CN105700157A - Spectral dispersion smoothing method based on composite grating in inertial confinement fusion device - Google Patents

Spectral dispersion smoothing method based on composite grating in inertial confinement fusion device Download PDF

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CN105700157A
CN105700157A CN201610254958.2A CN201610254958A CN105700157A CN 105700157 A CN105700157 A CN 105700157A CN 201610254958 A CN201610254958 A CN 201610254958A CN 105700157 A CN105700157 A CN 105700157A
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smoothing
dispersion
grating
spectral dispersion
laser beam
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CN105700157B (en
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张彬
侯鹏程
钟哲强
王健
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Sichuan University
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Sichuan University
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0927—Systems for changing the beam intensity distribution, e.g. Gaussian to top-hat
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0938—Using specific optical elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0938—Using specific optical elements
    • G02B27/0944—Diffractive optical elements, e.g. gratings, holograms

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  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
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  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

The invention relates to a spectral dispersion smoothing method based on a composite grating in an inertial confinement fusion device and a smoothing device thereof. According to the method, the spectral dispersion smoothing device based on the composite grating is additionally arranged in an inertial confinement fusion device optical transmission line pre-amplification system or main amplification system; the spectral dispersion smoothing device is composed of a phase modulator and the composite grating; the phase modulator is used for performing time phase modulation on laser beams so that the bandwidth required by spectral angular dispersion of the composite grating is enabled to be generated; and the composite grating is used for controlling the dispersion direction of the laser beams. Regional spectral dispersion is performed on the laser beams to realize far-field speckle multi-direction sweeping of the laser beams so that omnibearing smoothing of the laser beams can be realized at a far-field focus within a short integral period of time, i.e. uniformity of the laser beams for target irradiation can be improved. Compared with existing special gratings, the composite grating is low in processing difficulty, relatively simple in structure and easier for large-aperture processing.

Description

Based on the smoothing by spectral dispersion method of compound grating in inertially confinement fusion device
Technical field
The present invention relates to beam smoothing technology in a kind of Laser Driven inertially confinement fusion device, be specifically related in a kind of Laser Driven inertial confinement fusion (ICF) device based on the smoothing by spectral dispersion method of compound grating and even sliding device thereof。
Background technology
In Laser Driven inertial confinement fusion (ICF) device, owing to Physical Experiment requires that device of high power laser accurate can control target surface optical field distribution, thus it is widely used various spatial domains beam smoothing technology and time domain beam smoothing technology, to realize the control to laser beam far-field focus uniformity in ICF device, that is improve its uniformity to target surface irradiation。In the beam smoothing technology of existing spatial domain, frequently with continuous phase plate (ContinuousPhasePlate, CPP) control laser beam far-field focus profile, but due to the coherent superposition between the internal beamlet of laser beam, inside its far-field focus, there is pattern；This class pattern can cause laser beam and the generation of various parametric instability effects in pellet interaction process, thus reducing the laser beam compression symmetry to pellet, so that adopt time domain beam smoothing technology to suppress the existence of speckle, reduce the harm of various parametric instability effect。Existing time domain beam smoothing technology mainly includes the technology such as polarization smoothing and the spectral modeling even cunning of dispersion。
Described polarization smoothing technology is to utilize birefringent wedge, polarization to rotate the optical element such as to pull and change the polarization state in beam cross section, it is achieved the eliminating coherence superposition of the internal beamlet of light beam, to reduce far-field focus contrast。The advantage of this method is the instantaneous even cunning realizing focal spot of energy, far-field focus uniformity for improving the target surface irradiation initial stage is fruitful, but birefringent wedge is mainly used in the even cunning of single light beam, and the damage that stimulated Raman scattering brings can be subject to, polarize that to rotate the shortcoming pulled be then only just have even sliding effect when multiple beam superposition。
Described spectral modeling dispersion (SmoothingbySpectralDispersion, SSD) even sliding technology is by laser beam carrying out Temporal modulation and utilizing grating to carry out spectral modeling dispersion, realize the sweeping of laser beam speckle, thus improving far-field focus uniformity within the plasma heat even sliding time。At present, the shortcoming of one-dimensional SSD (1D-SSD) is to be only capable of realizing laser beam far field speckle in grating dispersion direction, the i.e. sweeping in x direction or y direction, cause the internal intensity modulation that the striated along grating dispersion direction occurs of its far-field focus, thus also been proposed the two dimension even sliding technology of SSD, it is simultaneously achieved the laser beam beam smoothing at two orthogonal directions in x direction and y direction；But owing to laser beam exists inevitable coherent phenomena in far field in two dimension SSD, proposing the three even sliding technology of direction SSD in turn, this even sliding technology, by making the frequency of near field laser beam tend to random, further increases target surface irradiation uniformity。But, there is light channel structure complexity, regulate the shortcomings such as difficulty in the three even sliding technology of direction SSD。
In order to make up the deficiency of striated pattern list dispersion direction, it is proposed that Circular gratings, spiral grating and array grating。Wish the dispersion mode by special Circular gratings, spiral grating and array grating, obtain beam smoothing effect more preferably。Circular gratings focal spot diametrically has obvious even sliding effect, namely the diffraction fringe around circumference groove is had good inhibition。Weak point is, owing to not having spectral modeling dispersion at circumferencial direction, diffraction fringe exists in a large number。The dispersion direction of spiral grating is at circumferencial direction, owing to the closer to circle center, grating line is more close, thus increases difficulty of processing。But locating away from circle center, the dispersion measure caused due to grating is less, for obtaining suitable chromatic dispersion effects, need to increase total groove of grating, and this will be further increased difficulty of processing。Array grating introduces multiple dispersion direction, but theoretical research shows, raster unit number increase the even sliding effect that can't improve focal spot further, simultaneously unit number increase the difficulty of processing that can increase reality。
Summary of the invention
The purpose of the present invention is precisely in order to overcome defect existing in prior art and deficiency, it is provided that based on the smoothing by spectral dispersion new method of compound grating in a kind of inertially confinement fusion device, and realize the smoothing by spectral dispersion device of the method。The method is in inertially confinement fusion device optical transport chain, addition one is based on the smoothing by spectral dispersion device of compound grating, laser beam far-field focus even cunning in different directions can be realized, thus improving the uniformity of laser beam remote irradiation within the shorter time of integration, namely improve its uniformity to target surface irradiation。
The inertially confinement fusion device that the present invention proposes can be used for directly driving and indirectly driving in inertially confinement fusion device based on the smoothing by spectral dispersion method of compound grating and even sliding device, to improve the uniformity to target surface irradiation。
For achieving the above object, the present invention adopts the technical scheme being made up of techniques below measure to realize。
The design concept of the present invention is: in the preamplifier system in Laser Driven inertially confinement fusion device optical transport chain or after main amplification system, addition one is based on the smoothing by spectral dispersion device of compound grating, first laser beam is carried out Temporal modulation, for laser beam characteristic, again laser beam is carried out region spectral dispersion, to realize the multi-direction sweeping of laser beam far field speckle, thus making the far-field focus of laser beam realize comprehensive even cunning within the shorter time of integration, namely improve the laser beam uniformity to target surface irradiation。
The described smoothing by spectral dispersion device based on compound grating is made up of phase-modulator and compound grating；Wherein phase-modulator is used for laser beam is produced Temporal modulation, in order to produces compound grating and carries out the bandwidth required for spectral modeling dispersion；Compound grating is used for controlling the dispersion direction of laser beam。In order to ensure the even sliding effect of compound grating and reduce the difficulty of processing of compound grating, the compound grating adopted is plane transmission grating。Simultaneously in order to ensure the symmetry transmission of laser beam after dispersion, the central shaft of described compound grating and the central shaft conllinear of incoming laser beam, and the dispersion area of compound grating is divided into two parts: with the central axial outer border circular areas of compound grating for dispersion area i, its radius is a certain fixed value, dispersion is dispersion mode I, this dispersion mode can be one-dimensional dispersion or footpath crossed disperstion, and the region beyond border circular areas is dispersion area ii, its dispersion is dispersion mode II, and this dispersion mode is circumferencial direction dispersion or footpath crossed disperstion。In described optical transport chain, the laser beam of seed light output unit output sequentially passes through preamplifier system, phase-modulator, compound grating, main amplification system, frequency translation unit and continuous phase plate (CPP), and last line focus lens focus is to target surface；By the laser beam of phase modulator modulation through compound grating, the laser beam being in border circular areas carries out dispersion according to dispersion mode I, is in the laser beam beyond border circular areas and carries out dispersion according to dispersion mode II。When two-part dispersion area is chosen rational dispersion area and dispersion mode, the speckle within far-field focus can be made in multi-direction quick sweeping, thus floating focal spot is at the modulated structure of dispersion direction within the short time of integration, to improve the laser beam uniformity to target surface irradiation。
Based on the smoothing by spectral dispersion method of compound grating in a kind of inertially confinement fusion device provided by the invention, comprise the following steps:
(1) in Laser Driven inertially confinement fusion device optical transport chain, add a smoothing by spectral dispersion device, and regulate the modulating frequency ω of phase-modulator in this devicemParameter value；
(2) with the phase-modulator described in step (1), incoming laser beam in optical transport chain is carried out Temporal modulation；
(3) incoming laser beam in optical transport chain after phase modulated device modulation described in step (2), again through the compound grating in smoothing by spectral dispersion device；
(4) described in step (3), incoming laser beam passes through compound grating, the chromatic dispersion region of compound grating is divided into dispersion area i and dispersion area ii two parts,, laser beam carries out the spectral dispersion of different directions respectively simultaneously through the dispersion area i and dispersion area ii of compound grating；
(5) in optical transport chain described in step (4), laser beam, after spectral dispersion, sequentially passes through beam expander in inertially confinement fusion device, main amplification system, continuous phase plate, and last line focus lens focus is to target surface；The far-field focus of laser beam is carrying out the spectral dispersion of different directions through compound grating, causes the internal speckle of far-field focus in the quick sweeping of respective dispersion direction, it is achieved even cunning to target surface within the short time of integration, namely improves the uniformity of target surface irradiation。
In technique scheme, the smoothing by spectral dispersion device added described in step (1), is among the preamplifier system in inertially confinement fusion device optical transport chain, or adds smoothing by spectral dispersion device after main amplification system。
In technique scheme, the smoothing by spectral dispersion device added described in step (1) is made up of phase-modulator and compound grating。
In technique scheme, in described smoothing by spectral dispersion device, the external diameter of compound grating is identical with incoming laser beam bore。
Described in step of the present invention (2), laser beam is through phase modulator modulation with after obtaining spectrum widening, and the electric field intensity of laser beam is represented by:
E in formula0For initial laser beam light field, ω0For the angular frequency of initial laser beam, δ and ωmRespectively modulation depth and modulating frequency。
Laser beam in optical transport chain described in step of the present invention (3) carries out the expression formula after spectral dispersion by compound grating:
Wherein,
R s 1 ( x , y ) = 1 , ( x 2 + y 2 ≤ r 2 ) 0 , ( x 2 + y 2 ≥ r 2 ) - - - ( 3 )
R s 2 ( x , y ) = 1 , ( x 2 + y 2 ≥ r 2 ) 0 , ( x 2 + y 2 ≤ r 2 ) - - - ( 4 )
In formula, r is the radius of circular dispersion area i,For the abbe number of compound grating border circular areas i,Dispersion direction for compound grating circle dispersion area i；For the abbe number of compound grating dispersion region ii,For the dispersion direction of compound grating dispersion region ii, and
When compound grating border circular areas i adopts one-dimensional linear dispersion,
When dissipating when compound grating border circular areas i adopts radially color,
When compound grating region ii adopts circumferencial direction dispersion,
When compound grating region ii adopts footpath crossed disperstion,
In the formula of (5)～(8), it is common to use circle groove realizes footpath crossed disperstion, uses star-like ruling grating to realize circumferencial direction dispersion。
In time of integration described above Δ t, far-field intensity distribution is:
In formula, Δ t is the time of integration,It is distributed for laser beam Near-field optical field,For the additive phase of continuous phase plate (CPP), " FT " represents Fourier transformation, and " | | " represents and take absolute value。
The even sliding device of the smoothing by spectral dispersion method realized in described inertially confinement fusion device based on compound grating provided by the invention, including seed light output unit, preamplifier system, lens, beam expander, main amplification system, frequency translation unit, continuous phase plate, condenser lens, target surface；According to the present invention, also including smoothing by spectral dispersion device, described smoothing by spectral dispersion device is made up of phase-modulator and compound grating；Describe according to light path: in described optical transport chain, after sequentially passing through preamplifier system, phase-modulator, compound grating, main amplification system, frequency translation unit, continuous phase plate from the laser beam of seed light output unit output, last line focus lens focus is to target surface；The far-field focus of laser beam is carrying out the dispersion of different directions through compound grating, cause the internal speckle of far-field focus in the quick sweeping of respective dispersion direction, realize the even cunning to target surface within the shorter time of integration, namely improve the laser beam uniformity to target surface irradiation。
In technique scheme, described smoothing by spectral dispersion device is arranged among the preamplifier system of optical transport chain or after main amplification system。
In technique scheme, the phase-modulator in described smoothing by spectral dispersion device is electrooptic modulator, to realize the sinusoidal phase modulation of laser beam in optical transport chain。
In technique scheme, in described smoothing by spectral dispersion device, the external diameter of compound grating is identical with incoming laser beam bore。
In technique scheme, the compound grating in described smoothing by spectral dispersion device adopts plane transmission grating。
In technique scheme, in described smoothing by spectral dispersion device, compound grating is processed by the plane transmission grating of high damage threshold。
Based on the smoothing by spectral dispersion method of compound grating and even sliding device in inertially confinement fusion device of the present invention, inertially confinement fusion device optical transport chain use under the premise of continuous phase plate, described smoothing by spectral dispersion device can be placed in the big system of prevention, or after main amplification system, thus causing the internal speckle of laser beam focal spot in optical transport chain quickly to sweep along different directions at different dispersion areas, to realize the far field speckle of laser beam in optical transport chain in the even cunning in compound grating dispersion direction simultaneously。
The present invention compared with prior art have the advantage that and useful technique effect are as follows:
1, present invention firstly provides the smoothing by spectral dispersion method based on compound grating in the Laser Driven system of inertially confinement fusion device, and a kind of smoothing by spectral dispersion device realizing the method is provided, it is achieved that in optical transport chain, laser beam speckle is at the beam smoothing in compound grating dispersion direction。It is different from the dispersion of traditional array type grating that described smoothing by spectral dispersion device utilizes compound grating to carry out subregion dispersion, and traditional array type raster unit number is more, and dispersion area dividing mode also has difference；If Circular gratings dispersion direction is that radially spiral grating dispersion direction is circumferencial direction, and dispersion direction is all comparatively single。
2, based on the smoothing by spectral dispersion method of compound grating and even sliding device in inertially confinement fusion device of the present invention, compared with existing 1D-SSD, owing to dispersion mode increases, the generation that laser beam produces the intensity modulated of striated in far field can effectively be reduced；Compared with 2D-SSD, the laser beam through compound grating dispersion can be prevented effectively from the coherent phenomena in far field。
3, based on the smoothing by spectral dispersion method of compound grating and even sliding device in inertially confinement fusion device of the present invention, it is utilize compound grating that laser beam is carried out subregion dispersion, owing to using circumferencial direction dispersion at dispersion area ii, when grating compound in smoothing by spectral dispersion device is positioned in preamplifier system, the via efficiency reducing spatial filter owing to the focal spot size of grating dispersion introducing becomes big can be prevented effectively from；Time after grating compound in smoothing by spectral dispersion device is positioned over main amplification system, the focal spot size introduced due to grating dispersion can be prevented effectively from and become big and cause the plug-hole problem at hand-hole place, fusion black chamber。
4, based on the smoothing by spectral dispersion method of compound grating and even sliding device in inertially confinement fusion device of the present invention, in this smoothing by spectral dispersion device, compound grating is with existing special grating such as: compared with Circular gratings, spiral grating, array grating etc., it is less at the incisure density of dispersion area i, thus difficulty of processing is less, structure is relatively easy and is easier to heavy caliber processing。
Accompanying drawing explanation
Fig. 1 is the structural representation that the embodiment of the present invention 1 realizes that the even sliding device of the smoothing by spectral dispersion method in described inertially confinement fusion device based on compound grating is placed in preamplifier system；
Fig. 2 is that the embodiment of the present invention 2 realizes the even sliding device of the smoothing by spectral dispersion method in described inertially confinement fusion device based on compound grating and is placed in the structural representation after main amplification system；
Fig. 3 is based on the structural representation of compound grating in the even sliding device of the smoothing by spectral dispersion method of compound grating in inertially confinement fusion device of the present invention；
Fig. 4 is that wherein, (a) is the focal spot of compound grating light beam based on focal spot when having continuous phase plate in the smoothing by spectral dispersion method of compound grating in inertially confinement fusion device of the present invention；B () is the focal spot of existing 1D-SSD light beam；C () is the focal spot of existing spiral grating light beam；
Fig. 5 is the dispersion direction schematic diagram of the smoothing by spectral dispersion method in inertially confinement fusion device of the present invention based on compound grating, and wherein, (a) is compound grating beam smoothing direction；B () is existing 1D-SSD beam smoothing direction；C () is existing spiral grating beam smoothing direction；
Fig. 6 is based on when having continuous phase plate in the smoothing by spectral dispersion method of compound grating in inertially confinement fusion device of the present invention, compound grating, 1D-SSD, spiral grating three kinds of beam smoothing schemes under, the FOPAI curve of its focal spot；
Fig. 7 is based on when having continuous phase plate in the even sliding method of compound grating spectrum dispersion in inertially confinement fusion device of the present invention, compound grating, 1D-SSD, spiral grating three kinds of beam smoothing schemes under, luminous flux contrast C ontrast is with the change curve of the Δ t time of integration。
In Fig. 1,1 seed light output unit, 2 preamplifier systems, 3 lens, 4 phase-modulators, 5 compound gratings, 6 beam expanders, 7 main amplification systems, 8 frequency translation units, 9 continuous phase plates, 10 condenser lenses, 11 target surfaces, 12 smoothing by spectral dispersion devices。
Detailed description of the invention
Below in conjunction with accompanying drawing and with specific embodiment, the present invention is described in further detail, it is necessary to it is pointed out here that the embodiment being described be only intended to further describing the present invention, and be not meant to be any restriction to scope。
Based on the smoothing by spectral dispersion method of compound grating in inertially confinement fusion device of the present invention, and the structure that the smoothing by spectral dispersion device realizing the method provided is placed in preamplifier system is as shown in Figure 1。Including seed light output unit 1, preamplifier system 2, lens 3, beam expander 6, main amplification system 7, frequency translation unit 8, continuous phase plate 9, condenser lens 10, target surface 11；Also including smoothing by spectral dispersion device 12, described smoothing by spectral dispersion device 12 is made up of phase-modulator 4 and compound grating 5。Describe by light path: the laser beam of described seed light output unit 1 output sequentially passes through preamplifier system 2, lens 3, phase-modulator 4 and compound grating 5 in smoothing by spectral dispersion device 12, beam expander 6, main amplification system 7, frequency translation unit 8, continuous phase plate 9, condenser lens 10, finally arrive target surface 11；Further as shown in Figure 1, in described optical transport chain, laser beam is after phase-modulator 4 carries out Temporal modulation, by compound grating 5, now laser beam carries out the dispersion of different directions respectively simultaneously through the dispersion area i and dispersion area ii of compound grating 5；Laser beam, after spectral dispersion, sequentially passes through main amplification system 7, frequency translation unit 8, continuous phase plate 9, and last line focus lens 10 focus on target surface 11；The far-field focus of laser beam is carrying out the dispersion of different directions through compound grating 5, causes the internal speckle of far-field focus in the quick sweeping of respective dispersion direction, it is achieved even cunning to target surface 11 within the shorter time of integration, namely improves the uniformity of target surface irradiation。
The present invention is in order to ensure the symmetry transmission of laser beam after dispersion, the central shaft of described compound grating 5 and the central shaft conllinear of incoming laser beam, the dispersion area of compound grating 5 is divided into two parts by incoming laser beam: be namely divided into dispersion area i with the central axial outer circular dispersion area of compound grating 5, its dispersion is dispersion mode I, dispersion mode I can be one-dimensional dispersion or footpath crossed disperstion, and described circular dispersion area radius is the region of a certain fixed value；And the dispersion area beyond circle dispersion area is divided into dispersion area ii, its dispersion is dispersion mode II, and dispersion mode II can be circumferencial direction dispersion or footpath crossed disperstion。
In Fig. 2 of the present invention, it is achieved in described inertially confinement fusion device, the smoothing by spectral dispersion device of smoothing by spectral dispersion method based on compound grating is placed in the structure after main amplification system as shown in Figure 2。Describe by light path: the laser beam of described seed light output unit 1 output sequentially passes through preamplifier system 2, lens 3, beam expander 6, main amplification system 7, frequency translation unit 8, phase-modulator 4 and compound grating 5 in smoothing by spectral dispersion device 12, continuous phase plate 9, condenser lens 10, finally arrive target surface 11；Further as shown in Figure 2, in described optical transport chain after laser beam elapsed time phase-modulation, by compound grating 5, now laser beam carries out the dispersion of different directions respectively simultaneously through the dispersion area i and dispersion area ii of compound grating 5；Laser beam is after spectral dispersion, and then through continuous phase plate 9, last line focus lens 10 focus on target surface 11；The far-field focus of laser beam is carrying out the dispersion of different directions through compound grating 5, cause the internal speckle of far-field focus in the quick sweeping of respective dispersion direction, realize the even cunning to target surface 11 within the shorter time of integration equally, namely improve the uniformity of target surface irradiation。
In Fig. 3 of the present invention, the dispersion area i at center is the central axial outer circular dispersion area with compound grating 5；The dispersion area ii of outside is the dispersion area beyond circular dispersion area。
In Fig. 4 of the present invention, described based on focal spot when having continuous phase plate in the smoothing by spectral dispersion method of compound grating, it is seen that the focal spot of (a) compound grating light beam, it does not have significantly diffraction fringe；, there is diffraction fringe in groove direction in the focal spot of (b) existing 1D-SSD light beam；, radially there is diffraction fringe in the focal spot of (c) existing spiral grating light beam。
In Fig. 5 of the present invention, the dispersion of compound grating is divided into both direction, dispersion area i to be one-dimensional linear dispersion, and dispersion area ii is circumferencial direction dispersion；Existing 1D-SSD is one-dimensional linear dispersion；Existing spiral grating is radial direction dispersion。
Embodiment 1
In the present embodiment employing inertially confinement fusion device as shown in Figure 1, the even sliding device based on the smoothing by spectral dispersion method of compound grating is placed in the structural representation in preamplifier system 2。
In the present embodiment, the phase-modulator 4 in smoothing by spectral dispersion device used is electrooptic modulator, and described the put position of compound grating is in preamplifier system；The dispersion direction of the dispersion area i of compound grating 5 used is one-dimensional x orientational dispersion, and its abbe number isThe dispersion area ii of compound grating is circumferencial direction dispersion, the total groove M=20000 of its grating, and the dispersion area of composite grating dispersion area i and dispersion area ii is identical, the time of integration Δ t=10ps。
Described incoming laser beam bore is 30mm, and the external diameter of compound grating 5 used is identical with laser beam bore。
The described concrete operation step based on the smoothing by spectral dispersion method of compound grating is as follows:
(1) in Laser Driven inertially confinement fusion device optical transport chain preamplifier system 2, add a smoothing by spectral dispersion device, and regulate the parameter value of Temporal modulation device 4, wherein modulating frequency ω in this devicem=17GHZ and modulation depth δ=2.38；
(2) with step (1) described phase-modulator 4, laser beam in optical transport chain is carried out sinusoidal time phase-modulation；
(3) in optical transport chain described in step (2), incoming laser beam is after phase-modulator 4 is modulated, and again through compound grating 5, this compound grating external diameter is identical with incoming laser beam bore 30mm；
(4) described in step (3), incoming laser beam passes through compound light 5, the dispersion area of compound grating 5 is divided into dispersion area i and dispersion area ii two parts, and it carries out the dispersion of different directions respectively simultaneously through the dispersion area i and dispersion area ii of compound grating 5；Dispersion area i is one-dimensional x orientational dispersion, and its abbe number isDispersion area ii is circumferencial direction dispersion, the total groove M=20000 of its grating；
(5) in optical transport chain described in step (4), incoming laser beam, after spectral dispersion, sequentially passes through beam expander 6, main amplification system 7, frequency translation unit 8, continuous phase plate 9, and last line focus lens 10 focus on target surface 11；The far-field focus of laser beam is carrying out the dispersion of different directions through compound grating 5, cause the internal speckle of far-field focus in the quick sweeping of respective dispersion direction, realize the even cunning to target surface 11 within the shorter time of integration, namely improve the uniformity of target surface 11 irradiation。
For convenience of comparison, the smoothing by spectral dispersion method of embodiment 1 is compared with typical one-dimensional 1D-SSD and spiral grating, wherein the parameter of 1D-SSD is according to document (S.Skupsky, R.W.Short, T.Kessler, etal..Improvedlaserbeamuniformityusingtheangulardispersi onoffrequencymodulatedlight.J.Appl.Phys.66,3456 (1989) .) choose, i.e. the modulating frequency ω of Temporal Phase Modulationm=2.5GHz, modulation depth is δ=12, and grating dispersion coefficient isWherein the parameter of spiral grating is according to document (RuiZhang, XiaominZhang, ZhanSui, andHaiMing.Researchontargetuniformirradiationmethodusing linearlymodulatedlightandspecialgratingdispersion.Optics &LaserTechnology, 43:1073-1077) choose。
The improvement effect of far-field focus uniformity has been shown by the smoothing by spectral dispersion method based on compound grating that Fig. 4～Fig. 7 is in embodiment 1, and from each figure, acquired results has absolutely proved the smoothing by spectral dispersion method based on compound grating of the present invention and the effectiveness of even sliding device, feasibility。
Shown in Fig. 4, when compared for continuous phase plate 9, radially even sliding method, 1D-SSD, radially even cunning and 1D-SSD are used in combination the focal spot distribution under three kinds of schemes。In Fig. 4, (a) is composite grating focal spot, does not have the intensity modulation of obvious striated inside focal spot, and focal spot size being not significantly changed；B () is existing 1D-SSD focal spot, focal spot obtains even cunning in y direction, there is the intensity modulation of obvious striated；C () is existing spiral grating focal spot, focal spot is radially having the intensity modulation of obvious striated。
Fig. 5 show the dispersion direction schematic diagram that radially even sliding method, 1D-SSD, the even cunning of radial direction and 1D-SSD are used in combination under three kinds of schemes。In Fig. 5, (a) is the even sliding direction of composite grating, and its dispersion is divided into both direction, dispersion area i to be one-dimensional linear dispersion, and dispersion area ii is circumferencial direction dispersion；B () is existing 1D-SSD beam smoothing direction, 1D-SSD is x orientational dispersion, and (c) is existing spiral grating beam smoothing direction, and its even sliding direction is footpath crossed disperstion。For the improvement degree of quantitative analysis focal spot uniformity, adopting focal spot luminous flux contrast (Contrast) to evaluate, focal spot luminous flux contrast is more little shows that focal spot uniformity is more good；Its formula is expressed as follows:
C o n t r a s t = Σ i Σ j [ I i , j ( x f , y f ) - I m e a n ] / N x N y I m e a n - - - ( 10 )
In formula, Ii,j(xf,yf) it is (xf,yf) light intensity of position；ImeanFor average intensity。
For the improvement degree of the internal hot spot of the even sliding technology focal spot of quantitative analysis bundle, adopting FractionalPoweraboveIntensity (FOPAI) curve to evaluate, FOPAI curve is more good to moving to left the improvement effect showing the internal hot spot of focal spot；Its formula is expressed as follows:
F O P A I = ∫ A w h e r e I ( x , y ) > I m e a n I ( x , y ) d x d y ∫ A I ( x , y ) d x d y - - - ( 11 )
In formula, A is focal spot area, ImeanFor average intensity
When the improvement degree of focal spot uniformity and internal hot spot carries out quantitative analysis, the region for 90% energy circle rate is calculated。
Utilize formula (10) and (11) that the light distribution of the focal spot shown in Fig. 4 calculates its light FOPAI respectively and flux vs writes music line, obtain shown in Fig. 6 and Fig. 7。
Shown in Fig. 6, when employing continuous phase plate 9, the FOPAI curve that the even sliding method of compound grating, 1D-SSD act on lower focal spot respectively with spiral grating is roughly the same, and the internal hot spot of focal spot is not significantly increased。
Shown in Fig. 7, when employing continuous phase plate 9, under the even sliding method of compound grating, 1D-SSD and spiral grating effect, the luminous flux contrast of focal spot is close, restraints even sliding effect suitable。
Displaying by above-described embodiment 1 and Fig. 4-Fig. 7, it was shown that the smoothing by spectral dispersion method based on compound grating in inertially confinement fusion device of the present invention and even sliding device can realize the effective even cunning of target surface in the shorter time of integration in 10ps。
Embodiment 2
The present embodiment adopts in inertially confinement fusion device as shown in Figure 2 and is placed in the structural representation after main amplification system 7 based on the even sliding device of the smoothing by spectral dispersion method of compound grating。
The dispersion direction of the dispersion area i of compound grating 5 used by this example is one-dimensional x orientational dispersion, and its abbe number isThe dispersion area ii of compound grating is footpath crossed disperstion, and its abbe number isThe dispersion area of composite grating dispersion area i and dispersion area ii is identical, the time of integration Δ t=10ps。
Described incoming laser beam bore is 360mm, and compound grating external diameter used is identical with this incoming laser beam bore。
Other operating process and step and embodiment 1 are identical, equally, in described optical transport chain, incoming laser beam is after phase-modulator 4 is modulated, and by compound grating 5, now laser beam carries out the dispersion of different directions respectively simultaneously through the dispersion area i and dispersion area ii of compound grating 5；Laser beam is after spectral dispersion, and through frequency translation unit 8, continuous phase plate 9, last line focus lens 10 focus on target surface 11；The far-field focus of laser beam is carrying out the dispersion of different directions through compound grating 5, causes the internal speckle of far-field focus in the quick sweeping of respective dispersion direction, it is achieved even cunning to target surface 11 within the shorter time of integration, namely improves the uniformity of target surface irradiation。
When compound grating dispersion region i adopts one-dimensional linear dispersion, and dispersion area ii adopts footpath crossed disperstion, the uniformity of target surface irradiation can be effectively improved equally。
Embodiment of the present invention only gives concrete example application, but for be engaged in inertial confinement fusion Laser Driven system in research worker for, also can designing multiple for the spectral dispersion beam smoothing structure based on compound grating in inertially confinement fusion device according to above enlightenment, this is still considered to be covered by among the present invention。

Claims (10)

1. based on the smoothing by spectral dispersion method of compound grating in an inertially confinement fusion device, it is characterised in that comprise the following steps:
(1) in the inertially confinement fusion device optical transport chain of Laser Driven, add a smoothing by spectral dispersion device (12), and regulate the modulating frequency ω of Temporal modulation device (4) in this devicemParameter value；
(2) with the Temporal modulation device (4) described in step (1), incoming laser beam in optical transport chain is carried out Temporal modulation；
(3) described in step (2) through Temporal modulation device (4) modulate after incoming laser beam, again through the compound grating (5) in smoothing by spectral dispersion device (12)；
(4) described in step (3), its dispersion area is divided into dispersion area i and dispersion area ii two parts by compound grating (5) by incoming laser beam, and laser beam carries out the dispersion of different directions respectively simultaneously through dispersion area i and dispersion area ii；
(5) described in step (4) laser beam after spectral dispersion, sequentially passing through beam expander in inertially confinement fusion device (6), main amplification system (7), frequency translation unit (8), continuous phase plate (9), last line focus lens (10) focus on target surface (11)；The far-field focus of laser beam is carrying out the spectral dispersion of different directions through compound grating (5), cause the internal speckle of far-field focus in the quick sweeping of respective dispersion direction, realize the even cunning to target surface within the short time of integration, namely improve the uniformity of target surface irradiation。
2. according to claim 1 based on the smoothing by spectral dispersion method of compound grating, it is characterized in that the smoothing by spectral dispersion device (12) added described in step (1), be add among the preamplifier system (2) in inertially confinement fusion device optical transport chain or after main amplification system (7)。
3. the smoothing by spectral dispersion method based on compound grating according to claim 1 or claim 2, it is characterised in that the smoothing by spectral dispersion device (12) added described in step (1) is made up of phase-modulator (4) and compound grating (5)。
4. according to claim 3 based on the smoothing by spectral dispersion method of compound grating, it is characterised in that in described smoothing by spectral dispersion device (12), the external diameter of compound grating (5) is identical with incoming laser beam bore。
5. the smoothing by spectral dispersion device of the smoothing by spectral dispersion method realized in inertially confinement fusion device described in any one of claim 1-4 based on compound grating, including seed light output unit (1), preamplifier system (2), lens (3), beam expander (6), main amplification system (7), frequency translation unit (8), continuous phase plate (9), condenser lens (10), target surface (11)；Characterized by further comprising smoothing by spectral dispersion device (12), this smoothing by spectral dispersion device is made up of phase-modulator (4) and compound grating (5)；Describe according to light path: in described optical transport chain, after the laser beam exported from seed light output unit (1) sequentially passes through preamplifier system (2), lens (3), phase-modulator (4), compound grating (5), beam expander (6), main amplification system (7), frequency translation unit (8) and continuous phase plate (9), last line focus lens (10) focus on target surface (11)；The far-field focus of laser beam is carrying out the dispersion of different directions through compound grating (5), cause the internal speckle of far-field focus in the quick sweeping of respective dispersion direction, realize the even cunning to target surface within the short time of integration, namely improve the laser beam uniformity to target surface irradiation。
6. according to claim 5 based on the smoothing by spectral dispersion device of compound grating, it is characterised in that described smoothing by spectral dispersion device (12) is arranged among the preamplifier system (2) of optical transport chain or after main amplification system (7)。
7. based on the smoothing by spectral dispersion device of compound grating according to claim 5 or 6, it is characterised in that the phase-modulator (4) in described smoothing by spectral dispersion device (12) is phase place electrooptic modulator。
8. based on the smoothing by spectral dispersion device of compound grating according to claim 5 or 6, it is characterised in that the compound grating (5) in described smoothing by spectral dispersion device (12) adopts plane transmission grating。
9. according to claim 8 based on the smoothing by spectral dispersion device of compound grating, it is characterised in that in described smoothing by spectral dispersion device (12), compound grating (5) is processed by the plane transmission grating of high damage threshold。
10. according to claim 5 based on the smoothing by spectral dispersion device of compound grating, it is characterised in that in described smoothing by spectral dispersion device (12), the external diameter of compound grating (5) is identical with incoming laser beam bore。
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