A narrow pulse width laser with high repetition rate and high beam quality

Abstract

The present invention proposes a narrow-pulse laser with a high repetition rate and high beam quality. The laser comprises an electro-optical Q-switched resonant cavity, a first optical isolator, a double-pass amplification module, a first half-wave plate, a second optical isolator, and a beam quality optimization module, arranged in sequence. The centers of the electro-optical Q-switched resonant cavity, the first optical isolator, the double-pass amplification module, the first half-wave plate, the second optical isolator, and the beam quality optimization module are aligned on the same horizontal line. The present invention achieves high repetition rate, high beam quality, narrow-pulse laser pulse output, solving the problem of severe beam quality deterioration caused by thermal effects during the power amplification process of conventional lasers. This effectively improves work efficiency in fields such as lidar, laser processing, and optoelectronic countermeasures, achieving high peak power and high beam quality laser output.

Description

Technical Field

[0001] The present invention relates to the field of lasers, and in particular to a narrow pulse width laser with high repetition frequency and high beam quality. Background Art

[0002] With the rapid development of laser technology, demand for high-repetition-rate, high-beam-quality, narrow-pulse lasers is increasing in applications such as lidar, laser processing, and optoelectronic countermeasures. For example, lidar, which uses lasers as information carriers, is widely used in environmental monitoring, topography, and ocean mapping. Laser processing, which exploits the interaction between lasers and matter, offers significant advantages in cutting, welding, strengthening, and forming materials.

[0003] Light sources with high repetition rate and high beam quality can greatly improve the speed of laser radar scanning and data absorption, and can also improve the speed and efficiency of laser processing. Therefore, the development of narrow-pulse lasers with high repetition rate and high beam quality is the core driving force for the rapid development of laser radar, laser processing and other fields.

[0004] Generally speaking, the main means of achieving high-repetition-rate laser output are mode-locking technology and Q-switching technology. Although mode-locking technology can achieve pulse output with repetition rates as high as MHz or even GHz, its output energy is extremely low, usually on the order of ~nJ, and all of them are multi-longitudinal field modes, so it is rarely used in free space. Currently, the Q-switching technologies commonly used in mainstream all-solid-state lasers include electro-optical Q-switching, acousto-optical Q-switching, and passive Q-switching. Because the peak power of the ultrasonic oscillator is limited by the process of the acoustic wave generator, the output power of acousto-optical Q-switching is not high, and the pulse width is difficult to be less than 30ns. Passive Q-switching has the problems of low repeatability accuracy of the output laser pulse, wide pulse width, and low energy stability. Electro-optical Q-switching, thanks to its extremely high control accuracy, can simultaneously output high-repetition-rate narrow-pulse lasers.

[0005] Currently, common amplification technologies include CPA (chirped-pulse amplification), OPCPA (optical parametric chirped-pulse amplification), and MOPA (master oscillator power amplifier) plus SBS-PCM (stimulated Brillouin scattering phase conjugation mirror). CPA, an earlier amplification method, can easily achieve laser pulse output with peak powers of ~GW and pulse widths of ~ns. However, its limitations are significant, and the limited damage threshold of VBG (volume Bragg grating) has become a bottleneck in the development of this technology in recent years. In recent years, OPCPA has gradually replaced CPA as the mainstream amplification method, successfully overcoming the impact of the VBG damage threshold and achieving higher peak power laser output. However, this comes with challenges such as extremely high pump light quality requirements and phase matching between pump and signal light. As the most commonly used technology, MOPA is widely used in the development of high-energy all-solid-state lasers because its operation complexity is far lower than the above two technologies while still being able to achieve extremely high peak power laser output. The only drawback of this technology is the severe thermal effect during the amplification process, which can seriously deteriorate the output laser beam quality. Summary of the Invention

[0006] In response to the technical problems of low laser repetition frequency and deterioration of high-power laser beam quality, the present invention proposes a narrow-pulse laser with high repetition frequency and high beam quality, which solves the problem of serious deterioration of laser beam quality due to thermal effects.

[0007] In order to achieve the above-mentioned object, the technical solution of the present invention is implemented as follows: a narrow-pulse-width laser with high repetition rate and high beam quality, characterized in that: it includes an electro-optical Q-switched resonant cavity, a double-pass amplification module, a first half-wave plate and a beam quality optimization module arranged in sequence, and the center points of the electro-optical Q-switched resonant cavity, the double-pass amplification module, the first half-wave plate and the beam quality optimization module are on the same horizontal line; the electro-optical Q-switched resonant cavity generates high-repetition-rate linearly polarized seed light, the seed light enters the double-pass amplification module for power amplification, and then enters the beam quality optimization module to generate narrow-pulse-width laser pulses with high beam quality.

[0008] Furthermore, a first optical isolator is provided between the electro-optical Q-switched resonant cavity and the double-pass amplification module, and the center points of the electro-optical Q-switched resonant cavity, the first optical isolator and the double-pass amplification module are arranged on the same horizontal line; a second optical isolator is provided between the first half-wave plate and the beam quality optimization module, and the center points of the first half-wave plate, the second optical isolator and the beam quality optimization module are arranged on the same horizontal line; the first optical isolator and the second optical isolator are both composed of a polarizer, a Faraday rotator, and a half-wave plate arranged in sequence.

[0009] Furthermore, the electro-optical Q-switched resonant cavity includes a first 0° total reflection mirror, an electro-optical Q-switched switch, a first polarizer, a first LD side pump module and an output mirror arranged in sequence, and the center points of the first 0° total reflection mirror, the electro-optical Q-switched switch, the first polarizer, the first LD side pump module and the output mirror are on the same horizontal line. The seed light is output by the output mirror and enters the first optical isolator.

[0010] Furthermore, the dual-pass amplification module includes a second polarizer, a first single-pass amplifier, a first quarter-wave plate and a second 0° total reflection mirror, and the center points of the second polarizer, the first single-pass amplifier, the first quarter-wave plate and the second 0° total reflection mirror are on the same horizontal line; after the seed light passes through the first single-pass amplifier and the first quarter-wave plate, it is reflected by the second 0° total reflection mirror, and again passes through the first single-pass amplifier to achieve dual-pass amplification of the seed light, and finally outputs high-energy seed light at the second polarizer.

[0011] Furthermore, the beam quality optimization module includes a third polarizer, a second quarter wave plate, a first positive lens and a Brillouin medium pool, and the center points of the third polarizer, the second quarter wave plate, the first positive lens and the Brillouin medium pool are on the same horizontal line.

[0012] Furthermore, a first window mirror is provided on the opposite side of the Brillouin medium cell. The angle between the first window mirror and the horizontal direction is β, and the center of the first window mirror and the first positive lens are on the same horizontal line.

[0013] Furthermore, a second window mirror is provided on the opposite side of the Brillouin medium cell. The angle between the second window mirror and the horizontal direction is β1. The second window mirror and the center of the first positive lens are on the same horizontal line.

[0014] Furthermore, the second 0° total reflection mirror is coated with a total reflection film and forms an angle of 90° with the incident light to achieve total reflection of the seed light; the third polarizer is coated with an optical polarization film and the angle with the horizontal direction is the Brewster angle θ.

[0015] Furthermore, the end face of the Brillouin medium cell is cut with a specific inclination angle β, and the inclination angle β satisfies the following constraints:

[0016]

[0017] Among them, d1 is the height of the first positive lens; d2 is the distance between the center of the first positive lens and the incident point of the first window mirror; d3 is the distance between the upper end of the first positive lens and the upper end of the Brillouin medium cell; f is the focal length of the first positive lens.

[0018] Furthermore, the focal length f of the first positive lens should satisfy the following constraint conditions:

[0019]

[0020] Among them, d2 is the distance between the center of the first positive lens and the incident point of the first window mirror; L = cτ p / 2n, where L is the optimal interaction length between the seed light and the output Stokes light, L1 is the length of the Brillouin medium cell, L < L1, c is the speed of light, τ p is the pulse width of the pump light, n is the refractive index of the stimulated Brillouin scattering medium, D is the glass thickness of the first window mirror, and α' is the front surface refraction angle of the first window mirror.

[0021] The present invention adopting the above structure is simple in structure and good in stability, and can be used in advanced fields such as lidar, laser processing, and optoelectronic countermeasure. By using an electro-optic Q-switched resonator, it can achieve high-repetition-frequency and narrow-pulse-width laser output, making up for the deficiencies of mode-locking technology in low output energy, relatively wide pulse width of acousto-optic Q-switching, and low repetition frequency of passive Q-switching; by adopting the MOPA technology, it can generate high peak power, and combined with SBS-PCM, it solves the problem of serious deterioration of the beam quality introduced by the thermal effect during the power amplification process of traditional lasers. Brief Description of the Drawings

[0022] 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 use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 It is a schematic structural diagram of the present invention.

[0024] Figure 2 It is Figure 1 a schematic structural diagram of the electro-optic Q-switched resonator shown.

[0025] Figure 3 It is Figure 1 a schematic structural diagram of the double-pass amplification module shown.

[0026] Figure 4 It is Figure 1Schematic diagram of the structure of the beam quality optimization module shown.

[0027] Figure 5 for Figure 4 Schematic diagram of the Brillouin medium cell tilt angle shown.

[0028] Figure 6 for Figure 4 Schematic diagram of the optical path of the Brillouin medium cell window mirror.

[0029] In the figure, 1 is the electro-optical Q-switched resonant cavity, 2 is the first optical isolator, 3 is the double-pass amplifier module, 4 is the first half-wave plate, 5 is the second optical isolator, 6 is the beam quality optimization module, 1-1 is the first 0° total reflection mirror, 1-2 is the electro-optical Q-switched switch, 1-3 is the first polarizer, 1-4 is the first LD side pump module, 1-5 is the output mirror, 3-1 is the second polarizer, 3-2 is the first single-pass amplifier, 3-3 is the first quarter-wave plate, 3-4 is the second 0° total reflection mirror, 6-1 is the third polarizer, 6-2 is the second quarter-wave plate, 6-3 is the first positive lens, and 6-4 is the Brillouin medium pool, θ is the Brewster angle, α is the incident angle of the front surface of the first window mirror, β is the first tilt angle of the Brillouin medium pool, α1 is the incident angle of the front surface of the second window mirror in the Brillouin medium pool, β1 is the second tilt angle of the Brillouin medium pool, d1 is the height of the first positive lens, d2 is the distance between the center of the first positive lens and the incident point of the first window mirror, d3 is the distance between the upper end of the first positive lens and the upper end of the Brillouin medium pool, f is the focal length of the first positive lens, α′ is the refractive angle of the front surface of the first window mirror, α″ is the refractive angle of the back surface of the first window mirror, N1 is the refractive index of air, N2 is the refractive index of glass, N3 is the refractive index of medium, and D is the thickness of the first window mirror glass. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0031] like Figure 1As shown, a narrow-pulse laser with high repetition rate and high beam quality comprises an electro-optical Q-switched resonant cavity 1, a double-pass amplification module 3, a first half-wave plate 4, and a beam quality optimization module 6, which are arranged in sequence. The centers of the electro-optical Q-switched resonant cavity 1, the double-pass amplification module 3, the first half-wave plate 4, and the beam quality optimization module 6 are aligned on the same horizontal line. A first optical isolator 2 is disposed between the electro-optical Q-switched resonant cavity 1 and the double-pass amplification module 3, with the centers of the electro-optical Q-switched resonant cavity 1, the first optical isolator 2, and the double-pass amplification module 3 aligned on the same horizontal line. A second optical isolator 5 is disposed between the first half-wave plate 4 and the beam quality optimization module 6, with the centers of the first half-wave plate 4, the second optical isolator 5, and the beam quality optimization module 6 aligned on the same horizontal line. Both the first optical isolator 2 and the second optical isolator 5 are composed of a polarizer, a Faraday rotator, and a half-wave plate, which are arranged in sequence.

[0032] Among them, the main function of the electro-optical Q-switched resonant cavity 1 is to generate high repetition rate linearly polarized seed light, such as Figure 2 As shown, the electro-optical Q-resonant cavity 1 comprises a first 0° total reflection mirror 1-1, an electro-optical Q-switch 1-2, a first polarizer 1-3, a first LD side pump module 1-4, and an output mirror 1-5, arranged in sequence. The electro-optical Q-resonant cavity 1 utilizes the first 0° total reflection mirror 1-1 and the output mirror 1-5 to form a resonant cavity. By applying a voltage to the electro-optical crystal in the electro-optical Q-switch 1-2, combined with the action of the first polarizer 1-3, the electro-optical Q-resonant cavity 1 is placed in a high-loss state, thereby achieving reverse population accumulation. After the accumulation is complete, the applied voltage is removed, and the electro-optical Q-resonant cavity 1 continues to oscillate, extracting the energy accumulated by the first LD side pump module 1-4 during the high-loss state. Finally, high-repetition-rate linearly polarized seed light is output at the output mirror 1-5. The seed light is injected from the electro-optical Q-resonant cavity 1 into the first optical isolator 2. The first optical isolator 2 primarily blocks reverse-propagating light by utilizing the polarization principle, ensuring unidirectional transmission of the incident light and protecting the electro-optical Q-resonant cavity 1.

[0033] like Figure 3As shown, the dual-pass amplification module 3 mainly uses MOPA technology to generate high-peak power laser light. The dual-pass amplification module 3 includes a second polarizer 3-1, a first single-pass amplifier 3-2, a first quarter-wave plate 3-3, and a second 0° total reflection mirror 3-4. The center points of the second polarizer 3-1, the first single-pass amplifier 3-2, the first quarter-wave plate 3-3, and the second 0° total reflection mirror 3-4 are on the same horizontal line. Among them, the second polarizer 3-1 mainly outputs vertical linear polarized seed light; the first single-pass amplifier 3-2 is mainly used to amplify the passing light; the first quarter-wave plate 3-3 is used to change the polarization state of the seed light; the second 0° total reflection mirror 3-4 forms a 90° angle with the transmission direction of the seed light, and is coated with a total reflection film on the surface of the second 0° total reflection mirror to ensure total reflection of the incident laser light and reduce loss, thereby changing the optical path and reflecting all the incident light. After being emitted from the first optical isolator 2, the seed light is incident on the first single-pass amplifier 3-2 for the first amplification, and then passes through the first quarter-wave plate 3-3 and enters the second 0° total reflection mirror 3-4. The second 0° total reflection mirror 3-4 reflects all the incident seed light, so that the seed light passes through the first quarter-wave plate 3-3 and the first single-pass amplifier 3-2 again, realizing double-pass amplification of the seed light. Finally, the polarized high-energy laser output at the second polarizer 3-1 is input into the second optical isolator 5 through the first half-wave plate 4. The first half-wave plate 4 converts the polarization state of the high-energy laser into a horizontal polarization state to ensure that the high-energy laser can pass through the beam quality optimization module 6. The main function of the second optical isolator 5 is to ensure that the incident light passes through unidirectionally and protect the double-pass amplification module 3.

[0034] like Figure 4 As shown, the beam quality optimization module 6 includes a third polarizer 6-1, a second quarter wave plate 6-2, a first positive lens 6-3 and a Brillouin medium pool 6-4. The center points of the third polarizer 6-1, the second quarter wave plate 6-2, the first positive lens 6-3 and the Brillouin medium pool 6-4 are on the same horizontal line; a window mirror is provided on the opposite side of the Brillouin medium pool (6-4), and the center of the window mirror and the first positive lens 6-3 are on the same horizontal line. When the angle between the window mirror and the horizontal plane is β, it is the first window mirror, and when the angle between the window mirror and the horizontal plane is β1, it is the second window mirror.

[0035] Among them, the main function of the third polarizer 6-1 is to combine with the second quarter-wave plate 6-2 to change the polarization state of the laser to control the polarized output of the laser. The high-energy laser passes through the third polarizer 6-1 and the second quarter-wave plate 6-2 and then enters the first positive lens 6-3. The power density of the high-energy laser is increased by focusing through the first positive lens 6-3, and the electrostrictive effect is generated at the focal point to excite the acoustic wave field, generating Stokes light, and achieving the purpose of optimizing the beam quality through SBS-PCM; the main function of the Brillouin medium cell 6-4 is to generate stimulated Brillouin scattering, optimize the beam quality, and generate high-quality Stokes light output backward.

[0036] Specifically, the focal length of the first positive lens 6-3 should satisfy the following constraint conditions:

[0037]

[0038] Where d2 is the distance between the center of the first positive lens and the incident point of the first window mirror, L is the optimal interaction length between the high-energy laser and the output Stokes light, and satisfies the formula L = cτ p / 2n, L1 is the length of the Brillouin medium cell, and L < L1, c is the speed of light, τ p is the pulse width of the seed light after double-pass amplification, n is the refractive index of the stimulated Brillouin scattering medium, D is the thickness of the first window mirror glass, and α′ is the refraction angle of the front surface of the first window mirror.

[0039] As Figure 5 shown, the height of the first positive lens 6-3 is selected as d1, and the distance between the center of the first positive lens 6-3 and the incident point A of the first window mirror is d2. Select the extreme case where the reflected light of the Brillouin scattering medium window mirror just hits the lower edge of the first positive lens 6-3. At this time, the first tilt angle β of the Brillouin medium cell 6-4 can be obtained from the following expression:

[0040]

[0041] Select the second tilt angle β1 of the Brillouin medium cell <β, the laser incident point is B. At this time, the focal point of the first positive lens 6-3 is at point B of the front window mirror. At this time, the expression of the second tilt angle β1 of the Brillouin medium cell 6-4 is:

[0042]

[0043] Where d1 is the height of the first positive lens 6-3, d3 is the distance between the upper end of the first positive lens 6-3 and the upper end of the Brillouin medium cell 6-4, and f is the focal length of the first positive lens 6-3.

[0044] In order to reduce the impact of reflected light on the spatial energy distribution of the output Stokes light and avoid damage to the front window mirror due to laser focusing, the tilt angle β of the first window mirror should meet the following constraints:

[0045]

[0046] The included angle between the third polarizer 6 - 1 and the horizontal direction is the Brewster angle θ, which is used to output linearly polarized light with high beam quality.

[0047] like Figure 6 As shown, the incident light enters the first window mirror along the incident angle α, and the refraction angle α′ is generated by the optically rarer medium entering the optically denser medium, satisfying N1sinα=N2sinα′; the light emitted from the rear surface of the first window mirror enters the Brillouin medium pool 6-4 along the angle α″, and enters the optically rarer medium from the optically denser medium. The refraction angle α″ of the rear surface of the first window mirror satisfies N2sinα′=N3sinα″, and the angle between the incident light in the Brillouin medium pool 6-4 and the horizontal direction is (π / 2-β-α″).

[0048] After the incident light is refracted by the front surface of the first window mirror and enters the glass, it is reflected by the rear surface of the first window mirror and finally refracted out by the front surface. The incident index R and refractive index T of the front surface are:

[0049]

[0050]

[0051] Where N1 is the refractive index of air, and N2 is the refractive index of glass. Use R and T to calculate the loss incurred by the incident light entering the Brillouin medium cell through the window mirror, ensuring that the incident light is above the Brillouin scattering threshold and generating high-quality Stokes light.

[0052] In summary, the present invention proposes a narrow-pulse-width laser with high repetition rate and high beam quality. The electro-optical Q-switched resonant cavity generates high-repetition-rate linearly polarized light, and utilizes the MOPA+SBS-PCM amplification method to achieve high-repetition-rate, high-beam-quality narrow-pulse-width laser pulse output.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A narrow pulse width laser with high repetition rate and high beam quality, characterized by: The invention comprises an electro-optical Q-switched resonant cavity (1), a two-way amplification module (3), a first half-wave plate (4) and a beam quality optimization module (6) which are arranged in sequence, wherein the center points of the electro-optical Q-switched resonant cavity (1), the two-way amplification module (3), the first half-wave plate (4) and the beam quality optimization module (6) are on the same horizontal line; the electro-optical Q-switched resonant cavity (1) generates a high repetition rate linearly polarized seed light, the seed light enters the two-way amplification module (3) for power amplification, and then enters the beam quality optimization module (6) to generate a narrow pulse width laser pulse with high beam quality; The beam quality optimization module (6) comprises a third polarizer (6-1), a second quarter wave plate (6-2), a first positive lens (6-3) and a Brillouin medium pool (6-4), wherein the center points of the third polarizer (6-1), the second quarter wave plate (6-2), the first positive lens (6-3) and the Brillouin medium pool (6-4) are on the same horizontal line; A first window mirror is provided on the opposite side of the Brillouin medium pool (6-4), and the angle between the first window mirror and the horizontal direction is β , the centers of the first window mirror and the first positive lens (6-3) are on the same horizontal line; Tilt angle β The following constraints are met: Wherein, d1 is the height of the first positive lens (6-3); d2 is the distance between the center of the first positive lens (6-3) and the incident point of the first window mirror; and d3 is the distance between the upper end of the first positive lens (6-3) and the upper end of the Brillouin medium cell (6-4); f is the focal length of the first positive lens (6-3).

2. The high repetition rate, high beam quality, narrow pulse width laser according to claim 1, characterized in that: A first optical isolator (2) is provided between the electro-optical Q-switched resonant cavity (1) and the dual-pass amplification module (3), and the center points of the electro-optical Q-switched resonant cavity (1), the first optical isolator (2) and the dual-pass amplification module (3) are arranged on the same horizontal line; A second optical isolator (5) is provided between the first half-wave plate (4) and the beam quality optimization module (6), and the center points of the first half-wave plate (4), the second optical isolator (5) and the beam quality optimization module (6) are arranged on the same horizontal line; The first optical isolator (2) and the second optical isolator (5) are both composed of a polarizer, a Faraday rotator, and a half-wave plate which are arranged in sequence.

3. The high repetition rate, high beam quality, narrow pulse width laser according to claim 2, characterized in that: The electro-optical Q-switched resonant cavity (1) comprises a first 0° total reflection mirror (1-1), an electro-optical Q-switched switch (1-2), a first polarizer (1-3), a first LD side pump module (1-4) and an output mirror (1-5) which are arranged in sequence. The center points of the first 0° total reflection mirror (1-1), the electro-optical Q-switched switch (1-2), the first polarizer (1-3), the first LD side pump module (1-4) and the output mirror (1-5) are on the same horizontal line. The seed light is output by the output mirror (1-5) and enters the first optical isolator (2).

4. The high repetition rate, high beam quality, narrow pulse width laser according to claim 3, characterized in that: The double-pass amplification module (3) comprises a second polarizer (3-1), a first single-pass amplifier (3-2), a first quarter-wave plate (3-3) and a second 0° total reflection mirror (3-4); the center points of the second polarizer (3-1), the first single-pass amplifier (3-2), the first quarter-wave plate (3-3) and the second 0° total reflection mirror (3-4) are on the same horizontal line; after the seed light passes through the first single-pass amplifier (3-2) and the first quarter-wave plate (3-3), it is reflected by the second 0° total reflection mirror (3-4) and again passes through the first single-pass amplifier (3-2) to achieve double-pass amplification of the seed light, and finally outputs high-energy seed light at the second polarizer (3-1).

5. The high repetition rate, high beam quality, narrow pulse width laser according to any one of claims 1 to 4, characterized in that: A second window mirror is provided on the opposite side of the Brillouin medium pool (6-4), the angle between the second window mirror and the horizontal direction is β1, and the center of the second window mirror and the first positive lens (6-3) are on the same horizontal line.

6. The high repetition rate, high beam quality, narrow pulse width laser according to claim 4, characterized in that: The second 0° total reflection mirror (3-4) is coated with a total reflection film and has an angle of 90° with the incident light to achieve total reflection of the seed light; the third polarizer (6-1) is coated with an optical polarization film and has an angle of Brewster angle with the horizontal direction. θ .

7. The high repetition rate, high beam quality, narrow pulse width laser according to claim 6, characterized in that: The end face of the Brillouin medium cell (6-4) is inclined at an angle β Cutting.

8. The narrow pulse width laser with high repetition rate and high beam quality according to claim 7, characterized in that: The focal length of the first positive lens (6-3) f The following constraints should be met: in, d 2 is the distance between the center of the first positive lens (6-3) and the incident point of the first window mirror; ,in, L is the optimal interaction length between the seed light and the output Stokes light, 𝐿1 is the length of the Brillouin medium cell (6-4), 𝐿<𝐿1, c is the speed of light, 𝜏 p is the pump light pulse width, 𝑛 is the refractive index of the stimulated Brillouin scattering medium, D is the glass thickness of the first window mirror, is the refraction angle of the front surface of the first window mirror.

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