in the propagation direction (optical axis direction) of the high-intensity laser.
　図６は、標的１５から出射する電子ビームを正面から見た状態を表す図である。すなわち、標的１５中のプラズマから出射する電子ビームを撮像器１７ａによって観察した。開口マスク１２の位置を変化させたときの、撮像器１７ｂによる電子ビームのプロファイルの計測結果が示される。ここでは、分かり易さのために、異なるプロファイルＰ０～Ｐ４を１つに纏めて表している。図６のプロファイルＰ０に対して、プロファイルＰ１では、Ｙ１方向に＋２０［ｍｍ］、プロファイルＰ２では、Ｙ１方向に－２０［ｍｍ］、プロファイルＰ３では、Ｚ１方向に－２０［ｍｍ］、プロファイルＰ４では、Ｚ１方向に＋２０［ｍｍ］、開口マスク１２の位置を変化させている。 FIG. 6 is a diagram showing the state of the electron beam emitted from the target 15 viewed from the front. That is, the electron beam emitted from the plasma in the target 15 was observed by the imaging device 17a. The measurement results of the electron beam profile by the imaging device 17b when the position of the aperture mask 12 is changed are shown. Here, for ease of understanding, the different profiles P0 to P4 are collectively represented as one. 6, profile P1 is +20 [mm] in the Y1 direction, profile P2 is -20 [mm] in the Y1 direction, profile P3 is -20 [mm] in the Z1 direction, and profile P4 , +20 [mm] in the Z1 direction, and the position of the aperture mask 12 is changed.
　開口マスク１２の移動に応じて、電子ビームＥ１の中心がＹ２軸方向、Ｚ２軸方向に移動し、電子ビームＥ１の出射方向が変化していることが分かる。この一方、電子ビームＥ１のプロファイルは大きく変化してはいない。 It can be seen that the center of the electron beam E1 moves in the Y2-axis direction and the Z2-axis direction according to the movement of the aperture mask 12, and the emission direction of the electron beam E1 changes. On the other hand, the profile of the electron beam E1 does not change significantly.
　図７は、電子ビームＥ２のエネルギー分布を表す図である。偏向磁石１８によって偏向された電子ビームＥ２を撮像器１７ａによって観測した。図７の（Ａ）に対して、Ｚ１軸方向に、（Ｂ）では、＋２０［ｍｍ］（正方向に）、（Ｃ）では、－２０［ｍｍ］（負方向に）、開口マスク１２の位置を変化させている。図７は、開口マスク１２を移動させたときの、電子ビームＥ２のエネルギーＥＮの分布を示す。開口マスク１２の移動量に応じて電子ビームＥ２の位置がＹ２軸の正負の方向に変化している。一方、横軸のエネルギーＥＮについては、最大エネルギー、およびエネルギー分布が、通常のエネルギーのバラツキの範囲に収まっており、電子ビームＥ２の特性は大きくは変化していない。 FIG. 7 is a diagram showing the energy distribution of the electron beam E2. The electron beam E2 deflected by the deflection magnet 18 was observed by the imaging device 17a. With respect to (A) of FIG. 7, in the Z1 axis direction, in (B) +20 [mm] (in the positive direction), in (C) -20 [mm] (in the negative direction), the opening mask 12 changing position. FIG. 7 shows the distribution of the energy EN of the electron beam E2 when the aperture mask 12 is moved. The position of the electron beam E2 changes in the positive and negative directions of the Y2 axis according to the amount of movement of the aperture mask 12. FIG. On the other hand, regarding the energy EN on the horizontal axis, the maximum energy and the energy distribution are within the range of normal energy variation, and the characteristics of the electron beam E2 have not changed significantly.
　以上の実験結果から次のことが言える。すなわち、開口マスク１２の位置を変化させることで、標的１５中でのレーザビームＬ３の伝搬方向（入射方向）、および電子ビームＥ１の発生方向（出射方向）が変化する。このとき、電子ビームＥ１の特性およびプロファイルは実質的に変化していない。 From the above experimental results, the following can be said. That is, by changing the position of the aperture mask 12, the propagation direction (incident direction) of the laser beam L3 in the target 15 and the generation direction (emission direction) of the electron beam E1 are changed. At this time, the characteristics and profile of the electron beam E1 are substantially unchanged.
（上記実施形態実施形態１、２から把握される発明）
　以下、上記実施形態１、２から把握される発明を示す。
（１）本発明の第１の態様に係るレーザ加速粒子ビーム装置は、レーザ光によって標的を励起することによって、粒子ビームを発生させるレーザ加速粒子ビーム装置であって、レーザ光の一部を通過させる開口を有する開口マスクと、前記開口マスクの開口を通過したレーザ光を反射して、前記標的内に設定された焦点に収束させる凹面鏡と、を備え、前記開口マスクは、前記開口マスクを通過するレーザ光を横切る方向に可動である。これにより、レーザ光を横切る方向に開口マスクを動かすことで、レーザ光の収束点（焦点）を実質的に動かすことなく、焦点に収束するレーザ光の入射方向を調節できる。 (Inventions Grasp from Above Embodiments 1 and 2)
Inventions understood from the first and second embodiments are described below.
(1) A laser-accelerated particle beam device according to a first aspect of the present invention is a laser-accelerated particle beam device that generates a particle beam by exciting a target with laser light. and a concave mirror that reflects laser light that has passed through the aperture of the aperture mask and converges it to a focal point set within the target, the aperture mask passing through the aperture mask. It is movable in a direction transverse to the laser beam. Accordingly, by moving the aperture mask in a direction across the laser light, the incident direction of the laser light converging on the focal point can be adjusted without substantially moving the convergence point (focus) of the laser light.
（２）本発明の第２の態様に係るレーザ加速粒子ビーム装置は、前記開口マスクを通過するレーザ光を横切る方向に、前記開口マスクを移動させる移動機構を備える。これにより、移動機構によって、開口マスクを移動できる。 (2) A laser-accelerated particle beam apparatus according to a second aspect of the present invention comprises a moving mechanism for moving the aperture mask in a direction transverse to laser light passing through the aperture mask. Thereby, the opening mask can be moved by the moving mechanism.
（３）本発明の第３の態様に係るレーザ加速粒子ビーム装置において、前記開口マスクの開口の内側面は、前記開口マスクを通過するレーザ光の回折を低減するための凹凸を有する。これにより、開口マスクの開口の内側面の凹凸によって、開口でのレーザ光の回折に起因する光学素子等の損傷を低減できる。 (3) In the laser accelerated particle beam apparatus according to the third aspect of the present invention, the inner surface of the aperture of the aperture mask has irregularities for reducing diffraction of laser light passing through the aperture mask. As a result, it is possible to reduce damage to optical elements and the like due to diffraction of laser light at the openings due to unevenness on the inner side surfaces of the openings of the opening mask.
（４）本発明の第４の態様に係るレーザ加速粒子ビーム装置において、前記開口の内側面は、前記開口の中心部に向かって突出する複数の凸部を有する。これにより、開口の中心部に向かって突出する複数の凸部によって、開口でのレーザ光の回折に起因する光学素子等の損傷を低減できる。 (4) In the laser accelerated particle beam device according to the fourth aspect of the present invention, the inner surface of the opening has a plurality of projections projecting toward the center of the opening. As a result, the plurality of projections protruding toward the center of the aperture can reduce damage to optical elements and the like due to diffraction of laser light at the aperture.
（５）本発明の第５の態様に係るレーザ加速粒子ビーム装置において、前記開口の概形は、円形または楕円形状である。開口の概形を、円形または楕円形状とすることで、開口でのレーザ光の回折に起因する光学素子等の損傷を低減できる。 (5) In the laser accelerated particle beam device according to the fifth aspect of the present invention, the general shape of the opening is circular or elliptical. By making the approximate shape of the aperture circular or elliptical, it is possible to reduce damage to optical elements and the like due to diffraction of laser light at the aperture.
（６）本発明の第６の態様に係るレーザ加速粒子ビーム装置において、前記凹面鏡は、軸外し放物面鏡である。凹面鏡の光軸外からのレーザ光を焦点に収束できる。 (6) In the laser accelerated particle beam device according to the sixth aspect of the present invention, the concave mirror is an off-axis parabolic mirror. Laser light from outside the optical axis of the concave mirror can be converged to the focal point.
（７）本発明の第７の態様に係るレーザ加速粒子ビーム装置において、前記粒子は、電子またはイオンである。これにより、レーザ光を用いて、電子またはイオンを加速できる。 (7) In the laser accelerated particle beam device according to the seventh aspect of the present invention, the particles are electrons or ions. Thereby, electrons or ions can be accelerated using laser light.
（８）本発明の第７の態様に係るレーザ加速粒子ビーム発生方法はレーザ光が開口マスクの開口を通過する工程と、凹面鏡が前記開口を通過したレーザ光を反射して、標的内に設定された焦点に収束させる工程と、前記焦点に収束されるレーザ光が、前記標的を励起して、粒子ビームを発生させる工程と、前記開口マスクが、前記開口を通過するレーザ光を横切る方向に移動する工程と、前記開口マスクの移動に対応して、前記凹面鏡によって収束されるレーザ光の前記焦点への入射角度が変化する工程と、前記入射角度の変化に応じて、前記標的からの粒子ビームの出射方向が変化する工程と、を有する。これにより、レーザ光を横切る方向に開口マスクを動かすことで、レーザ光の収束点（焦点）を実質的に動かすことなく、焦点に収束するレーザ光の入射方向を変化させて、粒子ビームの出射方向を調節できる。 (8) A method for generating a laser-accelerated particle beam according to the seventh aspect of the present invention includes the step of passing a laser beam through an aperture of an aperture mask; laser light focused to the focal point excites the target to generate a particle beam; and the aperture mask traverses the laser light passing through the aperture. changing the angle of incidence of the laser light converged by the concave mirror on the focal point corresponding to the movement of the aperture mask; and changing the direction of beam emission. As a result, by moving the aperture mask in the direction across the laser light, the incident direction of the laser light converging on the focal point can be changed without substantially moving the convergence point (focus) of the laser light, thereby emitting the particle beam. You can adjust the direction.
　本発明は上述した各実施形態に限定されるものではなく、請求項に示した範囲で種々の変更が可能であり、異なる実施形態にそれぞれ開示された技術的手段を適宜組み合わせて得られる実施形態についても本発明の技術的範囲に含まれる。 The present invention is not limited to the above-described embodiments, but can be modified in various ways within the scope of the claims, and can be obtained by appropriately combining technical means disclosed in different embodiments. is also included in the technical scope of the present invention.
１０　粒子ビーム装置
１１　レーザ光源
１２　開口マスク
１３　移動機構
１４　凹面鏡
１５　標的
１６ａ、１６ｂ　蛍光板
１７ａ、１７ｂ、１７ｃ　撮像器
１８　偏向磁石
１９　開口部 10 Particle Beam Device 11 Laser Light Source 12 Aperture Mask 13 Moving Mechanism 14 Concave Mirror 15 Targets 16a, 16b Fluorescent Screens 17a, 17b, 17c Imager 18 Bending Magnet 19 Aperture

Claims (8)

  1. 　レーザ光によって標的を励起することによって、粒子ビームを発生させるレーザ加速粒子ビーム装置であって、
    　レーザ光の一部を通過させる開口を有する開口マスクと、
    　前記開口マスクの開口を通過したレーザ光を反射して、前記標的内に設定された焦点に収束させる凹面鏡と、
    　を備え、
    　前記開口マスクは、前記開口マスクを通過するレーザ光を横切る方向に可動である、レーザ加速粒子ビーム装置。     A laser accelerated particle beam device for generating a particle beam by exciting a target with laser light,
    an aperture mask having an aperture that allows a portion of the laser light to pass;
    a concave mirror that reflects the laser light that has passed through the aperture of the aperture mask and converges it to a focal point set within the target;
    with
    A laser accelerated particle beam device, wherein the aperture mask is movable in a direction transverse to the laser light passing through the aperture mask.
  2. 　前記開口マスクを通過するレーザ光を横切る方向に、前記開口マスクを移動させる移動機構を備える、請求項１に記載のレーザ加速粒子ビーム装置。 The laser accelerated particle beam apparatus according to claim 1, comprising a moving mechanism for moving the aperture mask in a direction that traverses the laser light passing through the aperture mask.
  3. 　前記開口マスクの開口の内側面は、前記開口を通過するレーザ光の回折を低減するための凹凸を有する、請求項１または２に記載のレーザ加速粒子ビーム装置。 The laser accelerated particle beam apparatus according to claim 1 or 2, wherein the inner side surface of the aperture of said aperture mask has unevenness for reducing diffraction of laser light passing through said aperture.
  4. 　前記開口の内側面は、前記開口の中心部に向かって突出する複数の凸部を有する、請求項３に記載のレーザ加速粒子ビーム装置。 The laser-accelerated particle beam apparatus according to claim 3, wherein the inner surface of said opening has a plurality of projections projecting toward the center of said opening.
  5. 　前記開口の概形は、円形または楕円形状である、請求項１から４のいずれか1項に記載のレーザ加速粒子ビーム装置。 The laser accelerated particle beam device according to any one of claims 1 to 4, wherein the general shape of said aperture is circular or elliptical.
  6. 　前記凹面鏡は、軸外し放物面鏡である、請求項１から５のいずれか1項に記載のレーザ加速粒子ビーム装置。 The laser accelerated particle beam device according to any one of claims 1 to 5, wherein the concave mirror is an off-axis parabolic mirror.
  7. 　前記粒子は、電子またはイオンである、請求項１から６のいずれか1項に記載のレーザ加速粒子ビーム装置。 The laser accelerated particle beam device according to any one of claims 1 to 6, wherein the particles are electrons or ions.
  8. 　レーザ光が開口マスクの開口を通過する工程と、
    　凹面鏡が前記開口を通過したレーザ光を反射して、標的内に設定された焦点に収束させる工程と、
    　前記焦点に収束されるレーザ光が、前記標的を励起して、粒子ビームを発生させる工程と、
    　前記開口マスクが、前記開口を通過するレーザ光を横切る方向に移動する工程と、
    　前記開口マスクの移動に対応して、前記凹面鏡によって収束されるレーザ光の前記焦点への入射角度が変化する工程と、
    　前記入射角度の変化に応じて、前記標的からの粒子ビームの出射方向が変化する工程と、
    　を有する、レーザ加速粒子ビーム発生方法。     passing the laser light through the apertures of the aperture mask;
    a concave mirror reflecting the laser light passing through the aperture to a focal point set within the target;
    the focused laser light excites the target to generate a particle beam;
    moving the aperture mask in a direction transverse to laser light passing through the apertures;
    a step of changing the incident angle of the laser light converged by the concave mirror to the focal point in accordance with the movement of the aperture mask;
    changing the exit direction of the particle beam from the target according to the change in the incident angle;
    A method for generating a laser accelerated particle beam, comprising:
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