Nanosecond laser spatio-temporal regulation method based on double-cone collision direct-drive laser apparatus, and apparatus

Abstract

A nanosecond laser spatio-temporal regulation method based on a double-cone collision direct-drive laser apparatus, and an apparatus. The regulation method comprises: when a near-isentropic compression waveform for driving implosion is satisfied, redistributing temporal waveforms of all sub-beams in an apparatus, involving: using a fraction of laser beams to generate a low-energy foot pulse, which is focused on a relatively large target surface, such that the target surface slowly contracts inwards under the action of the low-energy foot pulse and contracts to a relatively small target surface by the end of the duration of the low-energy foot pulse; and at this time, using the remaining majority of laser beams to generate a main drive pulse, which is focused on the relatively small target surface, thereby realizing zooming.

Description

Nanosecond laser spatiotemporal control method and device for double-cone collision direct-drive laser device Technical Field

[0001] The present invention relates to the problems of cross-beam energy transfer and target surface irradiation uniformity in a laser directly driven inertial confinement fusion (ICF) device, and in particular to a nanosecond laser spatiotemporal control method and device based on a double-cone collision directly driven laser device. Background Art

[0002] Two common laser-driven methods for inertial confinement fusion (ICF) are direct and indirect. Indirect laser driving does not directly irradiate the target pellet, but instead generates X-rays by irradiating the hohlraum wall, which are then used to heat and compress the target pellet. The advantage of indirect laser driving is greater uniformity of the radiation source driving ablation. However, the X-ray generation process inevitably results in energy loss, requiring higher laser energy, and the laser-plasma interaction (LPI) process within the hohlraum is relatively complex. Direct laser driving requires multiple laser beams to uniformly irradiate the target pellet, which is loaded with cryogenic nuclear fuel. The energy required to couple the driving laser to the deuterium-tritium (DT) fuel is approximately five to six times greater than indirect laser driving, but direct laser driving requires higher laser beam uniformity. Research has shown that direct laser driving requires irradiation uniformity of less than 1% on the target pellet surface. Direct laser driving effectively converts laser energy into kinetic energy of the target shell, compressing the fusion fuel to a high density, achieving the conditions for thermonuclear combustion (ρR ≥ 0.3 g / cm). 2 , where ρ is the mass density of the fuel and R is the radius of the pellet).

[0003] In direct-drive ignition designs, the laser beam spot size approaches the target focal spot diameter, leading to energy loss due to cross-beam energy transfer (CBET) between multiple beams. CBET is a laser plasma instability caused by the overlapping wave fields of multiple beams, which causes the laser beams to exchange energy through diffraction on the ion acoustic wave grating in the overlapping region. This directly affects the uniform compression of the target in the ICF, affecting the beam-target coupling efficiency and thus reducing the fusion yield. Studies have shown that reducing the laser beam spot diameter can compensate for the kinetic energy lost due to CBET, but at the same time, low-order mode perturbations increase, irradiation uniformity decreases, and affects implosion performance. Dual-state zoom can simultaneously mitigate CBET and low-order mode perturbations, making the implosion process more stable.

[0004] Traditional OMEGA direct drive requires 60 beams to be uniformly irradiated across an entire spherical surface with a diameter of ~850 μm. Its power balance requires a root mean square power imbalance of less than 1% within any 100 ps pulse interval. Therefore, OMEGA places extremely high demands on pulse temporal synchronization, the control accuracy of the time-power curve of each beam, and the consistency of the time-power curves across multiple laser beams. Therefore, to reduce the impact of CBET, the OMEGA device can only adopt a two-step zoom scheme based on spatial division multiplexing. This scheme utilizes a time-varying wavefront and a zoom phase plate (ZPP) to superimpose different phase structures on the beams at different times, ultimately achieving a time-varying far-field focal spot size. This zoom technology based on space division multiplexing can effectively overcome energy loss and CBET effect, but there are several major problems: (1) OMEGA uses an annular beam to generate the driving main pulse, which requires high control of the incident light field distribution; (2) The energy utilization rate of the incident light beam is low, and can only reach 75% at most; (3) Since the foot pulse is a non-saturated linear amplification in the entire amplification chain, its stability is more difficult to control than the stability of the main pulse. The power fluctuation of the foot pulse is too large, which will reduce the irradiation uniformity of the entire target sphere during the isentropic compression process and affect the mismatch of the timing and intensity of the shock wave, thereby reducing the surface density. (DHFroula, TJKessler, IVIgumenshchev, R.Betti, VNGoncharov, H.Huang, SXHu, E.Hill, JHKelly, DDMeyerhofer, A.Shvydky, and JDZuegel, "Mitigation of cross-beam energy transfer: Implication of two-state focal zooming on OMEGA," Physics of Plasmas 20 (2013).)

[0005] The Double-Cone Collider Ignition (DCI) scheme utilizes a near-isentropic nanosecond compression waveform for isentropic compression of fusion fuel within two opposing gold cones. Under the pinching action of the cones, the fusion fuel reaches extremely high speeds and densities, being confined and ejected from the cone openings. It then collides with the plasma ejected from the opposing cone, increasing the temperature and density of the fusion fuel. Because all beams in the Double-Cone Collider are constrained by the cones to strike only the same surface, the power balance requirements between beams can be reduced, requiring only the intensity balance of the superimposed beams on the two surfaces.

[0006] Summary of the Invention

[0007] In order to overcome the shortcomings of the above-mentioned prior art, the present invention proposes a nanosecond laser spatiotemporal control method and device based on double-cone collision direct drive, by directly driving the laser device with double-cone collision, for n / 2 laser pulses on a single cone, m of which are used to generate low-energy pulses focused on an initial radius of R. t The target surface is focused on the target to provide better illumination uniformity, and the remaining (n / 2-m) beam is used to generate a high-energy driving main pulse focused on a relatively small R b (R b =0.7R t ) on the target surface to reduce cross-beam energy transfer and improve beam-target coupling efficiency.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A nanosecond laser spatiotemporal control method based on a double-cone collision direct-drive laser device is characterized by redistributing the temporal waveforms of all nanosecond laser pulses in the double-cone collision direct-drive laser device while satisfying a near-isentropic compression waveform for driving implosion, comprising:

[0010] A small portion of the beam is used to generate a low-energy pulse, which is focused on a larger target surface. The target surface is then slowly contracted inwards by the low-energy pulse, shrinking to a smaller target surface at the end of the low-energy pulse duration.

[0011] The remaining majority of the light beam is used to generate the main driving pulse, which is focused on this smaller target surface to achieve zooming.

[0012] The duration of the near-isentropic compression waveform driving the implosion is 0 to τ, and the duration of the low-energy pulse is 0 to t d , the duration of the driving main pulse is t d ~τ,t d The corresponding target is from the initial radius R t Converge to 0.7R t For n / 2 nanosecond laser pulses on a single cone, m beams of light are used to generate low-energy pulses, which are focused on the initial radius R. t On the target surface, the energy of the low-energy pulse is converted into the kinetic energy of the target shell. The initial radius R t The target surface slowly shrinks inwards. When t d Converges to a smaller target surface R b (R b =0.7R t ), the high-energy driving main pulse generated by the remaining (n / 2-m) beams begins to work and focuses on a radius of R b on the target surface to achieve zoom.

[0013] Among them, the low energy pulse refers to the target pellet moving from the initial radius R t Reduced to 0.7R t The corresponding time-power curve, the high-energy driving main pulse refers to the target pellet from 0.7R t Continue to reduce the corresponding time-power curve. (Studies have shown that the optimal zoom position satisfies R b / R t = 0.7, which can further increase the implosion speed.)

[0014] The requirements for generating m-beam nanosecond laser pulses with low energy and sufficient pulses are as follows:

[0015] (1) Ensure that each nanosecond laser pulse is at a safe energy density of 4J / cm 2 To ensure the reliable operation of the device;

[0016] (2) Ensure that the load of the m nanosecond laser pulses that generate the low-energy sufficient pulses and the (n / 2-m) nanosecond laser pulses that generate the high-energy driving main pulses are equivalent;

[0017] (3) The m beams of nanosecond laser pulses that generate low-energy pulses are arranged as much as possible on a ring with the smallest angle with the polar axis, so as to maximize the irradiation uniformity of the driving laser on the target surface in the early stage.

[0018] The device for implementing the above-mentioned nanosecond laser space-time control method based on double-cone collision direct-driven laser device is characterized in that it includes a spectral dispersion grating, a transmission amplification component, a frequency doubling crystal, a continuous phase plate, a polarization control plate, a focusing lens and a target surface arranged in sequence along the transmission direction of the front-end seed source; the seed light output by the front-end seed source passes through the spectral dispersion grating and enters the transmission amplification component to amplify the beam aperture and energy, and then the fundamental frequency light is converted into tripled frequency light through the frequency doubling crystal, and then the far-field focal spot is shaped into a focal spot with a certain shape and size through the continuous phase plate, and then focused on the far-field target surface by the focusing lens after passing through the polarization control plate to form a shaped focal spot.

[0019] After each nanosecond laser pulse passes through the spectral dispersion grating, continuous phase plate, polarization control plate and focusing lens, the far-field light field distribution of each nanosecond laser pulse on the target surface can be expressed as:

[0020] In the formula is the near-field distribution of each nanosecond laser pulse, λ 3ωj 、k 3ωj and ω 3ωj are the central wavelength, wave vector and frequency corresponding to each nanosecond laser pulse, and are the phase modulations of the beam by the continuous phase plate and the spectral dispersion grating, respectively; f is the focal length of the focusing lens, and “FT” stands for Fourier transform. is the random phase distortion introduced during beam transmission, which can be expressed as:

[0021] Within the integration time Δt, the far-field light intensity distribution is:

[0022] Where Δt is the integration time.

[0023] Each of the nanosecond laser pulses is generated by a different front-end seed source, so that the time domain and frequency domain characteristics of each beam of light can be independently controlled.

[0024] Furthermore, the seed light source laser can tune the central wavelength.

[0025] Furthermore, the temporal pulse shaping unit can achieve precise control of the time-power curve, thereby realizing high-precision control of the generation time of each nanosecond laser pulse and high-precision time delay adjustment capability, with the control accuracy at the picosecond level.

[0026] Furthermore, the phase modulation unit can realize the control of the spectrum.

[0027] Furthermore, the spectral dispersion grating is used in combination with the phase modulation unit in the front-end seed source to obtain a time-varying speckle structure, thereby smoothing the focal spot within a specific time.

[0028] Furthermore, the target focal spot size of the continuous phase plate used in the transmission process of each nanosecond laser pulse is different. For low-energy pulses, the target focal spot size is slightly smaller than the initial radius R t target surface to provide better illumination uniformity; for high-energy driving main pulse, the target focal spot size is slightly smaller than the radius R b target surface to reduce the energy transfer of the cross beam and improve the beam-target coupling efficiency.

[0029] Furthermore, the polarization state of the polarization control plate can be linear polarization along the tangent or normal direction of the position of the light beam on the ring, left-handed or right-handed circular polarization, or elliptically polarized light for different nanosecond laser pulses, in order to reduce the correlation between the sub-beams.

[0030] Furthermore, the target surface positions of the m-beam low-energy foot pulse and the (nm)-beam high-energy driving main pulse are different, and the target surface position of the (nm)-beam high-energy driving main pulse is slightly behind.

[0031] The advantages of the present invention are as follows:

[0032] 1. The present invention proposes for the first time a nanosecond laser spatiotemporal control method based on a double-cone collision direct-drive laser device. By utilizing a minority of the light beams to generate low-energy pulses focused on a target surface with an initial radius, better illumination uniformity is provided. The remaining majority of the light beams are used to generate high-energy driving main pulses focused on a relatively small target surface, thereby reducing cross-beam energy transfer and improving beam-target coupling efficiency.

[0033] 2. The zoom control described in the present invention is achieved by using a small number of light beams to generate low-energy sufficient pulses, reducing the impact of front-end system electrical noise on waveform stability under low power, while increasing the gain saturation of the main amplification link, thereby improving the stability and control accuracy of the sufficient pulses as a whole, effectively improving the control accuracy of the time-power curve irradiated on the target surface, and better controlling the timing of the shock wave and the degree of consistency of the time intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1(a) is the benchmark time-power curve of the double-cone collision direct-drive laser device described in the present invention, and Figure 1(b) is the time-power curve of a single foot pulse and a single driving main pulse after using the zoom scheme of "4 foot pulses + 12 main pulses".

[0035] FIG2 shows the beam arrangement of the double-cone collision direct-drive laser device on a single cone in the present invention.

[0036] FIG3 is a diagram showing the optical path of each nanosecond laser pulse during transmission in the double-cone collision direct-drive laser device of the present invention.

[0037] FIG4 shows the variation of the irradiation uniformity of 4 foot pulses and 12 main pulses on the target surface with the integration time of the double-cone collision direct drive laser device in the present invention.

[0038] Figure 5 shows the irradiation results of the double-cone collision direct-drive laser device on the target surface at an integration time of 100 ps in the present invention, where (a) is the irradiation result of 4 beam foot pulses on the target surface of the initial radius of the target capsule, and (b) is the irradiation result of 12 beam driving main pulses on the target surface of 0.7 times the initial radius of the target capsule.

[0039] FIG6 is a time-power curve of a single foot pulse and a single driving main pulse of the double-cone collision direct drive laser device of the present invention after using the zoom scheme of “2 foot pulses + 14 main pulses”.

[0040] Figure 7 shows the irradiation results of the double-cone collision direct-drive laser device on the target surface at an integration time of 100 ps in the present invention, where (a) is the irradiation result of 2 beams of foot pulses on the target surface of the initial radius of the target capsule, and (b) is the irradiation result of 14 beams of driving main pulses on the target surface of 0.7 times the initial radius of the target capsule.

[0041] In the figure: 1-front-end seed source; 2-spectral dispersion grating; 3-transmission amplification component; 4-frequency doubling crystal; 5-continuous phase plate; 6-polarization control plate; 7-focusing lens; 8-target surface; 11-seed light source laser; 12-temporal pulse shaping unit; 13-phase modulation unit. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below with reference to specific embodiments in conjunction with the accompanying drawings. It is necessary to point out that the embodiments are only used to further describe the present invention and are not intended to limit the scope of protection of the present invention.

[0043] Example 1:

[0044] This embodiment primarily considers the physical requirements for compressing the target pellet in the dual-cone collision direct-drive laser device described in the present invention, and provides the physical basis for the design of a zoom scheme based on the "4 foot pulses + 12 main pulses" dual-cone collision direct-drive laser device, with a beam aperture of 375mm×375mm. The dual-cone collision direct-drive laser device requires the reference time-power curve irradiated on a single cone to be as shown in Figure 1(a). This is evenly distributed across 16 nanosecond laser pulses, with a single-path reference time-power curve contrast of 55:1 and a single-path peak power density of 711MW / cm 2 , the energy density is 2.97J / cm 2 .

[0045] In order to improve the control accuracy of the foot pulse and maximize the output capacity of the device, it is considered to use 4 of the beams to generate only foot pulses with a duration of 0 to 10 ns and a total energy of 6.20 kJ, and the remaining 12 beams to generate only driving main pulses with a duration of 10 to 15 ns and a total energy of 60.54 kJ, so that the sum of these 16 nanosecond laser pulses meets the benchmark time-power curve irradiated on the single cone.

[0046] Thus, the contrast ratio of a single foot pulse is 13:1, and the corresponding maximum peak power density distributed on a single foot pulse is 666 MW / cm 2 The energy density of a single foot pulse is 1.16 J / cm 2 The contrast ratio of the single-channel driving main pulse is 3.7:1, and the highest peak power density allocated to the single-channel driving main pulse is 948MW / cm 2 The energy density of the single-channel driving main pulse is 3.57J / cm 2 The time-power curves of a single foot pulse and a single driving main pulse are shown in Figure 1(b). Compared with the single-channel reference time-power curve, the waveform contrast is significantly reduced, which effectively improves the stability of the pulse.

[0047] Since the 12 main driving pulses begin to occur 10 ns after the other 4 foot pulses, these 12 main driving pulses use CPPs with small focal spots, while the other 4 foot pulses use CPPs with large focal spots, thereby realizing a zoom technology solution.

[0048] Please refer to FIG2 , which shows the beam arrangement of a double-cone collision-based direct-drive laser device on a single cone.

[0049] Please refer to Figure 3. First, consider the irradiation uniformity of the four foot pulses on the far-field large focal spot. The angle between these four foot pulses and the polar axis is 26°. During the generation, transmission and focusing process, each foot pulse passes through the front-end seed source 1, spectral dispersion grating 2, transmission amplification component 3, frequency doubling crystal 4, continuous phase plate 5, polarization control plate 6, focusing lens 7 and target surface 8 in sequence.

[0050] The relevant parameters of the spectral dispersion grating 2 are: time phase modulation frequency f m =17GHz, modulation depth m=2.4, grating dispersion coefficient δθ / δλ=215.68urad / nm.

[0051] The target focal spot of the continuous phase plate 5 is an elliptical focal spot, which becomes a circular focal spot with a radius slightly smaller than 1000 μm when projected onto the target surface.

[0052] The focal length of the focusing lens 7 is 5m; the initial radius R of the target surface 8 is t =1000um, the fundamental frequency center wavelength of each beam foot pulse is 1053nm, the tripled frequency center wavelength is 351nm, and the landing point accuracy is 30um rms.

[0053] In order to quantitatively analyze the change of focal spot uniformity with integration time, the luminous flux contrast (C) of the focal spot is used for evaluation. The smaller the luminous flux contrast of the focal spot, the better the focal spot uniformity. The calculation method of C is as follows:

[0054] Where, I i,j (x f ,y f ) is the focal plane (x f ,y f ) position, I mean (x f ,y f ) is the average light intensity on the focal plane.

[0055] When quantitatively analyzing the uniformity of the focal spot, the luminous flux contrast of the focal spot is calculated for the area with an 80% surrounding energy ratio. The results are shown in Figure 4. Figure 4(a) shows the variation of the irradiation uniformity of the four-beam foot pulse on the target surface 8 with the integration time. At an integration time of 100 ps, ​​the irradiation uniformity is 0.1740. The irradiation situation on the target surface is shown in Figure 5(a).

[0056] Similarly, the irradiation of the small focal spot by 12 driving main pulses is considered. The 12 driving main pulses include 4 beams with an angle of 32° to the polar axis and 8 beams with an angle of 45° to the polar axis.

[0057] For these 12 main driving pulses, the radius of the target surface 8 is 0.7R t The change of the luminous flux contrast of the focal spot in the area of ​​80% surrounding energy ratio with the integration time is shown in Figure 4(b). At an integration time of 100 ps, ​​the irradiation uniformity is 0.2072, and the irradiation situation on the target surface is shown in Figure 5(b).

[0058] Example 2:

[0059] This example primarily considers the physical basis for designing a zoom scheme based on a dual-cone collision direct-drive laser device with two foot pulses and 14 main pulses. The beam aperture is 375 mm × 375 mm. The time-power curves for a single foot pulse and a single main pulse, obtained using this partitioning scheme, are shown in Figure 6.

[0060] Thus, the highest peak power density corresponding to the single-channel foot pulse is 1332 MW / cm 2 The energy density of a single foot pulse is 2.32 J / cm 2 The highest peak power density distributed on a single-channel driving main pulse is 812MW / cm 2 The energy density of the single-channel driving main pulse is 3.06J / cm 2 .

[0061] In addition, under this zoom scheme, two adjacent foot pulses of the four foot pulses described in Example 1 are selected as the two foot pulses of Example 2, acting on R t The uniformity of the focal spot was quantitatively analyzed. The flux contrast within the focal spot region with an 80% surrounding energy ratio was calculated at an integration time of 100 ps, ​​resulting in a value of 0.1157. Figure 7(a) shows the irradiation on the target surface.

[0062] Also consider the irradiation of the remaining 14 driving main pulses on the small focal spot. The radius of the target surface 8 is 0.7R t, at an integration time of 100 ps, ​​the luminous flux contrast of the focal spot in the area of ​​80% surrounding energy ratio is 0.2117, and the irradiation situation on the target surface is shown in Figure 7(b).

[0063] Compared with Example 1, although the irradiation uniformity of the large focal spot using two foot pulses in Example 2 is better (this is because the polarization directions of the two beams of light can be controlled to be perpendicular to each other, which is equivalent to incoherent superposition on the target surface), the highest peak power density of the single foot pulse in Example 2 is too high, which can easily cause damage to optical components.

[0064] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may also undergo various modifications and variations.

Claims

1. A nanosecond laser spatiotemporal control method based on a double-cone collision direct drive laser device, characterized in that: The method redistributes the time waveforms of all nanosecond laser pulses in the double-cone collision direct drive laser device under the condition of satisfying the near-isentropic compression waveform driving the implosion, including: A small portion of the beam is used to generate a low-energy pulse, which is focused on a larger target surface. The target surface is then slowly contracted inwards by the low-energy pulse, shrinking to a smaller target surface at the end of the low-energy pulse duration. The remaining majority of the light beam is used to generate the main driving pulse, which is focused on this smaller target surface to achieve zooming.

2. The nanosecond laser spatiotemporal control method based on a double-cone collision direct drive laser device according to claim 1, characterized in that: The duration of the near-isentropic compression waveform driving the implosion is 0 to τ, and the duration of the low-energy pulse is 0 to t d , the duration of the driving main pulse is t d ~τ,t d The corresponding target is from the initial radius R t Converge to 0.7R t The corresponding moment.

3. The nanosecond laser spatiotemporal control method based on a double-cone collision direct drive laser device according to claim 1, characterized in that: The number of all nanosecond laser pulses in the double-cone collision direct-drive laser device is n. Under the condition of ensuring the intensity balance of the total power of the n / 2 nanosecond laser pulses on the upper and lower cone surfaces, the time waveform of each laser beam is redesigned so that the sum of the n / 2 nanosecond laser pulses satisfies the near-isentropic compression waveform for driving the implosion.

4. The nanosecond laser spatiotemporal control method based on a double-cone collision direct drive laser device according to claim 3, characterized in that: For n / 2 nanosecond laser pulses on a single cone, m beams, i.e. a small part of the beam, are used to generate low-energy pulses and are focused on a larger target surface, i.e., with an initial radius of R. t On the target surface, the energy of the low-energy pulse is converted into the kinetic energy of the target shell. The initial radius R t The target surface slowly shrinks inwards. When t d At the moment the target surface converges to a target radius of R b When a smaller target surface is used, R b / R t = 0.7, the remaining (n / 2-m) beam, that is, the high-energy driving main pulse generated by the remaining majority of the beam, is focused on a radius of R b on the target surface to achieve zoom.

5. The nanosecond laser spatiotemporal control method based on a double-cone collision direct drive laser device according to claim 4, characterized in that: The m-beam nanosecond laser pulses that generate low-energy sufficient pulses should meet the following conditions: -Each nanosecond laser pulse has a safe energy density of 4J / cm 2 Inside; - The load of m nanosecond laser pulses generating low-energy foot pulses and (n / 2-m) nanosecond laser pulses generating high-energy driving main pulses is equivalent; The nanosecond laser pulses with low energy and sufficient pulses generated by the -m beam are arranged as much as possible on the ring with the smallest angle with the polar axis to maximize the irradiation uniformity of the driving laser on the target surface in the early stage.

6. A device for implementing the nanosecond laser spatiotemporal control method based on a double-cone collision direct drive laser device according to any one of claims 1 to 5, characterized in that: The invention comprises a spectral dispersion grating (2), a transmission amplification component (3), a frequency doubling crystal (4), a continuous phase plate (5), a polarization control plate (6), a focusing lens (7) and a target surface (8) which are sequentially arranged along the transmission direction of a front-end seed source (1); the seed light outputted by the front-end seed source (1) passes through the spectral dispersion grating (2) and enters the transmission amplification component (3) to amplify the beam aperture and energy, and then passes through the frequency doubling crystal (4) to convert the fundamental frequency light into tripled frequency light, and then passes through the continuous phase plate (5) to shape the far-field focal spot into a focal spot with a certain shape and size, and then passes through the polarization control plate (6) and is focused by the focusing lens (7) on the far-field target surface (8) to form a shaped focal spot.

7. The device according to claim 6, characterized in that N nanosecond laser pulses are generated by different front-end seed sources (1), so that the time domain and frequency domain characteristics of each beam can be independently controlled.

8. The device according to claim 6, characterized in that The front-end seed source (1) comprises a seed light source laser (11), a time pulse shaping unit (12), and a phase modulation unit (13) which are sequentially placed on the same optical axis; The seed light source laser (11) is used to tune the central wavelength; The time pulse shaping unit (12) is used to accurately control the time-power curve, thereby achieving high-precision control of the generation time of each nanosecond laser pulse and high-precision time delay adjustment capability, with the control accuracy being at the picosecond level; The phase modulation unit (13) is used to achieve spectrum control.

9. The device according to claim 8, characterized in that The spectral dispersion grating (2) is used in combination with the phase modulation unit (13) in the front-end seed source (1) to obtain a speckle structure that changes with time, thereby smoothing the focal spot within a specific time.

10. The device according to claim 8, characterized in that The target focal spot size of the continuous phase plate (5) used in the transmission process of each nanosecond laser pulse is different. For low-energy pulses, the target focal spot size is slightly smaller than the initial radius R. t The target surface is designed to provide better illumination uniformity; for the high-energy driving main pulse, the target focal spot size is slightly smaller than the radius R b target surface to reduce the energy transfer of the cross beam and improve the beam-target coupling efficiency.

11. The device according to claim 8, characterized in that The polarization state of the polarization control plate (6) can be linear polarization along the tangent or normal direction of the position on the ring where the light beam is located, or it can be left-handed or right-handed circular polarization, or elliptically polarized light for different nanosecond laser pulses, thereby reducing the correlation between the sub-beams.

12. The device according to claim 8, characterized in that The target surface (8) positions of the m beam low-energy sufficient pulses and the (nm) beam high-energy driving main pulse are different, and the target surface (8) position of the (nm) beam high-energy driving main pulse is slightly backward.

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