Laser for realizing high-power pump beam quality enhancement based on multi-stack heat transfer

Abstract

The invention belongs to the field of solid lasers, and particularly relates to a laser for realizing high-power pump beam quality enhancement based on multi-stack heat transfer, which comprises a pump module, a pump shaping coupling module, a multi-stack crystal, a cube-corner prism, an output mirror and a cooling device. And the multi-laminated crystal adopts a high-thermal-conductivity diamond film, so that transverse rapid diffusion of heat is realized, local heat accumulation and temperature rise are relieved, wavefront distortion and a thermal lens effect caused by thermally induced refractive index change are reduced, and the stability of a laser mode is improved. The cube-corner prism is used as a resonant cavity mirror surface, can automatically compensate angle deviation, optimizes mode matching in the cavity, has a synergistic effect with a zigzag total internal reflection path in the crystal, further balances a heat affected zone, improves light field distribution, and remarkably improves light beam uniformity, stability and TEM00 mode quality. The structure is high in adaptability, is suitable for various wavelengths, pumping modes and thermal loads, and assists the laser to realize miniaturized, high-integration and high-performance output.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state lasers, and particularly to a laser for enhancing the quality of high-power pump beams based on multi-layer heat transfer. Background Art

[0002] High-power solid-state lasers have extensive and in-depth applications in industries, medical fields, and military industries such as material processing, laser cleaning, laser surgery, laser guidance, and lidar. Under the condition of high-power end-pumping, the non-uniform longitudinal absorption of the pump light in the laser medium will cause significant thermal effects. Usually, water cooling is used to ensure that the laser medium is not damaged by excessive temperature. However, the severe thermal effects exacerbate the non-axisymmetry of the laser, resulting in a thermal lens effect, which changes the propagation path of the laser beam, causes the resonator to detune, affects the quality of the laser output, and even the thermal stress may directly damage the laser crystal.

[0003] People often use bonded crystals to reduce thermal effects, or use methods such as thermal boosting to effectively suppress thermal relaxation. However, as the power increases, it will inevitably cause high-order mode oscillations of the laser, and the generation of a large number of non-fundamental modes will seriously affect the beam quality. In order to maintain the low-order mode operating state of the laser, it is necessary to effectively limit the high-order modes, but this limitation will inevitably weaken the laser output power, resulting in a relatively low end-pumping output power.

[0004] Therefore, side-pumping is often used to obtain high-power output. The side-pumping structure can provide a larger pump area, reduce the power density of a single pump light source, thereby improving the tolerance of the crystal. However, it is more likely to cause beam mode distortion. Usually, a 4f imaging system or a double-rod series connection structure is used to compensate for the thermal effect, and the resonator is optimized to obtain TEM 00 mode output, but its structure is very complex. Summary of the Invention

[0005] (1) Technical Problems to be Solved

[0006] In view of the deficiencies of the prior art, the present invention provides a laser for enhancing the quality of high-power pump beams based on multi-layer heat transfer, which solves the problems raised in the above background art.

[0007] (2) Technical Solutions

[0008] The present invention adopts the following technical solutions to achieve the above objectives:

[0009] A laser for enhancing the quality of high-power pump beams based on multi-layer heat transfer includes a pump module, a pump shaping and coupling module, a multi-layer crystal, a corner cube prism, an output mirror, and a cooling device;

[0010] The pump module generates pump light to excite the multi-stack crystal, providing stable energy to achieve population inversion of the crystal, and is located directly above the multi-stack crystal.

[0011] The pump shaping and coupling module is located between the light output port of the pump module and the multi-stack crystal, and the pump light is shaped by the pump shaping and coupling module and then enters the multi-stack crystal.

[0012] The multi-stack crystal is stacked by crystal material and diamond film. The laser incident surface of the multi-stack crystal is the crystal material with roughened surface to avoid parasitic oscillation. The inside of the crystal is diamond film. The end faces of the multi-stack crystal are coated with laser antireflection film, and the other faces are coated with diamond film to facilitate rapid heat removal from the crystal. The oscillating laser propagates in a "zigzag" shape through total internal reflection inside the multi-stack crystal, so that the uneven thermal effects in different regions of the laser in the y direction cancel each other out, thus achieving the purpose of weakening or even eliminating the thermal lens effect.

[0013] The corner cube prism is placed on the left side of the multi-stack crystal, its center is on the same horizontal line as the center of the multi-stack crystal, and it is arranged in the vertical direction, that is, its main axis is perpendicular to this horizontal line. Through the optical path folding back and beam homogenization of the corner cube prism, combined with the excellent heat dissipation performance of the multi-stack crystal, it not only ensures the consistency of beam propagation, but also significantly improves the energy distribution uniformity under high-power pumping, which helps to improve the beam quality and operation stability of the laser output.

[0014] The output mirror is placed on the left side of the multi-stack crystal, its center is on the same horizontal line as the center of the multi-stack crystal, and it is parallel to the corner cube prism to form a resonant cavity.

[0015] The cooling device is located below the multi-stack crystal, aiming to dissipate heat efficiently and ensure a stable temperature distribution of the crystal during operation.

[0016] Furthermore, the pump module is used to provide pump energy to the laser gain medium, and a semiconductor laser diode LD, a flash lamp pumping module, or a fiber-coupled pumping module can be selected.

[0017] Furthermore, the multi-stack crystal serves as the laser gain medium, which can effectively absorb pump light and achieve population inversion to generate laser output. The gain layer can be selected from solid laser crystals doped with rare earth elements such as Nd³⁺, Yb³⁺, Er³⁺, such as Nd:YAG, Yb:YAG, Er:YAG, to provide high-efficiency laser gain.

[0018] Furthermore, the cooling device can be selected from a water-cooled heat dissipation device, a static gas conduction cooling device, a flowing air-water hybrid cooling device, or a thermoelectric cooler TEC cooling device.

[0019] Furthermore, by combining the corner cube prism with the multi-stack crystal, the light beam propagates in a uniform "zigzag" path within the resonant cavity, which not only improves the beam shaping and uniformity but also significantly suppresses the wavefront distortion caused by heat. The corner cube prism can compensate for the cavity mirror installation error, improve the mode matching within the cavity at the same time, and cooperate with the transverse heat diffusion structure of the multi-stack crystal to effectively eliminate the problem of beam quality degradation caused by the longitudinal temperature gradient, thereby obtaining high-stability and high-quality output laser.

[0020] An application method of a laser for enhancing the quality of a high-power pump beam based on multi-stack heat transfer, characterized in that the method includes:

[0021] S1: The pump module emits pump light, which is uniformly shaped by the pump shaping and coupling module and then pumps the multi-stack crystal.

[0022] S2: The multi-stack crystal absorbs the pump light to form a population inversion, undergoes stimulated emission, generates laser light. At the same time, combined with the crystal cut angle, the laser light undergoes total internal reflection inside the crystal and stably oscillates in a "zigzag" shape within the resonant cavity composed of the corner cube prism and the output mirror.

[0023] S3: The diamond film in the multi-stack crystal has high thermal conductivity and thermal diffusivity, which quickly conducts the heat deposited in the gain medium due to incomplete pump absorption, quantum deficit, non-radiative transition, and stimulated scattering to the cooling device and takes it away in time, effectively suppressing the formation of the longitudinal temperature gradient. At the same time, the surface roughening eliminates the spontaneous emission oscillation, thereby significantly improving the output beam quality and the operating stability of the laser system.

[0024] S4: Using the corner cube prism as a cavity mirror of the resonant cavity, the special reflection characteristics of the corner cube prism are used to automatically compensate for part of the angular error, which can effectively reduce the energy loss caused by the slight detuning of the cavity mirror. This structure can enhance the mode matching within the cavity, optimize the light field distribution, and improve the light field non-uniformity caused by gain non-uniformity or thermal effects, thereby suppressing mode competition and significantly improving the stability and beam quality of the output beam.

[0025] The laser for enhancing the beam quality of high-power pump based on multi-layer heat transfer provided by the present invention significantly improves the thermal management ability and beam quality control level of the system by combining a multi-layer crystal structure with a corner cube prism. Among them, the multi-layer crystal uses a diamond film with high thermal conductivity to achieve rapid lateral diffusion of heat inside the crystal, extending the heat conduction path, effectively alleviating local heat accumulation and overall temperature rise under high-power working conditions; by precisely designing the number and spatial distribution of the layers, the change of refractive index gradient caused by heat can be effectively suppressed, reducing wavefront distortion and thermal lens effect, thereby improving the stability and consistency of the laser mode; at the same time, as the mirror structure of the resonator cavity, the corner cube prism can not only achieve efficient beam reflection and uniform distribution, but also automatically compensate for slight angular deviation of the cavity mirror, optimizing the mode matching and optical field coupling inside the cavity; the corner cube prism guides the beam to propagate multiple times along a symmetric path, forming a synergistic regulation with the "zigzag" total internal reflection path of the multi-layer crystal, further balancing the heat-affected area and improving the optical field distribution, significantly enhancing the uniformity, stability and TEM 00 mode fidelity of the output beam; this combined structure has good adaptability and scalability, is suitable for various wavelengths, pumping methods and thermal load conditions, helps to realize the miniaturization, high integration and high-performance output of the laser, and meets complex and diverse application requirements.

[0026] (III) Beneficial effects

[0027] Compared with the prior art, the laser for enhancing the beam quality of high-power pump based on multi-layer heat transfer of the present invention has the following beneficial effects:

[0028] In the present invention, through the synergistic combination of the multi-layer crystal and the corner cube prism, the thermal management ability and beam quality control level of the system are significantly improved.

[0029] An ultra-thin diamond film with high thermal conductivity is embedded inside the multi-layer crystal to construct a lateral heat conduction channel, enabling the heat generated during the pumping process to be quickly conducted to the cooling device, significantly reducing heat accumulation, suppressing the thermal lens effect and the change of refractive index gradient, and fundamentally improving the wavefront distortion and the thermal mismatch problem of the laser mode.

[0030] As a cavity mirror component of the resonator cavity, the corner cube prism not only has the function of high-precision reflection on multiple surfaces, but also can adaptively compensate for slight angular deviation of the cavity mirror and optimize the optical field distribution of the resonator cavity.

[0031] Its special reflection path guides the laser to propagate symmetrically in a "zigzag" shape in the multi-layer crystal, further balancing the internal heat load distribution of the crystal, forming a synergistic effect with the multi-layer structure, and effectively enhancing the beam uniformity and system stability.

[0032] While achieving high beam quality output at high power, this combined structure has good structural adjustability and material compatibility. It can flexibly allocate the number of stacked layers, crystal types, and optical cavity parameters according to specific application requirements, and is applicable to high-performance laser systems with different wavelengths, pumping methods, and heat dissipation conditions, providing strong technical support for the integration, compactness, and high-quality output of high-power solid-state lasers. Brief Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the overall structure of a laser for enhancing the beam quality of high-power pump light based on multi-layer heat transfer;

[0034] Figure 2 It is a schematic diagram of the crystal length of the multi-layer heat transfer crystal of the present invention;

[0035] Figure 3 It is a schematic diagram of the structure of the multi-layer heat transfer crystal of the present invention.

[0036] In the figure: 1, pump module; 2, pump shaping and coupling module; 3, multi-layer crystal; 4, corner cube prism; 5, output mirror; 6, cooling device. Detailed Embodiments

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] Embodiment

[0039] As Figure 1 shown, a laser for enhancing the beam quality of high-power pump light based on multi-layer heat transfer includes a pump module 1, a pump shaping and coupling module 2, a multi-layer crystal 3, a corner cube prism 4, an output mirror 5, and a cooling device 6;

[0040] The pump module 1 generates pumping light to excite the multi-layer crystal 3, provides stable energy, and realizes population inversion of the crystal, and is located directly above the multi-layer crystal 3;

[0041] The pump shaping and coupling module 2 is located between the light output port of the pump module 1 and the multi-layer crystal 3, and the pumping light is shaped by the pump shaping and coupling module 2 and then injected into the multi-layer crystal 3;

[0042] The multi-layer crystal 3 is formed by stacking a diamond film and a crystal material. The laser incident surface of the multi-layer crystal 3 is the crystal material with a roughened surface to avoid parasitic oscillation. The interior of the crystal is a diamond film. The end faces of the multi-layer crystal 3 are coated with laser antireflection films, and the other faces are coated with diamond films. The heat deposited inside the multi-layer crystal 3 is transferred along the diamond film in the xz plane to the diamond films in the xy and yz planes outside the crystal, and then to the xz plane at the bottom of the crystal adjacent to the cooling device 6. Finally, the cooling device 6 takes away the heat. The oscillating laser propagates in a "zigzag" shape through total internal reflection inside the multi-layer crystal 3, canceling out the uneven thermal effects in different regions in the y direction, thereby achieving the purpose of weakening or even eliminating the thermal lens effect;

[0043] The corner cube prism 4 is placed on the left side of the multi-layer crystal 3. Its center is on the same horizontal line as the center of the multi-layer crystal 3 and is arranged vertically, that is, its main axis is perpendicular to this horizontal line. Through the optical path folding back and beam homogenization effects, and in cooperation with the excellent heat dissipation performance of the multi-layer crystal 3, the corner cube prism 4 not only ensures the consistency of beam propagation but also significantly improves the energy distribution uniformity under high-power pumping, contributing to the improvement of the beam quality and operation stability of the laser output;

[0044] The output mirror 5 is placed on the left side of the multi-layer crystal 3. Its center is on the same horizontal line as the center of the multi-layer crystal 3 and is parallel to the corner cube prism 4, forming a resonant cavity;

[0045] The cooling device 6 is located below the multi-layer crystal 3, aiming to dissipate heat efficiently and ensure a stable temperature distribution of the crystal during operation;

[0046] Optionally, the pumping module 1 is used to provide pumping energy to the laser gain medium, and semiconductor laser diodes LD, flash lamp pumping modules, fiber-coupled pumping modules, etc. can be selected;

[0047] Optionally, the multi-layer crystal 3 serves as the laser gain medium, which can effectively absorb the pumping light and achieve population inversion to generate laser output. The gain layer can be selected from solid laser crystals doped with rare earth elements such as Nd³⁺, Yb³⁺, Er³⁺, such as Nd:YAG, Yb:YAG, Er:YAG, etc., to provide high-efficiency laser gain;

[0048] Optionally, the cooling device 6 can be selected from water-cooled heat dissipation devices, static gas conduction cooling, flowing air-water hybrid cooling, and cooling devices of thermoelectric coolers TEC. At high power, water cooling is the best cooling method.

[0049] As Figure 2As shown, in the embodiment, there is a fixed geometric relationship between the total length L of the multi-stack crystal and the propagation height h of the light in the crystal. Taking the YAG crystal as an example, assuming its cutting angle is θ1, according to Snell's law in combination with the refractive index relationship between air and the crystal, we can obtain:

[0050]

[0051] From the trigonometric function relationship: θ3 = 90° + θ2 - θ1, θ4 = θ1 - θ2. As Figure 2 shown in the AB segment, the calculated length is:

[0052]

[0053] The calculated lengths of the BC and CD segments are:

[0054]

[0055] The calculated length of the DE segment is:

[0056]

[0057] Setting the total length L of the multi-stack crystal as the length of the AE segment as Figure 2 shown, it can be expressed as:

[0058]

[0059] Among them, n is a natural number, indicating a complete total reflection process of the laser inside the crystal, that is, the crystal length passed is BD. According to the total reflection angle, θ4 is greater than 41.5°. After substituting the parameters and simplifying, the relationship between the total length L and the propagation height h is obtained as:

[0060]

[0061] Among them, θ1 > 72°.

[0062] As Figure 3 shown, in some embodiments, in order to further optimize the multi-stack crystal structure to meet the requirements for beam quality under high-power pumping conditions. As Figure 3 (a) shown, in the modulated pumping laser, the laser peak power is high, and the heat is concentrated on the pumping surface. The number of diamond films with high thermal conductivity is locally increased to reduce the thermal resistance and improve the heat transfer efficiency; as Figure 3 (b) shown, in the continuous pumping laser, due to the continuous pumping of the pumping light, the heat accumulation time is longer. The distribution distance of the diamond films is increased to make the heat distribution more uniform; as Figure 3 (c) shown, it can be used for double-end pumping lasers; as Figure 3As shown in (d), increasing the number of xy-plane thin films can increase the heat transfer efficiency. The optimized multi-stack crystal structure can specifically improve the heat dissipation ability of the crystal, maintain the stability and efficiency of the beam quality under high-power pumping conditions, and lay a solid foundation for the development of high-performance lasers.

[0063] An application method of a laser for enhancing the beam quality of high-power pumping based on multi-stack heat transfer, the method includes:

[0064] S1: The pump module 1 emits pump light, which is uniformly shaped by the pump shaping and coupling module 2 and then pumps the multi-stack crystal 3.

[0065] S2: The multi-stack crystal 3 absorbs the pump light to form a population inversion, undergoes the stimulated emission phenomenon to generate laser light. At the same time, combined with the crystal cutting angle, the laser light undergoes total internal reflection inside the crystal and stably oscillates in a "zigzag" shape in the resonant cavity composed of the corner cube prism 4 and the output mirror 5.

[0066] S3: The diamond thin film in the multi-stack crystal 3 has a high thermal conductivity and thermal diffusivity, which quickly conducts the heat deposited in the gain medium due to incomplete pump absorption, quantum deficit, non-radiative transition, and stimulated scattering to the cooling device 6 and takes it away in time, effectively suppressing the formation of the longitudinal temperature gradient. At the same time, surface roughening eliminates the spontaneous emission oscillation, thus significantly improving the output beam quality and the operation stability of the laser system.

[0067] S4: Using the corner cube prism 4 as a cavity mirror of the resonant cavity, the special reflection characteristics of the corner cube prism 4 can automatically compensate for part of the angular error, effectively reducing the energy loss caused by slight detuning of the cavity mirror. This structure can enhance the mode matching in the cavity, optimize the light field distribution, improve the light field non-uniformity caused by gain non-uniformity or thermal effects, thus suppressing mode competition and significantly improving the stability and beam quality of the output beam.

[0068] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A laser for enhancing the beam quality of a high-power pump based on multi-layer heat transfer, characterized in that, It includes a pump module (1), a pump shaping and coupling module (2), a multi-layer crystal (3), a corner cube prism (4), an output mirror (5), and a cooling device (6). The pump module (1) generates pump light to excite the multi-layer crystal (3), providing stable energy to achieve population inversion of the crystal, and is located directly above the multi-layer crystal (3). The pump shaping and coupling module (2) is located between the light output port of the pump module (1) and the multi-layer crystal (3), and the pump light is shaped by the pump shaping and coupling module (2) and then enters the multi-layer crystal (3). The multi-layer crystal (3) is stacked by crystal material and diamond film. The laser incident surface of the multi-layer crystal (3) is the crystal material with roughened surface to avoid parasitic oscillation. The inside of the crystal is diamond film. The end faces of the multi-layer crystal (3) are coated with laser antireflection film, and the other faces are coated with diamond film to facilitate the rapid removal of the crystal heat. The oscillating laser propagates in a "zigzag" shape through total internal reflection inside the multi-layer crystal (3), so that the uneven thermal effects in different regions in the y direction cancel each other out, thereby achieving the purpose of weakening or even eliminating the thermal lens effect. The corner cube prism (4) is placed on the left side of the multi-layer crystal (3), its center is on the same horizontal line as the center of the multi-layer crystal (3), and it is arranged in the vertical direction, that is, its main axis is perpendicular to this horizontal line. Through the optical path folding back and beam homogenization effect of the corner cube prism (4), combined with the excellent heat dissipation performance of the multi-layer crystal (3), it not only ensures the consistency of beam propagation, but also significantly improves the energy distribution uniformity under high-power pumping, which helps to improve the beam quality and operation stability of the laser output. The output mirror (5) is placed on the left side of the multi-layer crystal (3), its center is on the same horizontal line as the center of the multi-layer crystal (3), and is parallel to the corner cube prism (4) to form a resonant cavity. The cooling device (6) is located below the multi-layer crystal (3), aiming to dissipate heat efficiently and ensure a stable temperature distribution of the crystal during operation.

2. The laser for enhancing the quality of a high-power pump beam based on multi-layer heat transfer according to claim 1, wherein The pump module (1) is used to provide pump energy to the laser gain medium, and semiconductor laser diode LD, flash lamp pump module, and fiber-coupled pump module can be selected.

3. The laser for enhancing the quality of a high-power pump beam based on multi-layer heat transfer according to claim 1, wherein The multi-layer crystal (3) serves as the laser gain medium, which can effectively absorb pump light and achieve population inversion to generate laser output. The gain layer can be selected from solid laser crystals doped with rare earth elements such as Nd³⁺, Yb³⁺, Er³⁺, such as Nd:YAG, Yb:YAG, Er:YAG, to provide high-efficiency laser gain.

4. The laser for enhancing the beam quality of a high-power pump based on multi-layer heat transfer according to claim 1, characterized in that The cooling device (6) can be selected from water-cooled heat dissipation devices, static gas conduction cooling, flowing air-water hybrid cooling, and cooling devices with thermoelectric cooler TEC.

5. The laser for enhancing the high-power pump beam quality based on multi-stack heat transfer according to claim 1, characterized in that By combining and applying a corner cube prism (4) with a multi-stack crystal (3), the light beam propagates in a uniform "zigzag" path within the resonant cavity, which not only improves the beam shaping and uniformity but also significantly suppresses the wavefront distortion caused by heat. The corner cube prism (4) can compensate for the cavity mirror installation error and simultaneously improve the mode matching within the cavity. Combining with the transverse heat diffusion structure of the multi-stack crystal (3), it effectively eliminates the problem of beam quality degradation caused by the longitudinal temperature gradient, thereby obtaining high-stability and high-quality output laser.

6. The application method of the laser for enhancing the high-power pump beam quality based on multi-layer heat transfer according to any one of claims 1-5, characterized in that Including: S1: The pump module (1) emits pump light, which is uniformly shaped by the pump shaping and coupling module (2) and then pumps the multi-stack crystal (3); S2: The multi-stack crystal (3) absorbs the pump light to form population inversion, undergoes the stimulated emission phenomenon to generate laser. At the same time, combined with the crystal cut angle, the laser undergoes total internal reflection inside the crystal and stably oscillates in a "zigzag" manner within the resonant cavity composed of the corner cube prism (4) and the output mirror (5); S3: The diamond film in the multi-stack crystal (3) has high thermal conductivity and thermal diffusivity, which quickly conducts the heat deposited in the gain medium due to incomplete pump absorption, quantum deficit, non-radiative transition, and stimulated scattering to the cooling device (6) and takes it away in time, effectively suppressing the formation of the longitudinal temperature gradient. At the same time, the surface roughening eliminates the spontaneous emission oscillation, thereby significantly improving the output beam quality and the operating stability of the laser system; S4: Using the corner cube prism (4) as the resonant cavity mirror, the special reflection characteristics of the corner cube prism (4) are used to automatically compensate for part of the angular error, which can effectively reduce the energy loss caused by the slight detuning of the cavity mirror. This structure can enhance the mode matching within the cavity, optimize the light field distribution, and improve the light field non-uniformity caused by gain non-uniformity or thermal effects, thereby suppressing mode competition and significantly improving the stability and beam quality of the output beam.

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