Single longitudinal mode laser based on LED pumping

Abstract

A single longitudinal mode laser based on LED pumping comprises a plane mirror, two sets of LED pumping modules and an output mirror which are sequentially connected in series, an optical rotation crystal is connected between the two sets of LED pumping modules in series, and an LED array serves as a pumping source to provide excitation energy in the laser and excite electrons in a gain medium to transition from a low energy state to a high energy state, so that stimulated radiation is generated. When light emitted by the LED irradiates the gain medium, the medium absorbs light energy and enters an excited state, and then laser output is achieved in the resonant cavity through stimulated emission. The ring cavity single longitudinal mode technology combines the advantages of high flexibility, high stability and easy regulation and control, the performance and the application range of the single longitudinal mode laser are greatly enhanced, and the ring cavity single longitudinal mode technology is particularly prominent in the fields of precision optical application and nonlinear optics. The method overcomes the limitation of a traditional single longitudinal mode laser in the aspects of single longitudinal mode stability, mode competition and output stability, and shows powerful technical potential.

Description

Technical Field

[0001] The invention relates to the technical field of laser and optoelectronics, and in particular to a single longitudinal mode laser based on LED pumping. Background Art

[0002] Compared with multi-mode lasers, single longitudinal mode lasers not only have the advantages of strong stability and good beam quality, but also have narrow output spectrum and good coherence. They play an important role in sodium guide star technology, Doppler wind radar, optical communication, precision ranging, gravitational wave detection, nonlinear optics, industry and national defense. Among them, solid-state single longitudinal mode lasers have the advantages of wide operating wavelength range and strong power scalability, and have received widespread attention and application. However, for solid-state lasers, to achieve stable single longitudinal mode operation, different longitudinal mode selection technologies need to be adopted according to different working conditions.

[0003] 1. Short cavity method It means that no longitudinal mode selection device is used in the cavity, and the longitudinal mode interval Δνq can be increased by simply reducing the cavity length L, so that only one longitudinal mode with a gain greater than the threshold exists in the gain spectrum line width to achieve single longitudinal mode output.

[0004] For example, the LD end-pumped highly doped Er:GGG microchip laser with a thickness of 600 μm obtained a laser output with a central wavelength of 1.048 μm, a maximum output power of 50.8 mW, and a maximum single pulse energy of 0.306 mJ.

[0005] 2. Inner cavity etalon method The intracavity etalon method utilizes the principle of multi-beam interference. When the etalon is inserted, only the longitudinal mode with the highest transmittance oscillates in the cavity, while other modes cannot reach the threshold due to low transmittance and thus cannot oscillate. The etalon increases the net gain difference between different longitudinal modes to achieve single longitudinal mode output.

[0006] For example, by using a 443nm blue light LD to pump a Pr: YLF crystal and adopting the intracavity double standard tool method, a single longitudinal mode output power of 9 mW and a spectral width of 18 MHz single longitudinal mode green light output was achieved.

[0007] 3. Twisting Cavity Method The structure of the twisted cavity method is to place two λ / 4 wave plates with perpendicular fast axes at both ends of the gain medium crystal, so that circularly polarized light passes through the inside of the gain medium, the light field evenly consumes the inverted number of particles, and the spatial hole burning effect is eliminated to select the longitudinal mode.

[0008] For example, the LD-pumped Pr:YLF twisted-mode cavity laser, under the action of 3.5 W blue light pumping, obtained a 640 nm single longitudinal mode laser output with a slope efficiency of 26.8%, an output power of 403 mW, and a linewidth of 150 MHz.

[0009] 4. Parallel annular cavity A planar ring cavity, also known as a discrete element ring cavity, is composed of three or more cavity mirrors. By inserting an optical isolator into the cavity, the unidirectional traveling wave operation of the laser is realized, the spatial hole burning effect is eliminated, and a single longitudinal mode laser output is obtained.

[0010] For example, an imaging system was used in a double-end pumped "8"-type ring cavity in combination with an LBO frequency-doubling crystal to obtain a 101 W high-power continuous single-longitudinal mode laser output.

[0011] The above existing longitudinal mode selection technology has the following technical problems: The output power is low, and it is difficult to add other devices in the cavity to improve the output characteristics; the processing accuracy requirements are high; the mode selection ability is poor; under high-power operation, thermal effects will reduce the beam quality and stability; precision components and special materials make the manufacturing and maintenance costs high.

[0012] Mode competition: Mode competition of different wavelengths in the cavity can easily cause unstable output of a single longitudinal mode.

[0013] Poor cavity length controllability: In existing designs, the spacing and adjustable range of optical elements are limited by the cavity length.

[0014] Influence of thermal effects: Under LD high-density pumping conditions, the thermal effects and thermally induced birefringence effects inside the laser crystal will significantly reduce the beam quality, power stability and single longitudinal mode output stability.

[0015] High cost: High-performance pump source LD, precision wavelength tuning components and special laser cavity mirror film systems make the design, manufacturing and maintenance costs high. Summary of the invention

[0016] The present invention provides a single longitudinal mode laser based on LED pumping. The LED module side pump technology has the advantages of high beam quality, low thermal lens effect, etc., has the benefit of greatly increasing the cavity length without attenuating the power, and can also greatly improve the beam quality. The ring cavity single longitudinal mode technology combines the advantages of high flexibility, high stability and easy control, greatly enhancing the performance and application range of single longitudinal mode lasers, especially in the fields of precision optical applications and nonlinear optics. This method overcomes the limitations of traditional single longitudinal mode lasers in single longitudinal mode stability, mode competition and output stability, and shows strong technical potential.

[0017] A single longitudinal mode laser based on LED pumping comprises a plane mirror, two groups of LED pumping modules and an output mirror connected in series in sequence, an optical rotation crystal is connected in series between the two groups of LED pumping modules, the laser generated by the LED pumping module close to the plane mirror is reflected to the output mirror through the plane mirror, passes through the output mirror and then passes through a polarizer to reach a second plano-concave mirror, the laser reflected by the second plano-concave mirror passes through a 1 / 2 wave plate and a Faraday rotator and then passes through a first plano-concave mirror, is reflected to the plane mirror through the first plano-concave mirror, is reflected to the output mirror through the plane mirror, and is output through the output mirror.

[0018] Furthermore, the surface of the plane mirror of the present invention is coated with a film system that is highly reflective to 1064nm light, which completely reflects the light beam and ensures that the photons in the resonant cavity are reflected and circulated in a ring path.

[0019] Furthermore, the specific structure of the LED pump module of the present invention is as follows: it includes a laser rod located at a central position, a glass sleeve is arranged on the periphery of the laser rod in the length direction, a support frame is arranged on the periphery of the glass sleeve, a plurality of groups of water-cooled copper blocks are evenly arranged on the support frame, an LED stacking array is arranged on one side of each group of water-cooled copper blocks close to the glass sleeve, each LED stacking array includes an LED light bar and a PCB board for fixing the LED light bar, and the PCB board is connected to the water-cooled copper block; Cooling water circulation modules are respectively arranged at both ends of the laser rod in the length direction, and water holes are respectively arranged on the cooling water circulation module and the water-cooled copper block.

[0020] Furthermore, each LED light strip of the present invention includes 20 LED lamp beads forming a row of LED stacked arrays, and the LED lamp beads are SMD LEDs with an emission center wavelength of 810nm, a half-peak width of 30nm, and a beam angle of 90°.

[0021] Furthermore, the LED of the present invention is a continuous pump output.

[0022] Furthermore, the gain medium of the LED pump module of the present invention is a neodymium-doped cerium-doped yttrium aluminum garnet crystal; both ends are sealed in a cooling water circulation module.

[0023] Furthermore, the optically active crystal of the present invention is used to compensate for the change in the polarization state of the light beam caused by birefringence or stress due to thermal effects in the gain medium, thereby improving the output stability of the laser.

[0024] Furthermore, the Faraday rotator of the present invention is a ferromagnetic crystal surrounded by a strong permanent magnet to form a magneto-optical device; linearly polarized light sent through the Faraday rotator will be rotated by 45° regardless of the input angle.

[0025] Furthermore, the surface of the plano-concave mirror of the present invention is coated with a film system that is highly reflective to 1064nm light, and has a radius of curvature of 300mm, which converges the light beam in the cavity and controls the cross-sectional size of the light beam.

[0026] Furthermore, the surface of the output mirror of the present invention is coated with a film system of T=5%@1064nm, which outputs laser light and optimizes the energy balance in the resonant cavity.

[0027] The present invention adopts the above technical solution and has the following advantages compared with the prior art: 1. The main function of the LED array used as the pump source in the laser is to provide excitation energy to stimulate the electrons in the gain medium, neodymium-doped cerium-doped yttrium aluminum garnet (Nd, Ce: YAG), to transition from a low energy state to a high energy state, thereby generating stimulated radiation. When the light emitted by the LED irradiates the gain medium, the medium absorbs the light energy and enters an excited state, and then realizes laser output through stimulated emission in the resonant cavity. The LED module side pump technology has the advantages of high beam quality and low thermal lens effect, and has the benefit of greatly increasing the cavity length without attenuating the power, and can also greatly improve the beam quality.

[0028] 2. The ring resonator of the present invention adopts a ring optical path structure, and cooperates with non-reciprocal elements such as Faraday rotators to ensure that the light beam propagates in a single direction (clockwise or counterclockwise) in the cavity. The unidirectional propagation avoids the formation of standing waves in traditional linear resonators, effectively eliminates the spatial hole burning effect, and thus suppresses multi-mode oscillation. The reverse light beam is absorbed by the optical isolator or deflected out of the ring path to prevent feedback interference.

[0029] 3. The ring resonator of the present invention adopts a ring optical path structure, which realizes the adjustment of output power in the resonator, and at the same time has low requirements on processing accuracy. Even under high power operation, the beam quality and stability can be guaranteed.

[0030] 4. The present invention has a simple structure and low manufacturing and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the laser resonant cavity system of the present invention.

[0032] Figure 2 It is a cross-sectional schematic diagram of the LED pump module of the present invention.

[0033] Figure 3 It is a schematic longitudinal section diagram of the LED pump module of the present invention. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is described in detail below with reference to the accompanying drawings: like Figure 1As shown, a single longitudinal mode laser based on LED pumping comprises a plane mirror 1, two groups of LED pumping modules, and an output mirror 5 connected in series in sequence, an optical rotation crystal 3 is connected in series between the two groups of LED pumping modules, the laser generated by the LED pumping module close to the plane mirror 1 is reflected to the output mirror 5 through the plane mirror 1, and then reaches the second plano-concave mirror 16 after passing through the output mirror 5 and the polarizer 6, and the laser reflected by the second plano-concave mirror 16 passes through the 1 / 2 wave plate 17 and the Faraday rotator 18 and then passes through the first plano-concave mirror 15, and then reflects to the plane mirror 1 through the first plano-concave mirror 15, and then reflects to the output mirror 5 through the plane mirror 1, and then outputs through the output mirror 5. The red line in the figure represents the propagation path of the laser.

[0035] The detailed laser transmission path is shown below: 1. Pump light injection 1. LED array pump source: Figure 1 Two LED pump modules are shown in Figure 1, each with five LED arrays surrounding the gain medium (Nd, Ce:YAG). The pump light provided by the LED array is incident on the gain medium at the appropriate wavelength to excite the rare earth ions in the Nd, Ce:YAG crystal, causing them to transition to higher energy levels.

[0036] 2. Gain medium (Nd, Ce:YAG): After pumping, the rare earth ions in the gain medium are excited from the ground state to the high energy state. Subsequently, these ions return to the low energy state through stimulated radiation, releasing laser photons.

[0037] 2. Generation of initial light 1. Stimulated radiation: When the stimulated radiation photons in the gain medium reach a certain threshold, these photons are further amplified through the round-trip propagation between the reflective lenses of the resonant cavity, forming laser oscillations.

[0038] 2. Resonant cavity function: Output mirror 5 is an output coupling mirror, which partially transmits the laser light. Plane mirror 1, first plano-concave mirror 15 and second plano-concave mirror 16 are high reflective mirrors, which are used to reflect the laser light back to the gain medium.

[0039] 3. Initial light formation: Photons interact with the gain medium during the process of reflecting back and forth in the resonant cavity, causing the number of photons to increase rapidly.

[0040] 3. Laser Propagation Path 1. Initial propagation: After the laser is generated from the gain medium, it propagates along the two-way resonant cavity. The forward traveling wave is reflected by plane mirror 1 to output mirror 5, reflected by output mirror 5 to the second plano-concave mirror 16, reflected by the second plano-concave mirror 16 to the first plano-concave mirror 15, reflected by the first plano-concave mirror 15 to plane mirror 1, reflected by plane mirror 1 to output mirror 5, and output through output mirror 5. The reverse traveling wave is reflected by plane mirror 1 to the first plano-concave mirror 15, and the laser reflected by the first plano-concave mirror 15 reaches the second plano-concave mirror 16. The laser reflected by the second plano-concave mirror 16 is output through output mirror 5.

[0041] 2. Beam polarization control: Faraday rotator (FR) and half-wave plate (HWP): used to adjust the laser polarization state to ensure the operation of single polarization mode in the cavity. Brewster plate: further selectively enhances photons with a specific polarization direction. These three optical elements form an optical isolator in the cavity to achieve unidirectional traveling wave operation of the laser, eliminate the spatial hole burning effect, and obtain single longitudinal mode laser output.

[0042] 4. Laser output: The laser light is partially transmitted through the output mirror 5 and finally output as the laser light.

[0043] In summary, the surface of the plane mirror 1 of the present invention is coated with a film system that is highly reflective to 1064nm light, which completely reflects the light beam and ensures that the photons in the resonant cavity are reflected and circulated in a ring path.

[0044] like Figure 2 , 3 As shown, the specific structure of the LED pump module of the present invention is as follows: it includes a laser rod 7 located at the center, a glass sleeve 8 is arranged on the periphery of the laser rod 7 in the length direction, a support frame 9 is arranged on the periphery of the glass sleeve 8, a plurality of groups of water-cooled copper blocks 10 are evenly arranged on the support frame 9, an LED stacking array is arranged on one side of each group of water-cooled copper blocks 10 close to the glass sleeve, each LED stacking array includes an LED light bar 11 and a PCB board 12 for fixing the LED light bar, and the PCB board is connected to the water-cooled copper block; Cooling water circulation modules 13 are respectively arranged at both ends of the laser rod in the length direction, and water holes 14 are respectively arranged on the cooling water circulation module 13 and the water-cooled copper block 10 .

[0045] The optically active crystal 3 of the present invention is used to compensate for the change in the polarization state of the light beam caused by the double refraction or stress due to the thermal effect in the gain medium, thereby improving the output stability of the laser.

[0046] The surface of the output mirror 5 of the present invention is coated with a film system of T=5%@1064nm, outputs laser light, and optimizes the energy balance in the resonant cavity.

[0047] The polarizer 6 of the present invention is used to convert the light of different polarities emitted by the gain medium into linearly polarized light.

[0048] The surfaces of the first plano-concave mirror 15 and the second plano-concave mirror 16 of the present invention are coated with a film system that is highly reflective to 1064nm light, and the radius of curvature is 300mm, which converges the light beam in the cavity and controls the cross-sectional size of the light beam.

[0049] The half wave plate 17 of the present invention is used to adjust the polarization direction of the incident light to optimize the matching with the Faraday rotator.

[0050] The Faraday rotator 18 of the present invention is a ferromagnetic crystal surrounded by strong permanent magnets to form a magneto-optical device; linearly polarized light sent through the Faraday rotator will be rotated 45° regardless of the input angle.

[0051] The "LED array" of the present invention is a pump light source for lasers. The LED array provides pump light, injects energy into the gain medium through the semiconductor light emitting diode array, and thus stimulates the generation of lasers. Each LED light bar of the present invention includes 20 LED lamp beads to form a row of LED stacked arrays. The LED lamp beads are SMD LEDs with an emission center wavelength of 810nm, a half-peak width of about 30nm, and a beam angle of 90°. The LED is a continuous pump output.

[0052] The gain medium of the LED pump module of the present invention is a neodymium-doped cerium-doped yttrium aluminum garnet (Nd, Ce: YAG) crystal; both ends are sealed in a cooling water circulation module. As a laser medium, after the addition of cerium ions (Ce³⁺), light amplification and laser output can be achieved. It is suitable for higher power output and often works in the near-infrared band.

[0053] The structural features of the present invention are specifically: 1. Using LED side pumping device can significantly improve the LED pump light coupling efficiency, improve the laser beam quality, increase the working life of the laser system and significantly reduce the cost of the laser system. 1. Changed the pump source LED has a moderately broad emission spectrum, which is conducive to better overlap between the average output power of the fundamental laser and a group of high absorption lines in the laser medium, so an efficient LED is used as a pump source to pump the gain medium.

[0054] 2. Designed a new pump module The pump module is newly designed with a pentagonal LED array surrounding the laser rod (such as Figure 2 , Figure 3 As shown in Figure 3, sufficient pump power density was obtained.

[0055] 3. Improve pump light coupling efficiency: The LED side pumping configuration enables the pump light to propagate better in the gain medium. Through side pumping, the pump light can interact with the gain medium over a longer path, improving the light absorption efficiency. This configuration allows the pump light to be more evenly distributed in the gain medium compared to other pumping methods (such as end pumping), thereby improving the coupling efficiency of the pump light.

[0056] 4. Reduce spot distortion: Since the divergence angle of the LED pump light source is large and the incident angle with the gain medium is usually small, the LED side pumping light beam can be evenly distributed on the surface of the gain medium, reducing beam distortion and concentration effects, and helping to improve the beam quality of the laser output.

[0057] 5. Reduce the internal thermal effect of the laser crystal: Since the light source of LED side pumping is widely distributed, it can usually work at a higher power without causing local overheating like end pumping. The lower heat density and uniform pumping method of LED make the thermal management of the overall system more efficient under high-power pumping, significantly reduce the internal thermal effect of the laser crystal, and maintain a longer working life.

[0058] 6. Significantly reduce the cost of the laser system: Under the same output power conditions, the cost of a single LED tube is much lower than that of a single LD tube. At the same time, the supporting system support and protection structure are greatly simplified, and the external power supply adopts a low current and high voltage power supply mode, which significantly reduces the cost of the entire laser system.

[0059] 2. Using a planar ring cavity to significantly improve the stability of single longitudinal mode laser output and reduce system complexity 1. Stable output power: The ring cavity is a traveling wave oscillator, which can effectively eliminate the standing wave effect and spatial hole burning effect in the cavity. A isolator is inserted in the cavity to achieve unidirectional laser output, making the central wavelength and average power of the single longitudinal mode laser output more balanced and stable, and not easily affected by external factors. Compared with the traditional LD ​​pumped dual-wavelength laser, it is easily affected by external factors such as LD temperature drift, cavity vibration, and working environment temperature during operation, resulting in the deviation of the central wavelength of the dual-wavelength laser output and wavelength annihilation, which further affects the stability of the output power.

[0060] 2. Change the curvature of the reflector and the film system of the output mirror The light beam in the resonant cavity can be converged to control the cross-sectional size of the light beam and optimize the spot quality. The design of intracavity components (such as plano-concave mirrors) improves the selectivity of transverse and longitudinal modes and avoids multi-mode oscillation.

[0061] 3. Enhanced one-way propagation gain efficiency The Faraday rotator 18 is used to achieve unidirectional propagation, completely eliminating the spatial hole burning effect and ensuring the high stability of the single longitudinal mode output. The cavity mirror is optimized to significantly improve the frequency selectivity and achieve narrow line width single longitudinal mode output.

[0062] 4. Use optically active crystals to reduce the thermal effect and spatial hole burning effect of laser resonators An optically active crystal 3 is placed between the first LED pump module 2 and the second LED pump module 4 to reduce the spatial hole burning effect. By adding an optically active crystal, the polarization state of light can be rotated, and the propagation characteristics of light in the resonant cavity can be changed, thereby reducing the impact of this effect on the laser output and improving the stability and efficiency of the laser. The optically active crystal can also be used to compensate for the change in the polarization state of the light beam caused by birefringence or stress caused by thermal effects in the gain medium, thereby improving the output stability of the laser.

[0063] Technical Effects of the Invention: 1. High efficiency and high stability a. High light conversion efficiency: By adopting the ring cavity technology, the laser output power can be effectively increased, thereby improving the conversion efficiency of the overall system. Due to the use of curved reflectors, higher energy density can be obtained in the cavity and more effective energy transfer can be performed, reducing energy loss.

[0064] b. Higher stability: Ring cavity technology can make the output wavelength of the laser more stable. Compared with other single longitudinal mode cavity modulation technologies, the ring cavity ensures the single-mode characteristics of the laser output and avoids the instability caused by laser mode competition.

[0065] 2. Improve output beam quality Improve beam quality: LED pumping has low thermal lens effect, which can effectively increase the cavity length, thus providing better beam quality. And by using curved reflectors, the output laser beam can maintain good focusing characteristics, reducing beam distortion caused by non-ideal optical modes.

[0066] 3. Higher flexibility and adjustability Flexible adjustment of cavity length: LED pumps have low thermal lens effect, which can effectively increase the cavity length. Different optical elements can be added in the cavity to obtain different effects, providing more options and customization capabilities.

[0067] 4. Widely used a. Nonlinear frequency conversion: Single longitudinal mode lasers based on ring cavities are very suitable for nonlinear frequency conversion processes, such as optical parametric amplification (OPA), optical parametric oscillation (OPO), etc. These processes require laser sources with different wavelengths to achieve efficient frequency conversion and generate lasers with new wavelengths.

[0068] b. Application of single longitudinal mode laser source: In some specific scientific research and industrial applications, single longitudinal mode lasers can provide specific wavelengths to meet different needs. For example, some biomedical imaging technologies, LiDAR or environmental monitoring require single longitudinal mode lasers for multi-angle data collection.

[0069] 5. Simplify design and integration a. Save space and reduce the number of components: LED pump technology is directly integrated into the laser cavity, without the need for external complex optical adjustment systems or multiple pump light sources. This simplifies system design, reduces the use of external components, and reduces the size and cost of the system.

[0070] b. Improve the reliability of the overall system: The LED pump module adopts a modular design, which reduces the errors and unstable factors introduced by multiple laser sources and optical paths, and improves the reliability of the entire laser system.

Claims

1. A single longitudinal mode laser based on LED pumping, characterized in that The invention comprises a plane mirror, two groups of LED pump modules and an output mirror connected in series in sequence. An optical rotation crystal is connected in series between the two groups of LED pump modules. The laser generated by the LED pump module close to the plane mirror is reflected to the output mirror through the plane mirror, passes through the output mirror and then passes through a polarizer to reach a second plano-concave mirror. The laser reflected by the second plano-concave mirror passes through a 1 / 2 wave plate and a Faraday rotator and then passes through the first plano-concave mirror, is reflected to the plane mirror through the first plano-concave mirror, is reflected to the output mirror through the plane mirror, and is output through the output mirror.

2. The LED-pumped single longitudinal mode laser according to claim 1, characterized in that The surface of the plane mirror is coated with a film system that is highly reflective to 1064nm light, which completely reflects the light beam and ensures that the photons in the resonant cavity are reflected and circulated in a ring path.

3. The LED-pumped single longitudinal mode laser according to claim 1, characterized in that The specific structure of the above LED pump module is as follows: it includes a laser rod located at the center, a glass sleeve is arranged on the periphery of the laser rod in the length direction, a support frame is arranged on the periphery of the glass sleeve, a plurality of groups of water-cooled copper blocks are evenly arranged on the support frame, an LED stacking array is arranged on one side of each group of water-cooled copper blocks close to the glass sleeve, each LED stacking array includes an LED light bar and a PCB board for fixing the LED light bar, and the PCB board is connected to the water-cooled copper block; Cooling water circulation modules are respectively arranged at both ends of the laser rod in the length direction, and water holes are respectively arranged on the cooling water circulation module and the water-cooled copper block.

4. The LED-pumped single longitudinal mode laser according to claim 3, characterized in that Each of the above-mentioned LED light strips includes 20 LED lamp beads to form a row of LED stacked arrays. The LED lamp beads are surface-mount LEDs with an emission center wavelength of 810nm, a half-peak width of 30nm, and a beam angle of 90°.

5. The LED-pumped single longitudinal mode laser according to claim 4, characterized in that The above LEDs are continuous pump outputs.

6. The LED-pumped single longitudinal mode laser according to claim 3, characterized in that The gain medium of the LED pump module is a neodymium-doped cerium-doped yttrium aluminum garnet crystal; both ends are sealed in a cooling water circulation module.

7. The LED-pumped single longitudinal mode laser according to claim 1, characterized in that The optically active crystal is used to compensate for the change in the polarization state of the light beam caused by birefringence or stress due to thermal effects in the gain medium, thereby improving the output stability of the laser.

8. The LED-pumped single longitudinal mode laser according to claim 1, characterized in that The Faraday rotator described above is a ferromagnetic crystal surrounded by strong permanent magnets to form a magneto-optical device; linearly polarized light sent through the Faraday rotator will be rotated 45° regardless of the input angle.

9. The LED-pumped single longitudinal mode laser according to claim 1, characterized in that The surface of the plano-concave mirror is coated with a film system that is highly reflective to 1064nm light, and the radius of curvature is 300mm. It converges the light beam in the cavity and controls the cross-sectional size of the light beam.

10. The LED-pumped single longitudinal mode laser according to claim 1, characterized in that The surface of the output mirror is coated with a film system of T=5%@1064nm, which outputs laser and optimizes the energy balance in the resonant cavity.

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