A laser driving device and a method for obtaining a uniform light field

Abstract

The present invention provides a laser driving device and a method for obtaining a uniform light field. The laser driving device is a high laser driving device for laser fusion level that obtains a uniform light field based on narrowband low-spatial-coherence light. The narrowband low-spatial-coherence light serves as the seed source of the laser driving device, the amplification and transmission unit amplifies the seed source, the frequency conversion unit realizes laser frequency conversion, and the focusing component is used for laser focusing and uniform illumination. The present invention improves the uniformity of the output light field of the laser driving device, solves the problem of low second harmonic generation efficiency caused by the wide spectral band technical solution and reduces the problem of optical element damage caused by self-focusing, breaks through the energy limitation caused by the limited load of ultraviolet elements, improves the overall output energy of the laser driving device, and further improves the overall efficiency of the laser device.

Description

Technical Field

[0001] The invention relates to the field of lasers, and in particular to a laser driving device for laser fusion research and a method for obtaining a uniform light field. Background Art

[0002] In a high-power laser inertial confinement fusion driver, the non-uniform light field irradiates the target surface, which will cause fluid instability and laser-plasma interaction instability during the implosion process, resulting in experimental failure. At present, the main method used is to solve the problem of non-uniform light field by combining spatial beam smoothing technology and temporal beam smoothing technology, but the uniformity still cannot meet the experimental requirements. There are also schemes that use broadband light sources for beam smoothing, but efficient amplification and frequency conversion efficiency cannot be achieved. In addition, in current laser drive devices, the phase disturbance caused by the spatial coherence of the laser during transmission amplification will lead to nonlinear self-focusing, causing damage to optical devices, thereby limiting the load capacity of the laser driver. Therefore, around a high-power laser device with low spatial coherence, the present invention can not only further improve the energy of the laser output, but also achieve uniform irradiation in a physical laboratory. Summary of the invention

[0003] The current laser driving device has phase disturbance and poor light field uniformity, which leads to self-focusing and component damage, thus limiting the laser output. In the current solution, high-efficiency and high-energy output cannot be achieved by using wide spectral band technology; the uniformity still cannot meet the experimental requirements by combining spatial beam smoothing technology with temporal beam smoothing technology. In order to solve the above problems, the present invention proposes a laser driving device based on a narrowband low spatial coherence light source.

[0004] The reason why the spatial beam smoothing technology needs the cooperation of the time domain beam smoothing technology is that the incident light field is a highly coherent light field in space, and the sub-beams divided by the spatial beam smoothing module are also coherent, thus generating a high-frequency modulated light field. The spatial distribution of the speckles in the high-frequency modulated light field remains unchanged during the entire pulse duration, which is not conducive to the implosion. The time domain smoothing technology increases the number of independent speckles within the coherent time, thereby smoothing out the inhomogeneity of the high-order modes in the integral effect over the entire time range. However, the time domain beam smoothing technology can only eliminate part of the high-frequency information, so the uniformity of the light field cannot currently meet the experimental requirements.

[0005] The inventor found that there is no problem with the technical solution of combining spatial beam smoothing and temporal beam smoothing. The essential reason is that this solution regulates a spatially highly coherent optical field, and there is still local modulation in a specific spatial and temporal domain. It just appears as a uniform distribution during the integration process over the entire temporal domain. Therefore, the present invention proposes a laser driver that uses light from a narrowband and low-spatial-coherence light source as the seed source. In this way, a low-spatial-coherence laser optical field is obtained after amplification, solving the problem that the irradiance uniformity of the optical field does not change with time and space.

[0006] In the present invention, during the process of transmission and amplification of the low-coherence light, various damages caused by interference modulation in current laser devices, such as those, will be greatly reduced, thereby improving the load capacity of the laser driving device. Since the current second-harmonic generation and third-harmonic generation crystals have relatively small matching angles, the broadband frequency conversion efficiency is poor. Therefore, the present invention proposes that it is necessary to not only meet the characteristics of low spatial coherence but also meet the narrowband characteristics. The present invention narrows the fluorescence spectrum of the gain medium through the threshold adjustment of the laser cavity and the gain narrowing effect of the laser gain medium, making it meet the frequency conversion matching angle, obtaining a high frequency conversion efficiency, and thus improving the efficiency of the entire laser driver.

[0007] The specific technical solution of the present invention is as follows:

[0008] A laser driving device uses a narrowband and low-spatial-coherence light source as the seed source for efficient amplification transmission and frequency conversion, and finally realizes uniform irradiation of the target surface.

[0009] A laser driving device includes: a laser seed source (1), an amplification transmission unit (2), a frequency conversion unit (3), and a focusing unit (4); the laser seed light source (1) is a narrowband and low-spatial-coherence light source for generating narrowband and low-spatial-coherence laser light; the amplification transmission unit (2) is used for the amplification and transmission of the laser; the frequency conversion unit (3) is used for the transformation of the laser frequency; the focusing unit (4) is used to achieve laser focusing; the laser seed light source (1) generates narrowband and low-spatial-coherence light, which is amplified by the amplification transmission unit (2), and the amplified light is then frequency-converted by the frequency conversion unit (3), and the frequency-converted light is focused by the focusing unit (4).

[0010] The laser seed source (1) is a low-spatial-coherence light source with a bandwidth not exceeding For example, during the third-harmonic generation process of a KDP crystal, in the case of type-II phase matching, if the bandwidth is a third-harmonic conversion efficiency as high as 60 - 70% can be guaranteed; if the bandwidth increases to the conversion efficiency is 50 - 60%, and compared with the bandwidth the third-harmonic conversion efficiency drops by 15%.

[0011] The laser seed source (1) is a low spatial coherence light source, that is, according to the van Cittert-Zernike theorem, the modulus of the complex spatial coherence degree of the laser light field is less than 1, and more preferably less than 0.5.

[0012] The amplification and transmission unit (2) has the function of laser amplification and transmission. The amplification unit includes one or more amplification gain media; the shape of the amplification gain medium can be rod-shaped, sheet-shaped, etc.; the laser can pass through the same amplification gain medium once or multiple times to obtain the required gain amplification.

[0013] The amplification and transmission unit (2) further includes a spatial transmission device for controlling the beam divergence angle, which can realize the transmission regulation of the laser beam.

[0014] The amplification and transmission unit (2) further includes a spatial filter. The spatial filter of the present invention can simplify the traditional spatial filter, making the structure of the amplification and transmission unit (2) simpler.

[0015] The frequency conversion performed by the frequency conversion unit (3) can be second harmonic generation, or third harmonic generation or fourth harmonic generation.

[0016] The focusing unit (4) includes an optical element for focusing.

[0017] The optical element for focusing is one of an aspherical lens, a reflective focusing mirror, and a wedge-shaped focusing lens.

[0018] The focusing unit (4) may further include an array lens or an array of orthogonal cylindrical lenses.

[0019] The focusing unit (4) may further include an optical element for adjusting the phase.

[0020] The optical element for adjusting the phase is a deformable mirror.

[0021] The laser driving device may further include a beam shaping component (6).

[0022] The beam shaping component (6) is used to control the beam intensity and phase.

[0023] The beam shaping component (6) is one or several of a serrated aperture, a combination of a birefringent lens group and a neutral density filter, an amplitude-type (or phase-type) binary optical panel, a binary transmittance liquid crystal cell, an amplitude-type electrically addressed modulator, an amplitude-type optically addressed modulator, a phase-type electrically addressed spatial light modulator, and an adaptive optical component.

[0024] The laser driving device may further include a measurement unit (7).

[0025] The measurement unit (7) is used to measure various signals in the laser driving device.

[0026] The laser driving device may further include a collimation component (8).

[0027] The collimation component (8) is used to collimate each light beam in the laser driving device.

[0028] The laser driving device may further include a control component (9).

[0029] The control component (9) is used to control various signals in the laser driving device.

[0030] The present invention also provides a method for obtaining a uniform focused light spot: using a narrow-band low spatial coherence light source as the laser seed source (1), which is amplified by the amplification and transmission unit (2), the amplified light is then frequency-converted by the frequency conversion unit (3), and the frequency-converted light is focused by the focusing unit (4) to obtain a light spot that is uniform in both the near and far fields.

[0031] Compared with the prior art, the laser driving device based on narrow-band low spatial coherence light provided by the present invention can effectively solve the three major bottleneck problems of power energy, ultraviolet load, and irradiation uniformity existing in current high-power laser devices:

[0032] (1) Solved the problem of uniform irradiation of the optical field, which is the most important in physical experiments;

[0033] (2) Overcame the problems of low efficiency in amplification and frequency conversion caused by using a broadband light source;

[0034] (3) Solved the problem of filament damage of optical elements caused by nonlinear effects in the laser driving device.

[0035] In addition, the present invention has the characteristics of simple structure, convenient adjustment, high efficiency, easy implementation, and strong practicability. The device can be simplified on the original basis. For example, the original spatial and temporal beam smoothing components can be reduced, and functions such as spatial filtering can be simplified. It provides a brand-new laser driver for laser fusion and helps with direct and indirect drive fusion ignition. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0037] Figure 1 : Schematic diagram of the simple structure of the present invention

[0038] Figure 2(a): Spatial filter structure in the amplification and transmission unit (2) of the laser driving device in the present invention

[0039] Figure 2(b): Spatial filter structure in the amplification and transmission unit (2) of a conventional laser driving device

[0040] Figure 3(a): Frequency conversion unit (3) (third harmonic frequency conversion) of the laser driving device in the present invention

[0041] Figure 3(b): Frequency conversion unit (3) (third harmonic frequency conversion) of a conventional laser driving device

[0042] Figure 4 : Focusing unit (4) of the laser driving device in the present invention

[0043] Figure 5 : Light field diagrams (a) near field (b) far field after amplification, transmission, and frequency conversion obtained by the present invention

[0044] Figure 6 : Frequency conversion unit (3) (fourth harmonic frequency conversion) of the laser driving device in the present invention

[0045] Figure 7 : Focusing unit (4) of the laser driving device in the present invention

[0046] Figure 8 : Focusing unit (4) of the laser driving device in the present invention

[0047] Figure 9 : Focusing unit (4) of the laser driving device in the present invention

[0048] Figure 10 : Schematic structural diagram of a laser driving device including a collimation assembly (8), a measurement unit (7), and a control assembly (9)

[0049] Figure 11 : Schematic structural diagram of a laser driving device including a beam shaping assembly

[0050] Figure 12 : Schematic structural diagram of a laser driving device including a beam shaping assembly

[0051] Figure 13 : Spatial transmission device in the amplification and transmission unit (2) of the laser driving device in the present invention

[0052] Legend description

[0053] 1: Laser seed source; 2: Amplification and transmission unit; 3: Frequency conversion unit; 4: Focusing unit; 5: Target

[0054] 6: Beam shaping component; 7: Measuring unit; 8: Collimating component; 9: Control component;

[0055] 202: Spatial filter; 201: Preamplification stage; 203: Post-amplification stage; 2021: First beam expander lens; 2022: Spatial filtering small hole; 2023: Second beam expander lens, 204: Simplified spatial filter; 205: Quarter-wave plate; 206: Rod-shaped amplification gain medium laser head; 207: First polarization beam splitter prism; 208: Intra-cavity spatial filter; 209: First reflector; 210: Second polarization beam splitter prism; 211: Spatial transmission filter; 212: Faraday rotator; 213: Second reflector; 214: Beam expander; 215: First sheet-shaped amplification gain medium laser head; 216: First spatial filter; 217: Second sheet-shaped amplification gain medium laser head; 218: Polarization emission mirror; 219: First total reflector; 220: Second total reflector; 221: Second spatial filter; 222: Spatial transmission device; 2221: First lens; 2222: Second lens;

[0056] 30: Fundamental frequency random phase plate; 31: Vacuum window; 32: Second harmonic generation crystal; 33: Third harmonic generation crystal; 34: Second harmonic generation random phase plate; 35: Fourth harmonic generation crystal;

[0057] 41: Aspherical lens; 42: Wedge-shaped focusing lens; 43: Deformable mirror; 44: Array lens; 45: Beam deflection mirror group; 46: Reflective focusing mirror;

[0058] 61: Deformable mirror; 62: Sawtooth aperture. Detailed implementation mode

[0059] To enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. The following further illustrates and describes the present invention in conjunction with the specification drawings and preferred specific embodiments, but does not limit the protection scope of the present invention accordingly.

[0060] Embodiment 1:

[0061] This embodiment is a laser driving device, as Figure 1 shown, the laser driving device includes: a laser seed source (1), an amplification and transmission unit (2), a frequency conversion unit (3), a focusing unit (4), and a target (5). The laser seed source (1) is narrowband low-spatial coherence light, with a bandwidth The coherent light is amplified and transmitted through the amplification and transmission unit (2), and then frequency-converted through the frequency conversion unit (3). The light after frequency conversion by the frequency conversion unit is focused through the focusing unit (4), and finally irradiates the target (5).

[0062] In this embodiment, the amplification and transmission unit (2), as shown in Fig. 2(a), includes a pre-amplification stage (201), a post-amplification stage (203), and a simplified spatial filter (204); the simplified spatial filter (204) includes a beam expander lens 2021 and a beam expander lens 2023. In a conventional amplification and transmission device (as shown in Fig. 2(b)), the spatial filter (202) includes not only the beam expander lens 2021 and the beam expander lens 2023, but also a spatial filtering small hole 2022. In the present invention, the spatial filtering small hole can be omitted from the spatial filter, and this simplification reduces the debugging difficulty of the laser device and improves the target shooting efficiency of the laser device.

[0063] In this embodiment, the frequency conversion unit (3), as shown in Fig. 3(a), is triple-frequency amplification, and specifically includes a vacuum window (31), a frequency doubling crystal (32), and a triple-frequency crystal (33). In a conventional frequency conversion unit (as shown in Fig. 3(b)), a fundamental frequency random phase plate (30) and a second harmonic random phase plate (34) are further included. In the present invention, the fundamental frequency random phase plate (30) and the second harmonic random phase plate (34) are simplified, the mechanism is simpler, and the debugging difficulty of the laser device is reduced.

[0064] In this embodiment, the focusing unit (4), as Figure 4 shown, the focusing lens is an aspherical lens (41).

[0065] Figure 5 are the near-field (a) and far-field output diagrams (b) of the laser driving device based on low spatial coherence light in this implementation scheme.

[0066] Embodiment Two:

[0067] In this embodiment, the frequency conversion unit (3), as Figure 6 shown, is quadruple-frequency amplification, and specifically includes a vacuum window (31), a frequency doubling crystal (32), a triple-frequency crystal (33), and a quadruple-frequency crystal (35).

[0068] In this embodiment, the focusing unit (4), as Figure 7 shown, the focusing lens is a wedge-shaped focusing lens (42).

[0069] Embodiment Three:

[0070] As Figure 8 shown, in this embodiment, the focusing unit (4) includes a deformable mirror (43), a beam deflection mirror group (45), and a reflective focusing mirror (46).

[0071] Embodiment Four:

[0072] As Figure 9As shown in the figure, in this embodiment, the focusing unit (4) includes a deformable mirror (43), an array lens (44), and an aspherical lens (41).

[0073] Embodiment Five:

[0074] Embodiment Five is based on Embodiment One, with a collimating component 8, a measuring unit 7, and a control component 9 added, as Figure 10 shown. The collimating component 8 collimates each beam in the laser driving device; the measuring unit 7 measures various signals in the laser driving device; the control component 8 controls various signals in the laser driving device. The collimating component 8, the measuring component 7, and the control component 9 can assist the laser driving device to complete target shooting efficiently and with high quality.

[0075] Embodiment Six:

[0076] This embodiment is based on Embodiment One, and a beam shaping component (6) is incorporated in the beam amplification and transmission unit (2), as Figure 11 shown. The beam shaping component (6) effectively controls the beam intensity and phase, including a deformable mirror (61) and a serrated aperture (62). The amplification and transmission unit (2) includes a quarter-wave plate (205), a rod-shaped amplification gain medium laser head (206), a first polarization beam splitter prism (207), an intracavity spatial filter (208), a first mirror (209), a second polarization beam splitter prism (210), a spatial transmission filter (211), a Faraday rotator (212), a second mirror (213), and a beam expander (214).

[0077] Embodiment Seven:

[0078] This embodiment is based on Embodiment One, and a beam shaping component (6) is incorporated in the beam amplification and transmission unit (2), as Figure 12 shown. The beam shaping component (6) includes a deformable mirror (61). The amplification and transmission unit (2) includes a first sheet-shaped amplification gain medium laser head (215), a first spatial filter (216); a second sheet-shaped amplification gain medium laser head (217); a polarization emission mirror (218); a first total reflection mirror (219); a second total reflection mirror (220), and a second spatial filter (221).

[0079] Embodiment Eight:

[0080] In this embodiment, the spatial transmission device (222) in the amplification and transmission unit (2), as Figure 13 shown, includes a first lens (2221) and a second lens (2222). The spatial transmission device (222) is placed after the laser seed source (1) and before the spatial filter, and compresses the laser divergence angle.

Claims

1. A laser driving device, characterized in that Comprising: A laser seed source (1), an amplification and transmission unit (2), a frequency conversion unit (3), and a focusing unit (4); the laser seed source (1) is a narrow-band and low-spatial-coherence light source with a bandwidth not exceeding 5 Å, and is used to generate narrow-band and low-spatial-coherence laser light; The amplification and transmission unit (2) is used for amplifying and transmitting the laser. Among them, the amplification and transmission unit (2) includes one or more amplification gain media, and the amplification gain media are rod-shaped or sheet-shaped; The frequency conversion unit (3) is used for laser frequency conversion; the focusing unit (4) is used for laser focusing; the laser seed source (1) generates narrow-band and low-spatial-coherence light, and this narrow-band and low-spatial-coherence light is amplified by the amplification and transmission unit (2), and the amplified light is then frequency-converted by the frequency conversion unit (3), and the frequency-converted light is focused by the focusing unit (4).

2. The laser driving device according to claim 1, characterized in that, The modulus of the complex spatial coherence degree of the laser light field of the laser seed source (1) is less than 0.

5.

3. The laser driving device according to claim 1, characterized in that, The amplification and transmission unit (2) includes a spatial transmission device (222), which is used to control the beam divergence angle and realize the transmission regulation of the laser beam. Among them, the spatial transmission device (222) is placed after the laser seed source (1) and before the spatial filter.

4. The laser driving device according to claim 1, characterized in that, The frequency conversion performed by the frequency conversion unit (3) is second harmonic generation, or third harmonic generation, or fourth harmonic generation.

5. The laser driving device according to claim 1, characterized in that, The focusing unit (4) includes an optical element that plays a focusing role.

6. The laser driving device according to claim 1, characterized in that, The focusing unit (4) further includes an array lens or an array of orthogonal cylindrical lenses.

7. The laser driving device according to claim 1, characterized in that, The focusing unit (4) further includes an optical element that plays a role in adjusting the phase.

8. The laser driving device according to claim 1, characterized in that, Also comprising: A beam shaping component (6); the beam shaping component (6) is used to control the beam intensity and phase.

9. The laser driving device according to claim 8, characterized in that, The beam shaping component (6) is one or several of a serrated aperture, a combination of a birefringent lens group and a neutral density filter, an amplitude-type binary optical panel, a phase-type binary optical panel, a binary transmittance liquid crystal cell, an amplitude-type electrically addressable modulator, an amplitude-type optically addressable modulator, a phase-type electrically addressable spatial light modulator, and an adaptive optical component.

10. The laser driving device according to claim 1, characterized in that, Also comprising a collimation component (8), and the collimation component (8) is used to collimate each beam in the laser driving device.

11. A method for obtaining a uniform light field by using the laser driving device according to claim 1, characterized in that, It includes using a narrow-band and low-spatial-coherence light source as the laser seed source (1), the amplification and transmission unit (2) amplifies the light to obtain amplified light, the amplified light is then frequency-converted by the frequency conversion unit (3), and the focusing unit (4) focuses the frequency-converted light to obtain a light field that is uniform in both the near field and the far field.

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