High-brightness green laser system using SBS phase conjugate mirror with cooling device

Abstract

The invention provides a high-brightness green laser system utilizing an SBS phase conjugate mirror with a cooling device, which comprises a seed light and isolation module, an SBS phase conjugate mirror module with a cooling device and a frequency doubling module which are arranged in sequence, the center of the seed light and isolation module and the center of the SBS phase conjugate mirror module with the cooling device are arranged on the same straight line, and the frequency multiplication module corresponds to the seed light and isolation module. After being output by the output end of the seed light and isolation module, the seed light enters the SBS phase conjugate mirror module with the cooling device, after peak power density is increased, reversely transmitted Stokes seed light is generated and transmitted to the output end of the seed light and isolation module again, and is reflected to the frequency doubling module by the output end of the seed light and isolation module; and after being amplified and split by the frequency doubling module, the laser is converted into high-brightness green laser to be output. The heat effect in the SBS-PCM is improved, SBS pulse output with high beam quality, high energy stability and high compression rate is achieved, and high-brightness green laser is achieved through external cavity frequency doubling.

Description

Technical Field

[0001] The invention relates to the technical field of high-repetition-rate and high-brightness green lasers, and in particular to a high-brightness green laser system using an SBS phase conjugate mirror with a cooling device. Background Art

[0002] In recent years, high-repetition-rate, high-power, short-pulse-width solid-state green lasers have been widely used in many fields, including laser detection, laser radar, laser medical treatment, laser processing, etc. The above-mentioned application fields require sub-nanosecond pulse width and high-energy lasers. The ways to obtain sub-nanosecond lasers include micro-cavity Q-switched sub-nanosecond pulse lasers, mode-locked sub-nanosecond pulse lasers, and sub-nanosecond pulse lasers based on stimulated Brillouin pulse compression. Microchip lasers have low output power due to the small thickness of the laser gain medium. Generally, the output power is increased by increasing the doping concentration of the gain medium, but the potential for increasing the doping concentration is very limited. At present, the output laser is basically in the milliwatt level. Although mode-locked lasers can also obtain narrow pulse width, high-power ultra-short pulse lasers, the lasers obtained by mode-locking technology are not single longitudinal mode pulses, and the output energy is very small. Stimulated Brillouin scattering (SBS) phase conjugation mirror (PCM) is one of the effective methods to generate short pulses and high beam quality lasers. It has the advantages of simple structure, low cost and good output beam quality, and has attracted widespread attention in recent years. Based on the steady-state SBS-PCM technology, long laser pulses can be easily compressed to the sub-nanosecond range while maintaining high energy conversion efficiency. In order to obtain lasers with better beam quality, SBS phase conjugation mirrors are widely used in master-oscillator power amplifier (MOPA) laser systems to compensate for the phase distortion of beams generated by high-power lasers.

[0003] Based on the SBS phase conjugate mirror distortion compensation technology, when the seed light passes through the laser medium for the first time, optical distortion occurs. Due to the phase reversal characteristics of SBS-PCM, after passing through the optical element twice, the distorted light can be restored to the original state of the diffraction limit. At the same time, regardless of the change of the placement of the SBS generating pool, the reflected light path of SBS-PCM is strictly consistent with the incident light path. These significant characteristics are conducive to achieving high-stability and high-quality amplified output. The process of stimulated Brillouin scattering (SBS), that is, the pump pulse is incident on the nonlinear medium, causing the medium to produce an electrostrictive effect, exciting the phonon field, and the phonon field and the photon field are mutually coupled to produce a reverse-transmitting Stokes pulse. The reverse Stokes pulse meets the pump pulse, and the energy is converted from the pump pulse to the Stokes pulse. This process occurs in a very short time, and the final output pulse has the characteristics of narrow pulse width and high energy. It can be combined with MOPA amplification technology and extracavity frequency doubling to obtain green lasers with high repetition rate, sub-nanosecond pulses, and high beam quality.

[0004] Under high repetition rate pumping conditions, using a traditional focusing single-cell structure, impurity particles absorb light in the SBS liquid medium, causing thermal defocusing, thermal haloing, and thermal convection, especially near the focus, which may affect the generation of SBS phase conjugate waves. And as the pump light injection time increases, more and more heat accumulates, resulting in more and more severe spot distortion. In addition, these particles will distort the wavefront, causing a sudden drop in the SBS phase conjugate reflectivity. When the impurity particles are removed from the focal length area, the SBS phase conjugate reflection process needs to be re-established, which affects the reflection energy stability and pulse waveform stability, and pulse width compression cannot achieve good results. For high-power and high-repetition rate SBS pulse compression, it is necessary to select a suitable medium and compression structure to suppress thermal effects. For the selection of the medium, the optical absorption and thermal stability inside the medium are mainly considered. However, there are few studies on improving the compression structure. Summary of the invention

[0005] In view of the technical problems in the existing SBS phase conjugate mirror structure that the high repetition rate and high power laser causes the impurity particles to absorb light, causing thermal defocusing, thermal blooming and thermal convection, the present invention proposes a high-brightness green light laser system using an SBS phase conjugate mirror with a cooling device, which improves the thermal effect in SBS-PCM, realizes SBS pulse output with high beam quality, high energy stability and high compression ratio, and then realizes high-brightness green light laser through external cavity frequency doubling.

[0006] In order to achieve the above-mentioned object, the technical solution of the present invention is implemented as follows: a high-brightness green laser system using an SBS phase conjugate mirror with a cooling device, comprising a seed light and isolation module, an SBS phase conjugate mirror module with a cooling device and a frequency doubling module which are arranged in sequence, the centers of the seed light and isolation module and the SBS phase conjugate mirror module with a cooling device are arranged on the same straight line, and the frequency doubling module corresponds to the seed light and isolation module; After the seed light is output from the output end of the seed light and isolation module, it enters the SBS phase conjugate mirror module with a cooling device, and after the peak power density is increased, the reverse-transmitted Stokes seed light is transmitted again to the output end of the seed light and isolation module, and is reflected from the output end of the seed light and isolation module to the frequency doubling module, where it is amplified and split and converted into high-brightness green laser output.

[0007] The seed light and isolation module includes a laser, an optical path collimation module and an optical path protection module which are arranged in sequence. The center points of the laser, the optical path collimation module and the optical path protection module are arranged on the same straight line. The output end of the optical path protection module and the input end of the SBS phase conjugate mirror module with a cooling device are arranged on the same straight line. The output end of the optical path protection module corresponds to the input end of the frequency doubling module.

[0008] The optical path collimation module comprises a first positive lens and a second positive lens, and the center points of the laser, the first positive lens, the second positive lens and the optical path protection module are all arranged on the same straight line.

[0009] The optical path protection module includes a first polarization beam splitter prism, a Faraday rotator, a half-wave plate and a second polarization beam splitter prism which are arranged in sequence. The center points of the first polarization beam splitter prism and the second positive lens are arranged on the same straight line. The center points of the second polarization beam splitter prism and the SBS phase conjugate mirror module with a cooling device are arranged on the same straight line. The second polarization beam splitter prism corresponds to the input end of the frequency doubling module.

[0010] The SBS phase conjugate mirror module with a cooling device comprises an LD side-pumped amplifier, a quarter-wave plate, a third positive lens and a Brillouin generating cell which are arranged in sequence, and the center points of the LD side-pumped amplifier and the second polarization beam splitter prism are arranged on the same straight line.

[0011] A water cooling module is arranged outside the Brillouin generating pool, the transverse center axis of the Brillouin generating pool and the transverse center axis of the water cooling module are arranged on the same straight line, the upper plane of the Brillouin generating pool and the upper plane of the water cooling module are arranged on the same plane, and the lower plane of the Brillouin generating pool and the lower plane of the water cooling module are arranged on the same plane. The side surfaces of the water cooling module are respectively provided with a first water inlet, a second water inlet, a first water outlet and a second water outlet, and the first water inlet, the second water inlet, the first water outlet and the second water outlet are all connected to the filter.

[0012] The Brillouin generating pool is a cylindrical Brillouin generating pool, the water cooling module is a cylindrical water cooling module, the center of the cylindrical water cooling module and the cylindrical Brillouin generating pool are arranged on the same straight line, the first water inlet and the first water outlet are arranged on both sides of a diameter of the circular cross-section of the cylindrical water cooling module, and the second water inlet and the second water outlet are arranged on both sides of a diameter of the circular cross-section of the cylindrical water cooling module.

[0013] The upper plane and the lower plane of the cylindrical water cooling module are both made of quartz glass, a Brillouin active medium is arranged in the cylindrical Brillouin generating pool, and water is arranged in the cylindrical water cooling module.

[0014] The frequency doubling module comprises a second half wave plate, a fourth positive lens, a KTP crystal and a dichroic mirror which are arranged in sequence. The second half wave plate is matched with the second polarization beam splitter prism through a reflecting mirror.

[0015] The angle between the dichroic mirror and the horizontal plane is 45°.

[0016] The beneficial effects of the present invention are: 1. The present invention proposes a Brillouin generating pool structure with external water cooling, which further improves the thermal effect in SBS and makes the thermal gradient distribution of the inner Brillouin active medium more uniform.

[0017] 2. Compared with the traditional generation pool, it can realize the cooling and temperature control of the generation pool, improve the thermal effect of SBS-PCM, and compensate for the influence of thermal distortion and thermal defocusing on the beam quality.

[0018] 3. Improve the laser beam quality and enhance the frequency doubling conversion efficiency, so that the laser system can achieve hundreds of hertz, sub-nanosecond, high beam quality green laser output. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a structural schematic diagram of the present invention.

[0021] Figure 2 The invention has an external water-cooled Brillouin generating cell structure.

[0022] In the figure, 1 is a seed light and isolation module, 1-1 is a laser, 1-2 is a first positive lens, 1-3 is a second positive lens, 1-4 is a first polarization beam splitter prism, 1-5 is a Faraday rotator, 1-6 is a first half-wave plate, 1-7 is a second polarization beam splitter prism, 2 is an SBS phase conjugate mirror module with a cooling device, 2-1 is an LD side-pumped amplifier, 2-2 is a quarter-wave plate, 2-3 is a third positive lens, 2-4 is a Brillouin generating cell, 3 is a frequency doubling module, 3-1 is a reflector, 3-2 is a second half-wave plate, 3-3 is a fourth positive lens, 3-4 is a KTP crystal, 3-5 is a dichroic mirror, 4-1 is a first water inlet, 4-2 is a second water inlet, 4-3 is a first water outlet, and 4-4 is a second water outlet. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] like Figure 1 As shown, a high-brightness green laser system using an SBS phase conjugate mirror with a cooling device includes a seed light and isolation module 1, an SBS phase conjugate mirror module 2 with a cooling device, and a frequency doubling module 3. The centers of the seed light and isolation module 1 and the SBS phase conjugate mirror module 2 with a cooling device are arranged on the same straight line, and the frequency doubling module 3 corresponds to the seed light and isolation module 1. Among them, the seed light and isolation module 1 is mainly used to generate and adjust the seed light, while preventing the return light from damaging the seed light and isolation module 1. The SBS phase conjugate mirror module 2 with a cooling device is mainly used to convert the seed light into Stokes seed light. The frequency doubling module 3 is mainly used to improve the frequency doubling efficiency of the Stokes seed light and output a high-brightness green laser.

[0025] Specifically, after the seed light is output from the output end of the seed light and isolation module 1, it enters the SBS phase conjugate mirror module 2 with a cooling device, and after the peak power density is increased, the reversely transmitted Stokes seed light is generated and transmitted to the output end of the seed light and isolation module 1 again, and is reflected from the output end of the seed light and isolation module 1 to the frequency doubling module 3, and is amplified and split by the frequency doubling module 3 and converted into a high-brightness green laser output.

[0026] The seed light and isolation module 1 includes a laser 1-1, an optical path collimation module and an optical path protection module which are arranged in sequence. The center points of the laser 1-1, the optical path collimation module and the optical path protection module are arranged on the same straight line. The output end of the optical path protection module and the input end of the SBS phase conjugate mirror module 2 with a cooling device are arranged on the same straight line. The output end of the optical path protection module corresponds to the input end of the frequency doubling module 3. Among them, the laser 1-1 is a single longitudinal mode laser, and the single longitudinal mode laser is mainly used to generate a single longitudinal mode P-type linear polarized pump light. The optical path collimation module includes a first positive lens 1-2 and a second positive lens 1-3. The center points of the laser 1-1, the first positive lens 1-2, the second positive lens 1-3 and the optical path protection module are all arranged on the same straight line. The first positive lens 1-2 and the second positive lens 1-3 are used to collimate the optical path, reduce the divergence angle of the light beam, and achieve long-distance transmission. The optical path protection module includes a first polarization beam splitter prism 1-4, a Faraday rotator 1-5, a half wave plate 1-6 and a second polarization beam splitter prism 1-7 which are arranged in sequence. The center points of the first polarization beam splitter prism 1-4 and the second positive lens 1-3 are arranged on the same straight line. The center points of the second polarization beam splitter prism 1-7 and the SBS phase conjugate mirror module 2 with a cooling device are arranged on the same straight line. The second polarization beam splitter prism 1-7 corresponds to the input end of the frequency doubling module 3. The optical path protection module mainly functions to ensure that the light beam in the optical path can only be transmitted in one direction, and to prevent the return light generated in the optical path from damaging the pump source 1-1. Among them, the first polarization beam splitter prism 1-4 and the second polarization beam splitter prism 1-7 have the function of transmitting P polarized light and reflecting S polarized light. The half wave plate 1-6 and the Faraday rotator 1-5 are used to rotate the optical axis direction of the reversely transmitted Stokes seed light, so that the reversely transmitted Stokes seed light is converted from P polarization to S polarization, and the reversely transmitted Stokes seed light is reflected and output through the first polarization beam splitter prism to prevent the return light generated in the optical path from damaging the single longitudinal mode laser 1-1.

[0027] The SBS phase conjugate mirror module 2 with a cooling device includes an LD side-pumped amplifier 2-1, a quarter-wave plate 2-2, a third positive lens 2-3 and a Brillouin generating pool 2-4, which are arranged in sequence. The center points of the LD side-pumped amplifier 2-1 and the second polarization beam splitter prism 1-7 are arranged on the same straight line. Among them, the LD side-pumped amplifier 2-1 is mainly used to amplify the seed light; the quarter-wave plate 2-2 is mainly used to convert the P polarized light into circularly polarized light; the third positive lens 2-3 is mainly used to increase the peak power density of the circularly polarized light; and the Brillouin generating pool 2-4 is mainly used to generate reversely transmitted Stokes seed light.

[0028] Specifically, after the seed light enters the SBS phase conjugate mirror module 2 with a cooling device, it is first amplified by the LD side pump amplifier 2-1, and then the seed light originally P-polarized light is converted into circularly polarized light by the quarter wave plate 2-2. Then, the circularly polarized light enters the third positive lens 2-3 to increase the peak power density and then enters the Brillouin generating pool 2-4, where the reversely transmitted Stokes seed light is generated. The reversely transmitted Stokes seed light passes through the third positive lens 2-3, and is converted from circularly polarized light to S-polarized light at the quarter wave plate 2-2, and then passes through the LD side pump amplifier 2-1 again. The SBS-PCM phase inversion characteristics are used to compensate for the wavefront distortion of the amplified light beam caused by the thermal lens and thermal spherical aberration effect after high-power amplification. The SBS phase conjugation double-pass amplification and wavefront inversion characteristics are used to automatically compensate for the thermally induced wavefront distortion of the laser amplifier in real time, and obtain a near-diffraction-limited beam output. The reversely transmitted Stokes seed light is refracted by the second polarization beam splitter prism 1-7 and enters the frequency doubling module 3.

[0029] like Figure 2 As shown, the Brillouin generating pool 2-4 includes a cylindrical Brillouin generating pool, a cylindrical water cooling module is arranged outside the cylindrical Brillouin generating pool, the center of the cylindrical water cooling module and the cylindrical Brillouin generating pool are arranged on the same straight line, and the circular surfaces on both sides of the cylindrical water cooling module coincide with the circular surfaces on both sides of the cylindrical Brillouin generating pool, that is, the two side surfaces of the cylindrical water cooling module coincide with the two side surfaces of the cylindrical Brillouin generating pool. The cylindrical water cooling module and the circular surfaces of the cylindrical Brillouin generating pool are both made of quartz glass, a Brillouin active medium is arranged in the cylindrical Brillouin generating pool, and water is arranged in the cylindrical water cooling module.

[0030] The first water inlet 4-1, the second water inlet 4-2, the first water outlet 4-3 and the second water outlet 4-4 are respectively arranged on the side of the cylindrical water cooling module, and the first water inlet 4-1, the second water inlet 4-2, the first water outlet 4-3 and the second water outlet 4-4 are all connected to the filter. The first water inlet 4-1 and the first water outlet 4-3 are arranged on both sides of a diameter of the circular cross section of the cylindrical water cooling module, and the second water inlet 4-2 and the second water outlet 4-4 are arranged on both sides of a diameter of the circular cross section of the cylindrical water cooling module.

[0031] By setting a cylindrical water cooling module outside the cylindrical Brillouin generating pool, the Brillouin generating pool 2-4 can be evenly cooled, and the thermal effect in the SBS can be further improved, so that the thermal gradient distribution of the inner Brillouin active medium is more uniform, thereby outputting high repetition rate, high beam quality sub-nanosecond laser. At the same time, in order to avoid excessive water pressure causing vibration of the inner Brillouin active medium and affecting the refractive index of the medium, the diameter of the water inlet and outlet should not be too small, and a quick-insert threaded connector with an inner diameter of 12 mm is selected.

[0032] The frequency doubling module 3 includes a second half wave plate 3-2, a fourth positive lens 3-3, a KTP crystal 3-4 and a dichroic mirror 3-5 arranged in sequence. The second half wave plate 3-2 is matched with the second polarization beam splitter prism 1-7 through a reflector 3-1. Among them, the reflector 3-1 is mainly used to reflect the reversely transmitted Stokes seed light and input it into the second half wave plate 3-2. The second half wave plate 3-2 is mainly used to adjust the polarization state of the reversely transmitted Stokes seed light. In order to meet the crystal birefringence phase matching, the second half wave plate is rotated so that the polarization state of the Stokes light meets the phase matching condition to achieve the maximum frequency doubling efficiency. The fourth positive lens 3-3 is mainly used to improve the peak power density and improve the frequency doubling efficiency. The KTP crystal 3-4 is mainly used to double the 1064nm laser to a 532nm laser. The dichroic mirror 3-5 is mainly used to reflect 1064nm laser and output 532nm high-brightness green laser. The angle between the dichroic mirror 3-5 and the horizontal plane is 45°.

[0033] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high brightness green laser system using an SBS phase conjugate mirror with a cooling device, characterized in that: It comprises a seed light and isolation module (1), an SBS phase conjugate mirror module (2) with a cooling device, and a frequency doubling module (3) which are arranged in sequence, wherein the centers of the seed light and isolation module (1) and the SBS phase conjugate mirror module (2) with a cooling device are arranged on the same straight line, and the frequency doubling module (3) corresponds to the seed light and isolation module (1); After the seed light is output from the output end of the seed light and isolation module (1), it enters the SBS phase conjugate mirror module (2) with a cooling device, and after the peak power density is increased, the reversely transmitted Stokes seed light is generated and transmitted again to the output end of the seed light and isolation module (1), and is reflected from the output end of the seed light and isolation module (1) to the frequency doubling module (3), and is amplified and split by the frequency doubling module (3) and converted into a high-brightness green laser output.

2. The high brightness green laser system using the SBS phase conjugate mirror with a cooling device according to claim 1, characterized in that: The seed light and isolation module (1) comprises a laser (1-1), an optical path collimation module and an optical path protection module which are arranged in sequence, wherein the center points of the laser (1-1), the optical path collimation module and the optical path protection module are arranged on the same straight line, the output end of the optical path protection module and the input end of an SBS phase conjugate mirror module (2) with a cooling device are arranged on the same straight line, and the output end of the optical path protection module corresponds to the input end of the frequency doubling module (3).

3. The high brightness green laser system using the SBS phase conjugate mirror with a cooling device according to claim 2, characterized in that: The optical path collimation module comprises a first positive lens (1-2) and a second positive lens (1-3), and the center points of the laser (1-1), the first positive lens (1-2), the second positive lens (1-3) and the optical path protection module are all arranged on the same straight line.

4. The high brightness green laser system using the SBS phase conjugate mirror with a cooling device according to claim 3, characterized in that: The optical path protection module comprises a first polarization beam splitter prism (1-4), a Faraday rotator (1-5), a half-wave plate (1-6) and a second polarization beam splitter prism (1-7) which are arranged in sequence; the center points of the first polarization beam splitter prism (1-4) and the second positive lens (1-3) are arranged on the same straight line; the center points of the second polarization beam splitter prism (1-7) and an SBS phase conjugate mirror module (2) with a cooling device are arranged on the same straight line; and the second polarization beam splitter prism (1-7) corresponds to an input end of the frequency doubling module (3).

5. The high brightness green laser system using the SBS phase conjugate mirror with a cooling device according to any one of claims 2 to 4, characterized in that: The SBS phase conjugate mirror module (2) with a cooling device comprises an LD side-pumped amplifier (2-1), a quarter-wave plate (2-2), a third positive lens (2-3) and a Brillouin generating pool (2-4) which are arranged in sequence, and the center points of the LD side-pumped amplifier (2-1) and the second polarization beam splitter prism (1-7) are arranged on the same straight line.

6. The high brightness green laser system using the SBS phase conjugate mirror with a cooling device according to claim 5, characterized in that: A water cooling module is arranged outside the Brillouin generating pool (2-4); a transverse central axis of the Brillouin generating pool (2-4) and a transverse central axis of the water cooling module are arranged on the same straight line; an upper plane of the Brillouin generating pool (2-4) and an upper plane of the water cooling module are arranged on the same plane; a lower plane of the Brillouin generating pool (2-4) and a lower plane of the water cooling module are arranged on the same plane; a first water inlet (4-1), a second water inlet (4-2), a first water outlet (4-3) and a second water outlet (4-4) are respectively arranged on the side of the water cooling module; and the first water inlet (4-1), the second water inlet (4-2), the first water outlet (4-3) and the second water outlet (4-4) are all connected to the filter.

7. The high brightness green laser system using the SBS phase conjugate mirror with a cooling device according to claim 6, characterized in that: The Brillouin generating pool (2-4) is a cylindrical Brillouin generating pool, the water cooling module is a cylindrical water cooling module, the centers of the cylindrical water cooling module and the cylindrical Brillouin generating pool are arranged on the same straight line, the first water inlet (4-1) and the first water outlet (4-3) are arranged on both sides of a diameter of a circular cross section of the cylindrical water cooling module, and the second water inlet (4-2) and the second water outlet (4-4) are arranged on both sides of a diameter of a circular cross section of the cylindrical water cooling module.

8. The high brightness green laser system using the SBS phase conjugate mirror with a cooling device according to claim 7, characterized in that: The upper plane and the lower plane of the cylindrical water cooling module are both made of quartz glass, a Brillouin active medium is arranged in the cylindrical Brillouin generating pool, and water is arranged in the cylindrical water cooling module.

9. The high brightness green laser system using the SBS phase conjugate mirror with a cooling device according to claim 7 or 8, characterized in that: The frequency doubling module (3) comprises a second half-wave plate (3-2), a fourth positive lens (3-3), a KTP crystal (3-4) and a dichroic mirror (3-5) which are arranged in sequence; the second half-wave plate (3-2) is matched with a second polarization beam splitting prism (1-7) via a reflector (3-1).

10. The high brightness green laser system using the SBS phase conjugate mirror with a cooling device according to claim 9, characterized in that: The angle between the dichroic mirror (3-5) and the horizontal plane is 45°.

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