Method and device for spatiotemporal control of nanosecond laser of double-cone counter-collision direct-drive laser device

Abstract

The present application relates to a kind of nanosecond laser space-time control methods based on double-cone pair collision direct drive laser device, in the case of meeting the nearly isentropic compression waveform of driving implosion, the time waveform of all sub-beams in device is redistributed, a small part of beam is used to generate low-energy foot pulse, and is focused on larger target surface, target surface is slowly contracted under the action of low-energy foot pulse, and is contracted to a smaller target surface at the end of the duration of low-energy foot pulse, then the majority of remaining beam is used to generate driving main pulse, and is focused on this smaller target surface, so as to realize zooming.The method reduces the waveform contrast of sub-beam by redistributing the time-power curve of all sub-beams, can realize higher precision control of time-power curve on target surface, also effectively reduces the loss caused by energy transfer (CBET) of cross-beam by zooming, improves beam-target coupling efficiency, and improves the irradiation uniformity of target pellet.

Description

Technical Field

[0001] This invention relates to the problem of crossbeam energy transfer and target surface irradiation uniformity in a laser-driven inertial confinement fusion (ICF) device, specifically to a nanosecond laser timing control method and device based on a dual-cone collision direct-driven laser device. Background Technology

[0002] Laser-driven inertial confinement fusion (ICF) commonly employs two driving methods: direct driving and indirect driving. Indirect driving involves the laser not directly irradiating the target pellet, but rather generating X-rays by irradiating the black cavity walls, which are then used to heat and compress the target pellet. The advantage of indirect driving is better uniformity of the radiation source driving ablation; however, energy loss is inevitable during X-ray generation, requiring higher laser energy, and the laser-plasma interaction (LPI) process within the black cavity is relatively complex. Direct driving requires multiple laser beams to uniformly irradiate a target pellet containing cryogenic nuclear fuel. The energy of coupling the driving laser to the deuterium-tritium (DT) fuel is approximately 5-6 times that of indirect driving, but direct driving demands even higher uniformity of the laser beam. Studies have shown that direct driving requires a target pellet surface irradiation uniformity of less than 1%. Direct laser driving can effectively convert laser energy into target shell kinetic energy, compressing and accumulating the fusion fuel to a high density, achieving the conditions for thermonuclear combustion (ρR ≥ 0.3 g / cm³). 2 , where ρ is the mass density of the fuel and R is the radius of the target pellet.

[0003] In direct-drive ignition designs, the laser beam spot size is close to the target focal spot diameter. Cross-beam energy transfer (CBET) between multiple beams leads to energy loss. CBET is a laser-plasma instability, essentially caused by the overlapping wavefields of multiple beams, resulting in energy exchange between the laser beams through diffraction on the ion acoustic grating in the overlapping region. This directly affects the uniform compression of the target in the ICF, impacting beam-target coupling efficiency and thus reducing fusion yield. Studies show that reducing the laser beam aperture can compensate for the kinetic energy loss due to CBET, but simultaneously increases low-order mode perturbations, reduces irradiation uniformity, 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 of light to uniformly irradiate the entire spherical surface with a diameter of ~850µm. Its power balance requires less than 1% root-mean-square power imbalance within any 100ps pulse interval. Therefore, OMEGA places extremely high demands on pulse timing synchronization, the control precision of the time-power curve of each beam, and the consistency of the time-power curves among multiple laser beams. Thus, to reduce the impact of CBET (Concurrent-to-Earth Emissions), OMEGA devices can only employ a two-step zoom scheme based on spatial division multiplexing. This involves using a time-varying wavefront and a zoom phase plate (ZPP) to superimpose different phase structures on the beam at different times, ultimately obtaining 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 a ring beam to generate the driving master pulse, which requires high control of the incident light field distribution; (2) The energy utilization rate of the incident beam is low, and can only reach 75% at most; (3) Since the foot pulse is a non-saturated linear amplification in the whole amplification chain, its stability is more difficult to control than the stability in the main pulse. The power fluctuation of the foot pulse is too large, which will reduce the irradiation uniformity in the isentropic compression process of the entire target sphere and affect the timing and intensity mismatch 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 energytransfer: Implication of two-state focal zooming on OMEGA," Physics of Plasmas 20 (2013).)

[0005] The dual-cone collision ignition (DCI) scheme employs a near-isentropic nanosecond compression laser waveform, isentropically compressing the fusion fuel within two opposing gold cones. Under the constricting effect of the gold cones, the fusion fuel reaches extremely high velocity and density, and is constrained as it exits from the cone openings, colliding with plasma ejected from the opposing cones to achieve an increase in the temperature and density of the fusion fuel. Because all beams in the dual-cone collision device are constrained by the gold cones and can only strike the same cone surface, the power balance requirements between beams can be reduced; only the intensity balance of all beams superimposed on the two cone surfaces needs to be considered. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention proposes a time-space control method and apparatus for nanosecond lasers based on direct driving of biconical collisions. This method involves using m of the n nanosecond laser pulses from the biconical collision direct driving laser apparatus to generate low-energy pulses that are focused onto a point with an initial radius of R. t On the target surface, to provide better illumination uniformity, the remaining (n / 2-m) beam generates a high-energy driving master pulse that is focused onto a relatively small R. b (R b =0.7R t On the target surface, to reduce energy transfer of cross beams and improve beam-target coupling efficiency.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A nanosecond laser timing and control method based on a biconical collision direct-drive laser device is characterized by redistributing the time waveforms of all nanosecond laser pulses in the biconical collision direct-drive laser device while satisfying the near-isentropic compression waveform for driving implosion, including:

[0009] A small portion of the beam is used to generate a low-energy foot pulse, which is focused on a large target surface. Under the action of the low-energy foot pulse, the target surface slowly contracts inward, and at the end of the duration of the low-energy foot pulse, it contracts into a smaller target surface.

[0010] The remaining majority of the beam is used to generate a driving main pulse, which is then focused onto this smaller target surface, thereby achieving zoom.

[0011] The duration of the near-isentropic compression waveform driving the implosion is 0–τ, and the duration of the low-energy foot pulse is 0–t. d The duration of the driving main pulse is t. d ~τ,t d This corresponds to the target pellet starting from its initial radius R. t Converging to 0.7R t The corresponding moment. For an n / 2 nanosecond laser pulse on a single cone, a low-energy pulse is generated by utilizing m beams of light within it, and then focused onto an 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, with an initial radius R. t The target surface slowly contracts inward, when at t d Converging to a smaller target area R at any time b (R b =0.7R t At this point, the high-energy driving main pulse generated by the remaining (n / 2-m) beam begins to act, focusing on a point with radius R. b Zooming is achieved on the target surface.

[0012] Among them, the low-energy pulse refers to the pulse emitted from the target pellet at its initial radius R. t Reduced to 0.7R t The corresponding time-power curve shows that the high-energy driving main pulse refers to the pulse from 0.7R. t Continue to decrease the corresponding time-power curve. (Studies show that the optimal zoom position satisfies R...) b / R t =0.7, which can further increase the implosion velocity.

[0013] The requirements for generating m-beam nanosecond laser pulses with low energy are as follows:

[0014] (1) Ensure that each nanosecond laser pulse is at a safe energy density of 4 J / cm². 2 This ensures the reliable operation of the device;

[0015] (2) Ensure that the loads of m nanosecond laser pulses that generate low-energy full pulses and (n / 2-m) nanosecond laser pulses that generate high-energy driving main pulses are equivalent;

[0016] (3) Arrange the m-beams of low-energy nanosecond laser pulses as close as possible to the ring with the smallest angle with the polar axis, so as to maximize the uniformity of early irradiation of the driving laser on the target surface.

[0017] The apparatus for implementing the above-mentioned nanosecond laser timing and control method based on a biconical collision direct-drive laser device is characterized by comprising 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 sequentially along the transmission direction of the front-end seed source; the seed light output from the front-end seed source enters the transmission amplification component after passing through the spectral dispersion grating for beam aperture and energy amplification, then the fundamental frequency light is converted into third harmonic light by the frequency doubling crystal, and the far-field focal spot is shaped into a focal spot with a certain shape and size by 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 the shaped focal spot.

[0018] After passing through a spectral dispersion grating, a continuous phase plate, a polarization control plate, and a focusing lens, the far-field optical distribution of each nanosecond laser pulse on the target surface can be expressed as:

[0019]

[0020] In the formula For the near-field distribution of each nanosecond laser pulse, λ 3ωj k 3ωj and ω 3ωj These represent the center wavelength, wave vector, and frequency corresponding to each nanosecond laser pulse. and These represent the phase modulation of the beam by the continuous phase plate and the spectral dispersive grating, respectively, where f is the focal length of the focusing lens, and "FT" represents the Fourier transform. The random phase distortion introduced during beam propagation can be expressed as:

[0021]

[0022] During the integration time Δt, the far-field light intensity distribution is as follows:

[0023]

[0024] In the formula, Δt is the integration time.

[0025] Each nanosecond laser pulse is generated by a different front-end seed source, thereby allowing the time and frequency domain characteristics of each beam to be independently controlled.

[0026] Furthermore, the seed laser source can be tuned to the center wavelength.

[0027] Furthermore, the time 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 control accuracy at the picosecond level.

[0028] Furthermore, the phase modulation unit can achieve control over the spectrum.

[0029] Furthermore, by combining the spectral dispersion grating with the phase modulation unit in the front-end seed source, a speckle structure that varies over time can be obtained, thereby smoothing the focal spot within a specific time period.

[0030] Furthermore, the target focal spot size of the continuous phase plate used in the transmission 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 high-energy driven main pulses, the target focal spot size is slightly smaller than the radius R. b The target surface is designed to reduce energy transfer in the cross beams and improve beam-target coupling efficiency.

[0031] Furthermore, the polarization state of the polarization control plate can be linearly polarized light along the tangent or normal direction of the beam ring for different nanosecond laser pulses, or it can be left-handed or right-handed circularly polarized light, or elliptically polarized light, in order to reduce the correlation between the sub-beams.

[0032] Furthermore, the target positions of the m-beam low-energy main pulse and the (nm)-beam high-energy driving main pulse are different, with the target position of the (nm)-beam high-energy driving main pulse being slightly further back.

[0033] The advantages of this invention are as follows:

[0034] 1. This invention proposes for the first time a nanosecond laser timing control method based on a dual-cone collision direct-drive laser device. By using a minority of the beams to generate low-energy main pulses and focusing them on a target surface with an initial radius, better illumination uniformity is provided. The remaining majority of the beams generate high-energy driving main pulses and focus them on a relatively small target surface to reduce energy transfer of the cross beams and improve beam-target coupling efficiency.

[0035] 2. The zoom control described in this invention is achieved by generating low-energy foot pulses using a few beams, which reduces the impact of electrical noise in the front-end system on waveform stability under low power conditions. At the same time, it increases the gain saturation of the main amplification link, thereby improving the overall stability and control accuracy of the foot pulses. This effectively improves the control accuracy of the time-power curve irradiated onto the target surface, and better controls the timing and intensity of the shock wave. Attached Figure Description

[0036] Figure 1 (a) is the reference time-power curve of the biconical collision direct-drive laser device described in this invention. Figure 1 (b) The time-power curves of a single foot pulse and a single driving main pulse after using the zoom scheme of "4 foot pulses + 12 main pulses".

[0037] Figure 2 This shows the beam arrangement on a single cone of the dual-cone collision direct-drive laser device in this invention.

[0038] Figure 3 This is the optical path diagram of each nanosecond laser pulse during transmission in the biconical collision direct-drive laser device of the present invention.

[0039] Figure 4 This paper presents the variation of the irradiation uniformity of the four foot pulses and twelve main pulses on the target surface with the integration time in the dual-cone collision direct-drive laser device of this invention.

[0040] Figure 5 The images show the irradiation results of the dual-cone collision direct-drive laser device in this invention on the target surface with an integration time of 100 ps. Among them, (a) shows the irradiation results of 4 foot pulses on the target surface with an initial target radius, and (b) shows the irradiation results of 12 driving main pulses on the target surface with an initial target radius of 0.7 times.

[0041] Figure 6 The time-power curves of a single foot pulse and a single driving main pulse after the zoom scheme of "2 foot pulses + 14 main pulses" is shown in the biconical collision direct-drive laser device of the present invention.

[0042] Figure 7The images show the irradiation results of the dual-cone collision direct-drive laser device in this invention on the target surface at an integration time of 100 ps. Among them, (a) shows the irradiation results of 2 foot pulses on the target surface with an initial target radius, and (b) shows the irradiation results of 14 driving main pulses on the target surface with an initial target radius of 0.7 times.

[0043] 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 source laser; 12-time pulse shaping unit; 13-phase modulation unit. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments described herein are only for further description of the present invention and do not imply any limitation on the scope of protection of the present invention.

[0045] Example 1:

[0046] This embodiment primarily considers the physical requirement for target compression in the biconical collision direct-drive laser device described in this invention, providing the physical basis for the "4 foot pulses + 12 main pulses" zoom scheme design based on the biconical collision direct-drive laser device, with a beam aperture of 375mm × 375mm. The biconical collision direct-drive laser device requires a reference time-power curve irradiated onto a single cone as shown in the figure. Figure 1 As shown in (a), when evenly distributed across 16 nanosecond laser pulses, the contrast of the reference time-power curve on a single path is 55:1, and the highest peak power density on a single path is 711 MW / cm². 2 The energy density is 2.97 J / cm³. 2 .

[0047] To improve the control accuracy of the foot pulses and maximize the utilization of the device's output capacity, it is considered that four of the beams are used to generate foot pulses with a duration of 0–10 ns and a total energy of 6.20 kJ, while the remaining 12 beams are used to generate driving main pulses with a duration of 10–15 ns and a total energy of 60.54 kJ. This ensures that the sum of these 16 nanosecond laser pulses satisfies the reference time-power curve irradiated onto the single cone.

[0048] Thus, the contrast ratio of a single foot pulse is 13:1, and the highest peak power density allocated to a single foot pulse is 666 MW / cm². 2 The energy density of a single-channel foot pulse is 1.16 J / cm². 2 The contrast ratio of the single-path drive main pulse is 3.7:1, and the highest peak power density allocated to the single-path drive main pulse is 948 MW / cm².2 The energy density of the single-channel drive main pulse is 3.57 J / cm². 2 The time-power curves of a single-channel foot pulse and a single-channel drive main pulse are as follows: Figure 1 As shown in (b), compared to the single-channel reference time-power curve, the waveform contrast is significantly reduced, thereby effectively improving the stability of the pulse.

[0049] Since the 12 main driving pulses begin to occur 10ns after the other 4 foot pulses, the 12 main driving pulses use a small focal spot CPP, while the other 4 foot pulses use a large focal spot CPP, thus realizing the zoom technology solution.

[0050] Please see Figure 2 , Figure 2 This shows the beam arrangement on a single cone of a laser device based on direct-drive dual-cone collision.

[0051] Please see Figure 3 First, consider the irradiation uniformity of the four foot pulses on the large focal spot in the far field. The angle between these four foot pulses and the polar axis is 26°. Each foot pulse passes through the front 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 during generation, transmission and focusing.

[0052] 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.

[0053] The target focal spot of the continuous phase plate 5 is an elliptical focal spot, which is projected onto the target surface as a circular focal spot with a radius of slightly less than 1000um.

[0054] The focal length of the focusing lens 7 is 5m; the initial radius R of the target surface 8 is... t =1000um, the fundamental center wavelength of each foot pulse is 1053nm, the third harmonic center wavelength is 351nm, and the landing point accuracy is 30um rms.

[0055] To quantitatively analyze the change in focal spot uniformity with integration time, the luminous flux contrast ratio (C) of the focal spot is used for evaluation. The smaller the luminous flux contrast ratio, the better the focal spot uniformity. The calculation method of C is expressed as follows:

[0056]

[0057] In the formula, I i,j (x f ,y f ) is on the focal plane (x)f ,y f The light intensity at position I mean (x f ,y f ) represents the average light intensity on the focal plane.

[0058] When quantitatively analyzing the uniformity of the focal spot, the luminous flux contrast of the focal spot was calculated for the region with an 80% circumferential energy ratio. The results are as follows: Figure 4 As shown, Figure 4 (a) shows the variation of the irradiance uniformity of the four foot pulses on the target surface 8 with the integration time. At an integration time of 100 ps, ​​the irradiance uniformity is 0.1740. The irradiance on the target surface is as follows: Figure 5 As shown in (a).

[0059] Similarly, consider the irradiation of the small focal spot by 12 driving main pulses, which include 4 pulses with an angle of 32° to the polar axis and 8 pulses with an angle of 45° to the polar axis.

[0060] For these 12 driving main pulses, the radius of the target surface 8 is 0.7R. t The change in luminous flux contrast of the focal spot within its 80% encircling energy ratio region with integration time is as follows: Figure 4 As shown in (b), with an integration time of 100 ps, ​​the irradiation uniformity is 0.2072, and the irradiation pattern on the target surface is as follows. Figure 5 As shown in (b).

[0061] Example 2:

[0062] This embodiment primarily considers the physical basis of the zoom scheme design based on a dual-cone collision direct-drive laser device, consisting of "2 foot pulses + 14 main pulses," with a beam aperture of 375mm × 375mm. The time-power curves of the single-path foot pulse and single-path main drive pulse obtained through this division are shown below. Figure 6 As shown.

[0063] Thus, the highest peak power density allocated to a single foot pulse is 1332 MW / cm². 2 The energy density of a single-channel foot pulse is 2.32 J / cm². 2 The highest peak power density allocated to a single drive main pulse is 812 MW / cm². 2 The energy density of the single-channel drive main pulse is 3.06 J / cm². 2 .

[0064] Furthermore, in this zoom scheme, two adjacent foot pulses from the four foot pulses described in Example 1 are selected as the two foot pulses in Example 2, and applied to R. tOn the target surface, the uniformity of the focal spot was then quantitatively analyzed. At an integration time of 100 ps, ​​the luminous flux contrast was calculated for the focal spot region with an 80% circumferential energy ratio, yielding a result of 0.1157. The irradiation conditions on the target surface are as follows: Figure 7 As shown in (a).

[0065] Similarly, considering 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 within the region of 80% of the circumferential energy ratio is 0.2117. The irradiation conditions on the target surface are as follows: Figure 7 As shown in (b).

[0066] Compared to Example 1, although Example 2 uses two foot pulses to achieve better irradiation uniformity on the large focal spot (because the polarization directions of the two beams can be controlled to be perpendicular to each other, which is equivalent to incoherent superposition on the target surface), the peak power density of a single foot pulse in Example 2 is too high, which can easily damage the optical components.

[0067] The above-described embodiments are merely preferred embodiments of the present invention and are not limited to the present invention; various modifications and variations can be made to the present invention by those skilled in the art.

Claims

1. A nanosecond laser timing and control method based on a biconical collision direct-drive laser device, characterized in that, The time waveforms of all nanosecond laser pulses in the biconical collision direct-drive laser device are redistributed under the condition of satisfying the near-isentropic compression waveform that drives implosion, including: A small portion of the beam is used to generate a low-energy foot pulse, which is focused on a large target surface. Under the action of the low-energy foot pulse, the target surface slowly contracts inward, and at the end of the duration of the low-energy foot pulse, it contracts into a smaller target surface. The remaining majority of the beam is used to generate a driving main pulse, which is then focused onto this smaller target surface, thereby achieving zoom.

2. The nanosecond laser timing and control method based on a biconical 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–τ, and the duration of the low-energy foot pulse is 0–t. d The duration of the driving main pulse is t. d ~τ,t d This corresponds to the target pellet starting from its initial radius R. t Converging to 0.7R t The time corresponding to the time.

3. The nanosecond laser timing and control method based on a biconical collision direct-drive laser device according to claim 1, characterized in that, In the biconical collision direct-drive laser device, there are n nanosecond laser pulses. To ensure the intensity balance of the sum of the power of n / 2 nanosecond laser pulses on the upper and lower conical surfaces, the time waveform of each laser pulse is redesigned so that the sum of n / 2 nanosecond laser pulses satisfies the near-isentropic compression waveform for driving implosion.

4. The nanosecond laser timing and control method based on a biconical collision direct-drive laser device according to claim 3, characterized in that, For an n / 2 nanosecond laser pulse on a single cone, a low-energy pulse is generated by utilizing m of the beams, i.e., a small portion of the beam, and focused onto a relatively large target surface 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, with an initial radius R. t The target surface slowly contracts inward, when at t d At time R, the target surface converges to a target surface radius of R. b When the target surface is relatively small, R b / R t =0.7, the remaining (n / 2-m) beam, i.e., the high-energy driving main pulse generated by the remaining majority of the beam, is focused on a radius of R. b Zooming is achieved on the target surface.

5. The nanosecond laser timing and control method based on a biconical collision direct-drive laser device according to claim 4, characterized in that, The m-beam nanosecond laser pulses that generate low-energy full pulses should meet the following conditions: - Each nanosecond laser pulse is at a safe energy density of 4 J / cm² 2 Inside; - The load of m-beam nanosecond laser pulses that generate low-energy main pulses is comparable to that of (n / 2-m)-beam nanosecond laser pulses that generate high-energy driving main pulses; -m beams generate low-energy, full-pulse nanosecond laser pulses, which are arranged as close as possible to the ring with the smallest angle to the polar axis, in order to maximize the irradiation uniformity of the driving laser on the target surface in the early stages.

6. An apparatus for implementing the nanosecond laser timing and scalability control method based on a biconical collision direct-drive laser device as described in any one of claims 1-5, characterized in that, The system includes 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) arranged sequentially along the transmission direction of the front-end seed source (1). The seed light output from the front-end seed source (1) enters the transmission amplification component (3) after passing through the spectral dispersion grating (2) to amplify the beam aperture and energy. After the frequency doubling crystal (4) converts the fundamental frequency light into third harmonic light, the continuous phase plate (5) shapes the far-field focal spot into a focal spot with a certain shape and size. After passing through the polarization control plate (6), the focusing lens (7) focuses the shaped focal spot onto the far-field target surface (8).

7. The apparatus 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 apparatus according to claim 6, characterized in that, The front-end seed source (1) includes a seed source laser (11), a time pulse shaping unit (12), and a phase modulation unit (13) arranged sequentially on the same optical axis; The seed light source laser (11) is used to tune the center wavelength; The time pulse shaping unit (12) is used for precise control of 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 control precision at the picosecond level. The phase modulation unit (13) is used to control the spectrum.

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

10. The apparatus according to claim 8, characterized in that, The target focal spot size of the continuous phase plate (5) used during the transmission 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 optimized to provide better illumination uniformity; for high-energy driven main pulses, the target focal spot size is slightly smaller than that with a radius of R. b The target surface is designed to reduce energy transfer in the cross beams and improve beam-target coupling efficiency.

11. The apparatus according to claim 8, characterized in that, The polarization state of the polarization control plate (6) can be linearly polarized light along the tangent or normal direction of the position on the ring where the beam is located, or it can be left-handed or right-handed circularly polarized light, or it can be elliptical polarized light, which reduces the correlation between the sub-beams.

12. The apparatus according to claim 8, characterized in that, The target surface (8) positions of the m-beam low-energy foot pulse and the (nm)-beam high-energy driving main pulse are different, with the target surface (8) position of the (nm)-beam high-energy driving main pulse being slightly further back.

Images