CN105700157B - Based on the smoothing by spectral dispersion method of compound grating in inertially confinement fusion device - Google Patents
Based on the smoothing by spectral dispersion method of compound grating in inertially confinement fusion device Download PDFInfo
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Abstract
The present invention relates in a kind of inertially confinement fusion device based on compound grating smoothing by spectral dispersion method and its even sliding device.This method is the one smoothing by spectral dispersion device based on compound grating of addition in inertially confinement fusion device optical transport chain preamplifier system or after main amplification system；The smoothing by spectral dispersion device is made of phase-modulator and compound grating；Wherein phase-modulator generates bandwidth needed for the compound grating carries out spectrum angle dispersion to make to laser beam generation time phase-modulation；Compound grating is used to control laser beam dispersion direction.The present invention carries out subregion spectral dispersion to laser beam, to realize the multi-direction sweeping of laser beam speckle, so that laser beam be made to realize comprehensive even cunning in far-field focus within the shorter time of integration, that is, improves the uniformity that laser beam irradiates target surface.For compound grating used in the present invention compared with existing special grating, difficulty of processing is smaller, and structure is relatively easy and is easier to heavy caliber processing.
Description
Technical field
The present invention relates to beam smoothing technologies in a kind of Laser Driven inertially confinement fusion device, and in particular to a kind of laser
Drive the smoothing by spectral dispersion method in inertial confinement fusion (ICF) device based on compound grating and its even sliding device.
Background technique
In Laser Driven inertial confinement fusion (ICF) device, since Physical Experiment requires device of high power laser can essence
Close control target surface optical field distribution, thus be widely used various airspace beam smoothing technologies and time domain beam smoothing technology, with
The control to laser beam far-field focus uniformity is realized in ICF device, that is, improves its uniformity to target surface irradiation.?
It is sharp to control frequently with continuous phase plate (Continuous Phase Plate, CPP) in existing airspace beam smoothing technology
Light far field beam focal spot profile, but due to the coherent superposition of sub-light interfascicular inside laser beam, far-field focus inside, which exists, to be dissipated
Spot structure；This kind of patterns will lead to the production of various parametric instability effects in laser beam and pellet interaction process
It is raw, to reduce laser beam to the compression symmetry of pellet, thus need to use time domain beam smoothing technology to inhibit speckle
In the presence of reducing the harm of various parametric instability effects.Existing time domain beam smoothing technology mainly include polarization smoothing and
The technologies such as the even cunning of spectrum angle dispersion.
The polarization smoothing technology is the optical elements such as to pull using birefringent wedge, polarization rotation to change in beam cross section
Polarization state realizes the eliminating coherence superposition of beamlet inside light beam, to reduce far-field focus contrast.The advantages of this method is energy
The instantaneous even cunning for realizing focal spot, it is fruitful for the far-field focus uniformity for improving target surface irradiation initial stage, but birefringent light
Wedge is mainly used for the even cunning of single light beam, and will receive the damage of stimulated Raman scattering bring, and polarizes the shortcomings that rotation is pulled
It is then only just to have even sliding effect when multiple beam superposition.
The even sliding technology of the spectrum angle dispersion (Smoothing by Spectral Dispersion, SSD) is by right
Laser beam carries out Temporal modulation and carries out spectrum angle dispersion using grating, realizes the sweeping of laser beam speckle, from
And far-field focus uniformity is improved within the plasma heat even sliding time.Currently, the shortcomings that one-dimensional SSD (1D-SSD) is to be only capable of reality
Existing laser beam far field speckle causes to occur inside its far-field focus in grating dispersion direction, the i.e. sweeping in the direction x or the direction y
Along the intensity modulation of the striated in grating dispersion direction, thus the even sliding technology of two-dimentional SSD is had also been proposed, while realizing laser beam
In the beam smoothing of two orthogonal directions in the direction x and the direction y；But since laser beam is inevitable in far field presence in two-dimentional SSD
Coherent phenomena, and then have also been proposed tripartite to the even sliding technology of SSD, the even sliding technology is by tending to the frequency of near field laser beam
Randomly, target surface irradiation uniformity is further improved.However, there are light channel structure complexity, adjusting are tired for the even sliding technology of three direction SSD
The disadvantages of difficult.
In order to make up the deficiency of striated pattern list dispersion direction, Circular gratings, spiral grating and array grating are proposed.Wish
By the dispersion mode of special Circular gratings, spiral grating and array grating, to obtain more preferably beam smoothing effect.Circular gratings exist
Radially focal spot has apparent even sliding effect, i.e., has preferable inhibitory effect to the diffraction fringe around circumference groove.It is insufficient
Place is that, due to not having spectrum angle dispersion in circumferencial direction, diffraction fringe largely exists.The dispersion direction of spiral grating is in circumference
Direction, since closer to circle center, grating line is closeer, thus increases difficulty of processing.However at separate circle center,
The dispersion measure due to caused by grating is smaller, to obtain suitable chromatic dispersion effects, need to increase total groove of grating, this will further increase
Big difficulty of processing.Array grating introduces multiple dispersion directions, however theoretical research shows that increasing for raster unit number can't
Further improve the even sliding effect of focal spot, while increasing for unit number will increase actual difficulty of processing.
Summary of the invention
The purpose of the present invention is to overcome defect and deficiency in the presence of the prior art, a kind of inertial confinement is provided
Based on the smoothing by spectral dispersion new method of compound grating in fusion facility, and realize the smoothing by spectral dispersion dress of this method
It sets.This method is that a smoothing by spectral dispersion dress based on compound grating is added in inertially confinement fusion device optical transport chain
It sets, that is, the even cunning of laser beam far-field focus in different directions is able to achieve, to improve laser in a shorter integration time
The uniformity of far field beam irradiation improves its uniformity to target surface irradiation.
Smoothing by spectral dispersion method and even cunning in inertially confinement fusion device proposed by the present invention based on compound grating
Device can be used for directly driving and drive in inertially confinement fusion device indirectly, to improve the uniformity irradiated to target surface.
To achieve the above object, the present invention is realized using the technical solution being made of following technical measures.
Design concept of the invention is: in the preamplifier system in Laser Driven inertially confinement fusion device optical transport chain
Or after main amplification system, a smoothing by spectral dispersion device based on compound grating is added, time phase first is carried out to laser beam
Position modulation carries out region spectral dispersion for laser beam characteristic, then to laser beam, to realize the multi-party of laser beam far field speckle
To sweeping, so that the far-field focus of laser beam be made to realize comprehensive even cunning, i.e. improvement laser beam in a shorter integration time
To the uniformity of target surface irradiation.
The smoothing by spectral dispersion device based on compound grating is made of phase-modulator and compound grating；Its
Middle phase-modulator is used to carry out needed for spectrum angle dispersion laser beam generation time phase-modulation to generate compound grating
The bandwidth wanted；Compound grating is used to control the dispersion direction of laser beam.In order to guarantee compound grating even sliding effect and
The difficulty of processing of compound grating is reduced, used compound grating is plane transmission grating.Simultaneously in order to guarantee dispersion after
The symmetry of laser beam is transmitted, and the central axis of the compound grating and the central axis of incoming laser beam are conllinear, and will be compound
The dispersion area of type grating is divided into two parts: using the central axial outer border circular areas of compound grating as dispersion area i, half
Diameter is a certain fixed value, and dispersion is dispersion mode I, which can be one-dimensional dispersion or diameter crossed disperstion, and border circular areas
Region in addition is dispersion area ii, and dispersion is dispersion mode II, which is circumferencial direction dispersion or radial color
It dissipates.In the optical transport chain, seed light output unit output laser beam successively pass through preamplifier system, phase-modulator,
Compound grating, main amplification system, frequency translation unit and continuous phase plate (CPP), last line focus lens focus to target surface；
By the laser beam of phase modulator modulation when by compound grating, the laser beam of border circular areas is according to dispersion mode I
Dispersion is carried out, the laser beam other than border circular areas is in and carries out dispersion according to dispersion mode II.Two-part dispersion area is selected
When taking reasonable dispersion area and dispersion mode, the speckle inside far-field focus can be made in multi-direction quick sweeping, thus short
Focal spot is smoothed out in the time of integration in the modulated structure of dispersion direction, to improve the uniformity that laser beam irradiates target surface.
Based on the smoothing by spectral dispersion method of compound grating, packet in a kind of inertially confinement fusion device provided by the invention
Include following steps:
(1) in Laser Driven inertially confinement fusion device optical transport chain, a smoothing by spectral dispersion device is added, and adjust
The modulating frequency ω of phase-modulator in this devicemParameter value；
(2) phase-modulator described in step (1) carries out Temporal modulation to incoming laser beam in optical transport chain；
(3) incoming laser beam after the phase modulated device modulation described in step (2) in optical transport chain, then pass through spectrum
Compound grating in the even sliding device of dispersion；
(4) incoming laser beam described in step (3) passes through compound grating, the chromatic dispersion region point of compound grating
For dispersion area i and dispersion area ii two parts, laser beam is respectively simultaneously by the dispersion area i of compound grating and dispersion area
The spectral dispersion of domain ii progress different directions；
(5) laser beam successively passes through inertial confinement fusion after spectral dispersion in the optical transport chain described in step (4)
Beam expander, main amplification system, continuous phase plate in device, last line focus lens focus to target surface；The far-field focus of laser beam
When carrying out the spectral dispersion of different directions by compound grating, cause far-field focus inside speckle in respective dispersion direction
It quickly sweeps, realizes within the short time of integration to the even cunning of target surface, the i.e. uniformity of improvement target surface irradiation.
In above-mentioned technical proposal, the smoothing by spectral dispersion device of addition described in step (1) is filled in inertial confinement fusion
It sets among the preamplifier system in optical transport chain, or smoothing by spectral dispersion device is added after main amplification system.
In above-mentioned technical proposal, the smoothing by spectral dispersion device of addition described in step (1) is by phase-modulator and compound
Type grating composition.
In above-mentioned technical proposal, the outer diameter of compound grating and incoming laser beam bore in the smoothing by spectral dispersion device
It is identical.
Laser beam described in step (2) of the present invention after phase modulator modulation is to obtain spectrum widening, laser beam
Electric field strength may be expressed as:
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 (3) of the present invention carries out the table after spectral dispersion by compound grating
Up to formula are as follows:
Wherein,
In formula, r is the radius of round dispersion area i,For the abbe number of compound grating border circular areas i,It is multiple
The dispersion direction of mould assembly grating circle dispersion area i；For the abbe number of compound grating dispersion region ii,It is compound
The dispersion direction of grating dispersion region ii, and
When compound grating border circular areas i uses one-dimensional linear dispersion,
When being dissipated when compound grating border circular areas i is using radial color,
When compound grating region ii uses circumferencial direction dispersion,
When compound grating region ii uses diameter crossed disperstion,
In the formula of (5)~(8), diameter crossed disperstion is realized usually using circle groove, realizes circle using star-like ruling grating
Circumferential direction dispersion.
In time of integration Δ t described above, far-field intensity distribution are as follows:
In formula, Δ t is the time of integration,It is distributed for laser beam Near-field optical field,For continuous phase plate (CPP)
Additive phase, " FT " indicates Fourier transformation, and " | | " indicates to take absolute value.
It is provided by the invention to realize the smoothing by spectral dispersion side based on compound grating in the inertially confinement fusion device
The even sliding device of method, including seed light output unit, preamplifier system, lens, beam expander, main amplification system, frequency conversion list
Member, continuous phase plate, condenser lens, target surface；It further include smoothing by spectral dispersion device according to the present invention, the spectral dispersion is even
Sliding device is made of phase-modulator and compound grating；It is described according to optical path: in the optical transport chain, from seed light output list
The laser beam of member output successively passes through preamplifier system, phase-modulator, compound grating, main amplification system, frequency conversion list
After member, continuous phase plate, last line focus lens focus to target surface；The far-field focus of laser beam is carried out by compound grating
When the dispersion of different directions, speckle inside far-field focus is caused to be realized in the quick sweeping of respective dispersion direction in shorter product
To the even cunning of target surface in timesharing, that is, improve the uniformity that laser beam irradiates target surface.
In above-mentioned technical proposal, the smoothing by spectral dispersion device is located among the preamplifier system in optical transport chain or master
After amplification system.
In above-mentioned technical proposal, the phase-modulator in the smoothing by spectral dispersion device is electrooptic modulator, to realize
To the sinusoidal phase modulation of laser beam in optical transport chain.
In above-mentioned technical proposal, the outer diameter of compound grating and incoming laser beam bore in the smoothing by spectral dispersion device
It is identical.
In above-mentioned technical proposal, the compound grating in the smoothing by spectral dispersion device uses plane transmission grating.
In above-mentioned technical proposal, in the smoothing by spectral dispersion device compound grating by high damage threshold plane transmission
Grating is process.
Smoothing by spectral dispersion method and even cunning in inertially confinement fusion device of the present invention based on compound grating
Device, under the premise of continuous phase plate is used in inertially confinement fusion device optical transport chain, the smoothing by spectral dispersion device
It can be placed in the big system of prevention, or after main amplification system, so as to cause speckle inside laser beam focal spot in optical transport chain
It is quickly swept in different dispersion areas along different directions, to realize the far field speckle to laser beam in optical transport chain compound simultaneously
The even cunning in type grating dispersion direction.
Possessed advantage and beneficial technical effect are as follows compared with prior art by the present invention:
1, present invention firstly provides the light based on compound grating in the Laser Driven system of inertially confinement fusion device
Spectrum color dissipates even sliding method, and provides a kind of smoothing by spectral dispersion device for realizing this method, realizes laser beam in optical transport chain
Beam smoothing of the far field speckle in compound grating dispersion direction.The smoothing by spectral dispersion device using compound grating into
The dispersion of row subregion is different from the dispersion of traditional array type grating, and traditional array type raster unit number is more, and dispersion area is drawn
Point mode is also different；If Circular gratings dispersion direction be it is radial, spiral grating dispersion direction is circumferencial direction, dispersion direction compared with
It is single.
2, the smoothing by spectral dispersion method in inertially confinement fusion device of the present invention based on compound grating and even
Sliding device, since dispersion mode increases, can effectively reduce laser beam in far field and generate the strong of striated compared with existing 1D-SSD
Spend the generation of modulation；Compared with 2D-SSD, the laser beam by compound grating dispersion be can effectively avoid in the relevant existing of far field
As.
3, the smoothing by spectral dispersion method in inertially confinement fusion device of the present invention based on compound grating and even
Sliding device is to carry out subregion dispersion to laser beam using compound grating, due to using circumferencial direction color in dispersion area ii
It dissipates, when grating compound in smoothing by spectral dispersion device is placed in preamplifier system, can effectively avoid due to grating dispersion
The focal spot size of introducing becomes larger and reduces the via hole efficiency of spatial filter；When grating compound in smoothing by spectral dispersion device is put
When being placed in after main amplification system, can effectively avoid causes since the focal spot size that grating dispersion introduces becomes larger in the black chamber of fusion
Plug-hole problem at injection hole.
4, the smoothing by spectral dispersion method in inertially confinement fusion device of the present invention based on compound grating and even
Sliding device, compound grating and existing special grating be for example in the smoothing by spectral dispersion device: Circular gratings, spiral grating, battle array
Column grating etc. is compared, smaller in the incisure density of dispersion area i, thus difficulty of processing is smaller, and structure is relatively easy and is easier to
It is processed in heavy caliber.
Detailed description of the invention
Fig. 1 is that the embodiment of the present invention 1 realizes spectral dispersion based on compound grating in the inertially confinement fusion device
The even sliding device of even sliding method is placed in the structural schematic diagram in preamplifier system；
Fig. 2 is that the embodiment of the present invention 2 realizes spectral dispersion based on compound grating in the inertially confinement fusion device
The even sliding device of even sliding method is placed in the structural schematic diagram after main amplification system；
Fig. 3 is the even of the smoothing by spectral dispersion method in inertially confinement fusion device of the present invention based on compound grating
The structural schematic diagram of compound grating in sliding device；
Fig. 4 is that have in smoothing by spectral dispersion method in inertially confinement fusion device of the present invention based on compound grating
Focal spot when continuous phase plate, wherein (a) is the focal spot of compound grating light beam；It (b) is the coke of existing 1D-SSD light beam
Spot；It (c) is the focal spot of existing spiral grating light beam；
Fig. 5 is the color of the smoothing by spectral dispersion method in inertially confinement fusion device of the present invention based on compound grating
Dissipate direction schematic diagram, wherein (a) is compound grating beam smoothing direction；It (b) is existing 1D-SSD beam smoothing direction；
It (c) is existing spiral grating beam smoothing direction；
Fig. 6 is that have in smoothing by spectral dispersion method in inertially confinement fusion device of the present invention based on compound grating
When continuous phase plate, compound grating, 1D-SSD, spiral grating three kinds of beam smoothing schemes under, the FOPAI of focal spot is bent
Line；
Fig. 7 is to be based on having company in the even sliding method of compound grating spectrum dispersion in inertially confinement fusion device of the present invention
When continuous phase-plate, compound grating, 1D-SSD, spiral grating three kinds of beam smoothing schemes under, luminous flux contrast
Contrast with time of integration Δ t change curve.
In Fig. 1,1 seed light output unit, 2 preamplifier systems, 3 lens, 4 phase-modulators, 5 compound gratings, 6 expand
Beam device, 7 main amplification systems, 8 frequency translation units, 9 continuous phase plates, 10 condenser lenses, 11 target surfaces, 12 smoothing by spectral dispersion dress
It sets.
Specific embodiment
Invention is further described in detail with reference to the accompanying drawing and with specific embodiment, it is necessary to indicated herein to be
The embodiment described is only intended to further describe of the invention, and is not meant to be to any of the scope of the present invention
It limits.
Based on the smoothing by spectral dispersion method of compound grating, Yi Jiti in inertially confinement fusion device of the present invention
It is as shown in Figure 1 that the smoothing by spectral dispersion device of realization this method of confession is placed in the structure in preamplifier system.It is defeated including seed light
Unit 1 out, preamplifier system 2, lens 3, beam expander 6, main amplification system 7, frequency translation unit 8, continuous phase plate 9 focus
Lens 10, target surface 11；It further include smoothing by spectral dispersion device 12, the smoothing by spectral dispersion device 12 is by 4 He of phase-modulator
Compound grating 5 forms.Describe by optical path: the laser beam that the seed light output unit 1 exports successively 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
Converting unit 8, continuous phase plate 9, condenser lens 10 finally reach target surface 11；Further as shown in Figure 1, the optical transport chain
Middle laser beam is after phase-modulator 4 carries out Temporal modulation, and by compound grating 5, laser beam is distinguished simultaneously at this time
The dispersion of different directions is carried out by the dispersion area i and dispersion area ii of compound grating 5；Laser beam passes through spectral dispersion
Afterwards, successively pass through 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 causes speckle inside far-field focus when carrying out the dispersion of different directions by compound grating 5
In the quick sweeping of respective dispersion direction, realize in a shorter integration time to the even cunning of target surface 11, the i.e. irradiation of improvement target surface
Uniformity.
The present invention central axis of the compound grating 5 and enters to guarantee the symmetry transmission of laser beam after dispersion
The central axis for penetrating laser beam is conllinear, and the dispersion area of compound grating 5 is divided into two parts by incoming laser beam: i.e. with compound light
The central axial outer round dispersion area of grid 5 is divided into dispersion area i, and dispersion is dispersion mode I, and dispersion mode I can be with
For one-dimensional dispersion or diameter crossed disperstion, the circle dispersion area radius is the region of a certain fixed value；And round dispersion area with
Outer dispersion area is divided into dispersion area ii, and dispersion is dispersion mode II, dispersion mode II can for circumferencial direction dispersion,
Or diameter crossed disperstion.
In Fig. 2 of the present invention, realize that the spectral dispersion based on compound grating in the inertially confinement fusion device is even
It is as shown in Figure 2 that the smoothing by spectral dispersion device of sliding method is placed in the structure after main amplification system.It is described by optical path: the seed
The laser beam that light output unit 1 exports successively passes through preamplifier system 2, lens 3, beam expander 6, main amplification system 7, frequency conversion
Unit 8, phase-modulator 4 and compound grating 5 in smoothing by spectral dispersion device 12, continuous phase plate 9, condenser lens 10, most
Target surface 11 is reached afterwards；Further as shown in Figure 2, laser beam is after Temporal modulation in the optical transport chain, by compound
Type grating 5, laser beam carries out different directions by the dispersion area i and dispersion area ii of compound grating 5 simultaneously respectively at this time
Dispersion；Laser beam is after spectral dispersion, and using continuous phase plate 9, last line focus lens 10 focus on target surface 11；
The far-field focus of laser beam causes speckle inside far-field focus to exist when carrying out the dispersion of different directions by compound grating 5
The quick sweeping of respective dispersion direction, it is same to realize in a shorter integration time to the even cunning of target surface 11, i.e. improvement target surface spoke
According to uniformity.
In Fig. 3 of the present invention, the dispersion area i at center is the central axial outer round color with compound grating 5
Dissipate region；The dispersion area ii of outside is the dispersion area other than round dispersion area.
In Fig. 4 of the present invention, there is continuous phase plate in the smoothing by spectral dispersion method based on compound grating
When focal spot, it is seen that the focal spot of (a) compound grating light beam, without apparent diffraction fringe；(b) existing 1D-
The focal spot of SSD light beam, in groove direction, there are diffraction fringes；(c) focal spot of existing spiral grating light beam, in radial presence
Diffraction fringe.
In Fig. 5 of the present invention, the dispersion of compound grating is divided into both direction, and dispersion area i is one-dimensional linear color
It dissipates, dispersion area ii is circumferencial direction dispersion；Existing 1D-SSD is one-dimensional linear dispersion；Existing spiral grating is radial direction
Dispersion.
Embodiment 1
The present embodiment is using the smoothing by spectral dispersion based on compound grating in inertially confinement fusion device as shown in Figure 1
The even sliding device of method is placed in the structural schematic diagram in preamplifier system 2.
Phase-modulator 4 in the present embodiment in smoothing by spectral dispersion device used is electrooptic modulator, described compound
The put position of grating is in preamplifier system；The dispersion direction of the dispersion area i of compound grating 5 used is the one-dimensional direction x color
It dissipates, abbe number isThe dispersion area ii of compound grating is circumferencial direction dispersion, and grating is always carved
The dispersion area of line M=20000, composite grating dispersion area i and dispersion area ii are identical, time of integration Δ t=10ps.
The incoming laser beam bore is 30mm, and the outer diameter of compound grating 5 used is identical as laser beam bore.
The smoothing by spectral dispersion method based on compound grating specific steps are as follows:
(1) in Laser Driven inertially confinement fusion device optical transport chain preamplifier system 2, a smoothing by spectral dispersion is added
Device, and adjust the parameter value of Temporal modulation device 4 in this device, wherein modulating frequency ωm=17GHZ and modulation depth δ
=2.38；
(2) sinusoidal time phase-modulation is carried out to laser beam in optical transport chain with step (1) phase-modulator 4；
(3) incoming laser beam is after the modulation of phase-modulator 4 in the optical transport chain described in step (2), then by multiple
Mould assembly grating 5, the compound grating outer diameter are identical as incoming laser beam bore 30mm；
(4) dispersion area of compound grating 5 is divided by the incoming laser beam described in step (3) by compound light 5
Dispersion area i and dispersion area ii two parts, respectively simultaneously by the dispersion area i and dispersion area ii of compound grating 5
Carry out the dispersion of different directions；Dispersion area i is one-dimensional x orientational dispersion, and abbe number isDispersion area
Domain ii is circumferencial direction dispersion, the total groove M=20000 of grating；
(5) in the optical transport chain described in step (4) incoming laser beam after spectral dispersion, successively by beam expander 6,
Main amplification system 7, frequency translation unit 8, continuous phase plate 9, last line focus lens 10 focus on target surface 11；Laser beam it is remote
Field focal spot causes far-field focus inside speckle in respective dispersion side when carrying out the dispersion of different directions by compound grating 5
To quick sweeping, realize in a shorter integration time to the even cunning of target surface 11, i.e. the uniformity that irradiates of improvement target surface 11.
For convenience of comparison, by the smoothing by spectral dispersion method of embodiment 1 and typical one-dimensional 1D-SSD and spiral grating into
Row compares, and wherein the parameter of 1D-SSD is according to document (S.Skupsky, R.W.Short, T.Kessler, et al..Improved
laser beam uniformity using the angular dispersion of frequency modulated
Light.J.Appl.Phys.66,3456 (1989)) it is chosen, i.e. the modulating frequency ω of Temporal Phase Modulationm=
2.5GHz, modulation depth are δ=12, and grating dispersion coefficient isWherein the parameter of spiral grating is according to text
Offer (Rui Zhang, Xiaomin Zhang, Zhan Sui, and Hai Ming.Research on target uniform
irradiation method using linearly modulated light and special grating
Dispersion.Optics&Laser Technology, 43:1073-1077) it is chosen.
Fig. 4~Fig. 7 be embodiment 1 in based on the smoothing by spectral dispersion method of compound grating to far-field focus uniformity
Improvement shown that acquired results have absolutely proved the light of the present invention based on compound grating from each figure
Spectrum color dissipates validity, the feasibility of even sliding method and even sliding device.
Shown in Fig. 4, when compared continuous phase plate 9, radial even sliding method, 1D-SSD, radial even cunning and 1D-SSD connection
It closes and is distributed using the focal spot under three kinds of schemes.In Fig. 4, (a) is composite grating focal spot, no apparent striated inside focal spot
Intensity modulation, and focal spot size and be not significantly changed；It (b) is existing 1D-SSD focal spot, focal spot obtains even cunning in the direction y, deposits
In the intensity modulation of apparent striated；It (c) is existing spiral grating focal spot, focal spot is in the light for radially having apparent striated
It emphasizes to make.
Fig. 5 show the dispersion that radial even sliding method, 1D-SSD, radial even cunning and 1D-SSD are used in combination under three kinds of schemes
Direction schematic diagram.In Fig. 5, (a) is the even sliding direction of composite grating, and dispersion is divided into both direction, and dispersion area i is one-dimensional linear
Dispersion, dispersion area ii are circumferencial direction dispersion；It (b) is existing 1D-SSD beam smoothing direction, 1D-SSD is the direction x color
It dissipates, (c) is existing spiral grating beam smoothing direction, even sliding direction is diameter crossed disperstion.In order to which quantitative analysis focal spot is uniform
The improvement degree of property, is evaluated, focal spot luminous flux contrast is smaller to show coke using focal spot luminous flux contrast (Contrast)
Spot uniformity is better；Its formula is expressed as follows:
In formula, Ii,j(xf,yf) it is (xf,yf) light intensity at position；ImeanFor average intensity.
For the improvement degree of hot spot inside the even sliding technology focal spot of quantitative analysis beam, using Fractional Power
Above Intensity (FOPAI) curve is evaluated, and FOPAI curve shows the improvement of hot spot inside focal spot to moving to left
Better；Its formula is expressed as follows:
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, for 90% energy circle rate
Region is calculated.
Its light FOPAI and flux pair are calculated separately to the light distribution of focal spot shown in Fig. 4 using formula (10) and (11)
Than line of writing music, obtain shown in Fig. 6 and Fig. 7.
Shown in Fig. 6, when having used continuous phase plate 9, the even sliding method of compound grating, 1D-SSD and spiral grating are made respectively
Roughly the same with the FOPAI curve of lower focal spot, hot spot is not significantly increased inside focal spot.
Shown in Fig. 7, when having used continuous phase plate 9, the even sliding method of compound grating, 1D-SSD and the effect of spiral grating
Under, the luminous flux contrast of focal spot is close, and the even sliding effect of beam is suitable.
The displaying of 1 and Fig. 4-Fig. 7 through the foregoing embodiment, shows the base in inertially confinement fusion device of the present invention
Having for target surface can be realized in shorter time of integration 10ps in the smoothing by spectral dispersion method of compound grating and even sliding device
Imitate even cunning.
Embodiment 2
The present embodiment is using the smoothing by spectral dispersion based on compound grating in inertially confinement fusion device as shown in Figure 2
The even sliding device of method is placed in the structural schematic diagram after main amplification system 7.
The dispersion direction of the dispersion area i of compound grating 5 used in this example is one-dimensional x orientational dispersion, abbe number
ForThe dispersion area ii of compound grating is diameter crossed disperstion, and abbe number is
Composite grating dispersion area i is identical as the dispersion area of dispersion area ii, time of integration Δ t=10ps.
The incoming laser beam bore is 360mm, and compound grating outer diameter used is identical as this incoming laser beam bore.
Other operating process and step are same as Example 1, and equally, incoming laser beam passes through phase in the optical transport chain
After modulator 4 is modulated, by compound grating 5, at this time laser beam respectively simultaneously by the dispersion area i of compound grating 5 with
The dispersion of dispersion area ii progress different directions；Laser beam is after spectral dispersion, by 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 not Tongfang by compound grating 5
To dispersion when, cause speckle inside far-field focus to be realized in the quick sweeping of respective dispersion direction in the shorter time of integration
The interior even cunning to target surface 11, the i.e. uniformity of improvement target surface irradiation.
When compound grating dispersion region i uses one-dimensional linear dispersion, and dispersion area ii uses diameter crossed disperstion, equally may be used
It is effectively improved the uniformity of target surface irradiation.
Embodiment of the present invention only gives specific example application, but the laser for being engaged in inertial confinement fusion drives
For researcher in dynamic system, can also be designed according to the above enlightenment it is a variety of in inertially confinement fusion device based on
The spectral dispersion beam smoothing structure of compound grating, this is still considered being covered by among the present invention.
Claims (2)
1. based on the smoothing by spectral dispersion method of compound grating in a kind of inertially confinement fusion device, it is characterised in that including with
Lower step:
(1) in the inertially confinement fusion device optical transport chain of Laser Driven, a smoothing by spectral dispersion device (12) is added, and adjust
Save the modulating frequency ω of Temporal modulation device (4) in this devicemParameter value；
(2) the Temporal modulation device (4) described in step (1) carries out time phase tune to incoming laser beam in optical transport chain
System；
(3) through the modulated incoming laser beam of the Temporal modulation device (4) in step (2), then it is even by spectral dispersion
Compound grating (5) in sliding device (12)；
(4) incoming laser beam described in step (3) by compound grating (5) by its dispersion area be divided into dispersion area i and
Dispersion area ii two parts, laser beam carry out the dispersion of different directions by dispersion area i and dispersion area ii simultaneously respectively；
(5) laser beam described in step (4) is after spectral dispersion, successively by 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 causes far-field focus when carrying out the spectral dispersion of different directions by compound grating (5)
Internal speckle is realized within the short time of integration in the quick sweeping of respective dispersion direction to the even cunning of target surface, i.e. improvement target surface spoke
According to uniformity.
2. according to claim 1 based on the smoothing by spectral dispersion method of compound grating, it is characterised in that institute in step (1)
The smoothing by spectral dispersion device (12) for stating addition is made of Temporal modulation device (4) and compound grating (5).
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