Rod-shaped laser gain medium with radial concentration gradient distribution and preparation method thereof

Abstract

The invention discloses a rod-like laser gain medium with radial concentration gradient distribution and a preparation method thereof, and belongs to the technical field of laser materials. Aiming at the thermal lens effect problem caused by Gaussian pump light in a high-power solid laser, the heat effect is inhibited through a material design source. Active ions of the gain medium are transition metal ions, a matrix material is a chalcogenide, the radial doping concentration of the gain medium is in high-low-high gradient distribution, Gaussian pump light intensity distribution is matched, and axis heat production is reduced. The preparation method comprises the steps of machining, transition metal film deposition, high-temperature diffusion and end face polishing. According to the design, the heat effect under high power is obviously inhibited, the light beam quality factor M2 is stabilized at 1.1-1.3, and the light-to-light conversion efficiency is obviously improved. The method is simple in process, low in cost and suitable for industrial production, and can be widely applied to the fields of high-power lasers, medical equipment, industrial processing and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of laser materials, and in particular to a rod-shaped laser gain medium with radial concentration gradient distribution and a preparation method thereof. Background Art

[0002] In recent years, high-power all-solid-state lasers have been widely used in various fields, demonstrating enormous development potential. In the military, they are used for laser guidance and laser weapons; in the medical field, they enable high-precision surgical treatment and disease diagnosis; and in industrial processing, they play an important role in cutting, welding, and surface treatment. However, the thermal effects of the laser gain medium have become a key factor limiting the further increase of laser power. Heat generation in the laser gain medium primarily stems from quantum defects, concentration quenching, and heat absorption by the working material of the pump light. For high-energy solid-state lasers, high pump powers generate significant heat within the laser gain medium, while external heat dissipation from the medium's surface leads to uneven temperature distribution within the medium. While using Gaussian light as a pump source in rod-shaped laser gain media improves laser output beam quality and suppresses higher-order modes, it also results in significantly greater heat generation at the center of the laser gain medium than at the edges. Furthermore, cooling devices for the laser gain medium typically only cool the outer surface, resulting in a misalignment between the heat generation and heat dissipation centers, ultimately forming a temperature gradient thermal lens that severely impacts solid-state laser performance.

[0003] In a rod laser, the geometric matching of the Gaussian pump light (spot radius ω0 = 0.1-1 mm) and the rod-shaped medium results in a unique thermal distribution: (1) Radial temperature gradient: The pump light intensity is maximum at the axis (I(r) = I0exp(-2r 2 / ω0 2 )), the heat generation rate q(r)∝I(r), forming a central high temperature zone. (2) Axial inhomogeneity: The exponential attenuation of the pump light in the medium (absorption coefficient α=1-10cm -1) causes the axial temperature distribution to be Gaussian, which is superimposed with the radial gradient to form a three-dimensional thermal distortion field. (3) Thermal stress coupling: The temperature gradient causes thermal expansion difference, which generates radial compressive stress and circumferential tensile stress inside the medium. When the circumferential tensile stress exceeds the fracture strength of the material, it will cause crack initiation. For rod-shaped laser gain media, using Gaussian light as a pump source is beneficial to improving the beam quality of the laser output, suppressing high-order modes, and thus improving the beam quality of the output laser. However, this makes the heat generation at the axial center of the laser gain medium much greater than that at the edge. The cooling device for the laser gain medium can generally only cool the outer surface of the gain medium, which causes the inconsistency between the heat generation center and the heat dissipation center, thereby causing the formation of a temperature gradient thermal lens. Among the many factors that affect the light field of a solid-state laser, the temperature gradient usually accounts for up to 80%. Therefore, finding new methods to suppress the influence of the radial temperature gradient distribution of the material under Gaussian light pumping on the performance of solid-state lasers is the focus of research on solving thermal effects and is of great significance.

[0004] In terms of compensating for the thermal lens effect, CN113381276A discloses a laser crystal thermal lens effect self-compensation device, but the dual-resonance cavity structure needs to accurately match the optical parameters of the two cavities (such as cavity length and curvature radius), which increases the difficulty of debugging and manufacturing costs. In industrial-scale production, the assembly yield of the dual-cavity structure may be lower than that of the single-cavity design, limiting its promotion and application. CN113381276A discloses a laser crystal thermal lens effect self-compensation device, but the device relies on a mechanical moving mechanism to adjust the lens position, and the response time is 10-100ms, which cannot adapt to the real-time thermal changes of high repetition rate (>1kHz) pulsed lasers. In terms of concentration gradient doped laser gain media, CN117209275A discloses a concentration gradient doped laser transparent ceramic and its preparation method. The patent prepares LuAG ceramics by gel injection molding. The actual doping curve of the cast slurry concentration changes in a step-like manner, which cannot match high-light pumping to reduce thermal effects. Summary of the Invention

[0005] The present invention aims to solve the above technical problems and provide a rod-shaped laser gain medium with radial concentration gradient distribution and a preparation method thereof, which has a short preparation cycle, a simple process and can be industrialized.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a rod-shaped laser gain medium with radial concentration gradient distribution, wherein the activation ion of the rod-shaped laser gain medium is a transition metal ion Ti 2+ Cr 2+ 、Fe 2+ 、Co 2+ 、Ni 2+One or more of the above, the matrix material of the rod-shaped laser gain medium is selected from chalcogenides, including binary compounds ZnSe, CrSe, ZnS, ZnTe, CdSe, and ternary compounds CdMnTe, CdZnTe, ZnSSe, and ZnMgSe. The transition metal ion doping concentration on both end faces of the rod-shaped laser gain medium exhibits a symmetrical or asymmetrical distribution characteristic along the radial direction, first decreasing and then increasing from the central region to the edge region, thereby forming a pump matching structure with low absorption at the center and high absorption at the edge. The gradient distribution matches the heat generation rate in the axial region with the heat dissipation capacity of the edge region, thereby suppressing the thermal lens effect.

[0008] The concentration distribution satisfies the following function:

[0009]

[0010] C(x,t) is the concentration at position x at time t, C left and C right are the concentrations at the left and right edges, respectively, D is the diffusion coefficient, L is the diameter of the material, and erfc is the complementary error function.

[0011] Furthermore, the diameter of the rod-shaped laser gain medium is 0.5 to 2 mm.

[0012] Furthermore, the doping concentration of the activated ions is 10 17 ~10 20 ions / cm 3 .

[0013] Furthermore, the beam quality factor M of the rod-shaped laser gain medium when the output power is less than 10W 2 Stable at 1.1~1.3.

[0014] Furthermore, the doping concentration distribution makes the absorption rate of the pump light in the central region 5%-30% lower than that in the edge region.

[0015] The present invention also provides a method for preparing the above-mentioned rod-shaped laser gain medium with radial concentration gradient distribution, which mainly comprises the following steps:

[0016] S1: machining the laser gain medium into a cylindrical shape, i.e., a rod-shaped laser gain medium, and performing polishing and cleaning treatment;

[0017] S2: Depositing transition metal ions uniformly in the form of a thin film on the side of the rod-shaped laser gain medium;

[0018] S3: The coated rod-shaped laser gain medium is sealed in a quartz tube, evacuated and placed in a tube furnace for temperature diffusion treatment;

[0019] S4: polishing both end faces of the rod-shaped laser gain medium after the temperature diffusion treatment to obtain a rod-shaped laser gain medium with a radial concentration gradient distribution.

[0020] Furthermore, in step S2, the thickness of the transition metal film is 500 to 2000 nm.

[0021] Furthermore, in step S3, the vacuum degree in the quartz tube is 10 -5 Pa-10 -3 Pa.

[0022] Furthermore, in step S3, the temperature of the temperature diffusion treatment is 600-1000° C., and the diffusion time is 100-500 hours.

[0023] Furthermore, in step S4, the end surface roughness after polishing is ≤1 nm.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The inherent concentration gradient of the rod-shaped laser gain medium prepared by this invention can well match the energy distribution of Gaussian pump light, effectively reducing central heat accumulation and ensuring that the heat generation rate in the axial region matches the heat dissipation capacity of the edge region. This significantly suppresses the laser thermal lensing effect from the source of material design, eliminating the need for external compensation mechanisms and significantly improving the light-to-light conversion efficiency of the laser output.

[0026] (2) The rod-shaped laser gain medium prepared by the present invention optimizes the refractive index field distribution through the gradient distribution of concentration, significantly reduces the thermally induced wavefront distortion, suppresses the generation of high-order modes, and is conducive to generating higher beam quality.

[0027] (3) By combining thin film deposition with high-temperature diffusion, continuous concentration gradient control can be achieved with only a single diffusion, resulting in a short preparation cycle. By regulating the diffusion parameters, the gradient distribution function can be precisely designed to accommodate different pump power requirements, which can be applied to the industrial production of laser gain medium materials.

[0028] (3) The combination of activated ions and chalcogenide matrix has both a wide absorption bandwidth (covering the 1-3 μm mid-infrared band) and a high damage threshold (>10 GW / cm 2 ), which can be adapted to various solutions such as fiber pumping and direct diode pumping. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a radial distribution diagram of doping ion concentration of the sample prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Example 1:

[0032] The ZnS crystal material was machined into a cylinder with a diameter of 0.5 mm and then polished and cleaned. A transition metal chromium film was evenly deposited on the side of the rod-shaped material with a deposition thickness of 500 nm. The sample was placed in a quartz tube and vacuumed to a vacuum degree of 10 -5 Pa was placed in a tube furnace for diffusion at 980°C for 100 hours. After polishing both end faces, a rod-shaped laser gain medium with a radial concentration gradient distribution was obtained. The end face roughness after polishing was 1 nm. The absorption rate of the pump light in the axis area was 12% lower than that in the edge area. Figure 1 As shown in the figure, the doping ion concentration distribution of the prepared sample in the radial direction shows that the transition metal ion doping concentration at both end faces of the rod-shaped laser gain medium increases from 3.92×10 18 ions / cm 3 Decreased to 0.95×10 18 ions / cm 3 , and then increased again to 3.9×10 18 ions / cm 3 , thus forming a pump matching structure with low absorption in the center and high absorption at the edge, which was placed vertically into the laser resonator for laser experiments, with an output power of 10W and a beam quality factor of M 2 is 1.2. , Example 2:

[0033] The ZnS crystal material was machined into a cylinder with a diameter of 2 mm and then polished and cleaned. A transition metal chromium film was evenly deposited on the side of the rod-shaped material with a deposition thickness of 2000 nm. The sample was placed in a quartz tube and vacuumed to a vacuum degree of 10 -4 Pa, placed in a tube furnace for diffusion at 940°C for 500 hours. After polishing both end faces, a rod-shaped laser gain medium with a radial concentration gradient distribution was obtained. The end face roughness after polishing was 0.87nm. The absorption rate of the pump light in the axis area was 27% lower than that in the edge area. It was placed vertically into the laser resonator for laser experiments. The beam quality factor M was 4W when the output power was 4W. 2 is 1.12.

[0034] Example 3:

[0035] The ZnSe crystal material was machined into a cylinder with a diameter of 0.5 mm and then polished and cleaned. A transition metal chromium film was evenly deposited on the side of the rod-shaped material with a deposition thickness of 1000 nm. The sample was placed in a quartz tube and vacuumed to a vacuum degree of 10 -3Pa, placed in a tube furnace for diffusion at 800°C for 100 hours. After polishing both end faces, a rod-shaped laser gain medium with a radial concentration gradient distribution was obtained. The roughness of the polished end face was 0.72nm. The absorption rate of the pump light in the axis area was 5% lower than that in the edge area. It was placed vertically in the laser resonator for laser experiments. The beam quality factor M was 5.4W when the output power was 5.4W. 2 is 1.1.

[0036] Example 4:

[0037] The ZnSe crystal material was machined into a cylinder with a diameter of 2 mm and then polished and cleaned. A transition metal iron film was evenly deposited on the side of the rod-shaped material with a deposition thickness of 500 nm. The sample was placed in a quartz tube and vacuumed to a vacuum degree of 10 -3 Pa, placed in a tube furnace for diffusion at 1000°C for 200 hours. After polishing both end faces, a rod-shaped laser gain medium with a radial concentration gradient distribution was obtained. The roughness of the polished end face was 0.9nm. The absorption rate of the pump light in the axis area was 10% lower than that in the edge area. It was placed vertically into the laser resonator for laser experiments. The beam quality factor M was 3W at an output power of 3W. 2 is 1.25.

[0038] Example 5:

[0039] The ZnSe crystal material was machined into a cylinder with a diameter of 1 mm and then polished and cleaned. A transition metal iron film was evenly deposited on the side of the rod-shaped material with a deposition thickness of 1500 nm. The sample was placed in a quartz tube and vacuumed to a vacuum degree of 10 -5 Pa, placed in a tube furnace for diffusion at 1000°C for 500 hours. After polishing both end faces, a rod-shaped laser gain medium with a radial concentration gradient distribution was obtained. The roughness of the polished end face was 0.57nm. The absorption rate of the pump light in the axis area was 13% lower than that in the edge area. It was placed vertically in the laser resonator for laser experiments. The beam quality factor M was 0.7W at an output power of 0.7W. 2 is 1.3.

[0040] Example 6:

[0041] The ZnSSe crystal material was machined into a cylinder with a diameter of 0.5 mm and then polished and cleaned. A transition metal iron film was evenly deposited on the side of the rod-shaped material with a deposition thickness of 2000 nm. The sample was placed in a quartz tube and vacuumed to a vacuum degree of 10 -5Pa, placed in a tube furnace for diffusion at a temperature of 1000°C, placed in a tube furnace for temperature diffusion for 300 hours, and polished both end faces to obtain a rod-shaped laser gain medium with a radial concentration gradient distribution. The polished end face roughness is 0.98nm. The absorption rate of the axial region to the pump light is 30% lower than that of the edge region. It is placed vertically into the laser resonator for laser experiments, with an output power of 0.5W and a beam quality factor M 2 is 1.2.

[0042] Example 7:

[0043] The CdSe crystal material was machined into a cylinder with a diameter of 1.5 mm and then polished and cleaned. A transition metal chromium film was evenly deposited on the side of the rod-shaped material with a deposition thickness of 2000 nm. The sample was placed in a quartz tube and vacuumed to a vacuum degree of 10 -4 Pa, placed in a tube furnace for diffusion at 850°C for 500 hours. After polishing both end faces, a rod-shaped laser gain medium with a radial concentration gradient distribution was obtained. The end face roughness after polishing was 0.56nm. The absorption rate of the pump light in the axis area was 22% lower than that in the edge area. It was placed vertically in the laser resonator for laser experiments, with an output power of 2W and a beam quality factor M. 2 It is 1.27.

[0044] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A rod-shaped laser gain medium with radial concentration gradient distribution, characterized in that: The activation ions of the rod-shaped laser gain medium are transition metal ions selected from Ti 2+ Cr 2+ 、Fe 2+ 、Co 2+ 、Ni 2+ At least one of the above, the matrix material of the rod-shaped laser gain medium is a chalcogenide compound selected from the binary compounds ZnSe, CrSe, ZnS, ZnTe, CdSe or the ternary compounds CdMnTe, CdZnTe, ZnSSe, and ZnMgSe, and the transition metal ion doping concentration on both end faces of the rod-shaped laser gain medium exhibits a symmetrical or asymmetrical distribution characteristic in the radial direction, first decreasing and then increasing from the central region to the edge region, thereby forming a pump matching structure with low absorption at the center and high absorption at the edge, and the concentration distribution satisfies the following function: C(x,t) is the concentration at position x at time t, C left and C right are the concentrations at the left and right edges respectively, D is the diffusion coefficient, L is the diameter of the material, erfc is the complementary error function, and the gradient distribution makes the heat generation rate in the axial area match the heat dissipation capacity of the edge area, thereby suppressing the thermal lens effect.

2. The rod-shaped laser gain medium with radial concentration gradient distribution according to claim 1, characterized in that: The diameter of the rod-shaped laser gain medium is 0.5-2 mm.

3. The rod-shaped laser gain medium with radial concentration gradient distribution according to claim 1, characterized in that: The doping concentration of the activated ions is 10 17 ~10 20 ions / cm 3 .

4. The rod-shaped laser gain medium with radial concentration gradient distribution according to claim 1, characterized in that: The beam quality factor M of the rod-shaped laser gain medium when the output power is less than 10W 2 Stable at 1.1~1.

3.

5. The rod-shaped laser gain medium with radial concentration gradient distribution according to claim 1, characterized in that: The doping concentration distribution makes the absorption rate of the pump light in the axial core region 5%-30% lower than that in the edge region.

6. A method for preparing a rod-shaped laser gain medium with a radial concentration gradient distribution according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: machining the laser gain medium into a cylindrical shape, i.e., a rod-shaped laser gain medium, and performing polishing and cleaning treatment; S2: Depositing transition metal ions uniformly in the form of a thin film on the side of the rod-shaped laser gain medium; S3: The coated rod-shaped laser gain medium is sealed in a quartz tube, evacuated and placed in a tube furnace for temperature diffusion treatment; S4: polishing both end faces of the rod-shaped laser gain medium after the temperature diffusion treatment to obtain a rod-shaped laser gain medium with a radial concentration gradient distribution.

7. The method for preparing a rod-shaped laser gain medium with a radial concentration gradient distribution according to claim 6, characterized in that: The thickness of the transition metal film prepared in step S2 is 500 to 2000 nm.

8. The method for preparing a rod-shaped laser gain medium with a radial concentration gradient distribution according to claim 6, wherein: In step S3, the vacuum degree in the quartz tube is 10 -5 Pa-10 -3 Pa, the temperature diffusion treatment has a temperature of 600-1000° C. and a diffusion time of 100-500 h.

9. The method for preparing a rod-shaped laser gain medium with radial concentration gradient distribution according to claim 6, characterized in that: In step S4, the end surface roughness after polishing is ≤1nm.

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