Semiconductor side-pumped solid laser module based on composite reflective condensation cavity

Abstract

The invention belongs to the technical field of semiconductor laser pumping solid lasers, and discloses a semiconductor side pumping solid laser module based on a composite reflection light-gathering cavity, which comprises an LD bar (1) and a thin rod type laser working medium (3) arranged in the composite reflection light-gathering cavity (2), pump light emitted by a light-emitting point of the LD bar (1) is reflected by the oval inner wall of the upper half portion of the composite reflection light-gathering cavity (2) and then is totally gathered at the axis position of the thin rod type laser working medium (3), and residual pump light absorbed by the thin rod type laser working medium (3) reaches the semicircular inner wall of the lower half portion of the right side of the composite reflection light-gathering cavity (2). And the residual pump light energy is reflected back to the thin rod type laser working medium (3) by the original path, so that the residual pump light energy is absorbed again, and high-efficiency pumping is realized. According to the invention, pumping with extremely high geometrical optical efficiency is realized for a thin rod type laser working medium, and the utilization efficiency of pumping light energy is improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser-pumped solid-state laser technology, and relates to a semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity. Background Technology

[0002] Semiconductor-pumped solid-state lasers have advantages over traditional flash lamp-pumped solid-state lasers, including high electro-optical efficiency, less waste heat, small size, light weight, high output power, good beam quality, and long lifespan. They are widely used in industrial, medical, and military fields.

[0003] Based on the relative relationship between the laser emission direction and the pump light incident direction, semiconductor-pumped solid-state lasers are generally classified into two types: end-pumped and side-pumped. Each of these pumping methods has its own characteristics, advantages, and disadvantages. End-pumping is typically suitable for laser working media with a small aspect ratio and a high laser oscillation threshold, while side-pumping is typically suitable for laser working media with a large aspect ratio and a low laser oscillation threshold. End-pumping generally yields better beam quality, while side-pumping generally yields higher output power.

[0004] For certain highly doped laser working media with high quantum defects, such as holmium-doped fluoride crystals that output mid-infrared lasers, the waste heat generated by laser oscillation is relatively large. The shape of the laser working medium needs to be designed as a thin rod with a diameter of about 1 mm, and combined with efficient side cooling, in order to avoid the fatal impact on laser output performance caused by thermal stress due to internal temperature gradient, such as thermal lensing, thermal birefringence, and thermal cracking.

[0005] However, for such highly doped, high-quantum-defect thin rod-shaped laser working media, traditional end-face and side-pumping methods are difficult to implement. The high doping characteristics of this type of laser working medium result in a very high absorption coefficient for pump light. If end-face pumping is used, the absorption of the pump light will be concentrated near the incident end, while other parts of the laser working medium will have almost no pump absorption, making it difficult to generate laser oscillation. If side-pumping is used, due to the very small diameter of this type of laser working medium, most of the pump light will not be able to enter the laser working medium, resulting in very low geometric optical efficiency and making it difficult to generate laser oscillation. Attempting to focus the side-pump light onto the thin rod-shaped laser working medium using a lens is extremely difficult due to the immense challenges in lens fabrication and assembly, making it practically impossible. Summary of the Invention

[0006] (a) Purpose of the invention To achieve efficient side pumping of highly doped, high-quantum-defect thin rod-shaped laser working media, enabling it to generate high-performance laser output, a semiconductor-side-pumped solid-state laser module suitable for such thin rod-shaped laser working media is provided.

[0007] (II) Technical Solution To address the aforementioned technical problems, this invention provides a semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity. It uses a linear array semiconductor laser diode bar (hereinafter referred to as LD bar) as the pump source, leveraging its near-point light source emission characteristics within the divergence angle range of the fast-axis emission direction. An elliptical-semi-circular composite reflective focusing cavity is employed, utilizing its unique geometric optical properties to maximize the absorption of the pump light energy emitted from the LD bar by the thin rod-shaped laser working medium, thus achieving efficient pumping.

[0008] The semiconductor side-pumped solid-state laser module of the present invention includes: LD bar 1, composite reflective focusing cavity 2, and thin rod-shaped laser working medium 3; LD bar 1 and thin rod-shaped laser working medium 3 are arranged in the composite reflective focusing cavity 2. The pump light emitted from the emitting point of LD bar 1 is reflected by the elliptical inner wall of the upper half of the composite reflective focusing cavity 2 and then converges at the axial position of the thin rod-shaped laser working medium 3. The residual pump light after being absorbed by the thin rod-shaped laser working medium 3 reaches the semi-circular inner wall of the lower right half of the composite reflective focusing cavity 2 and is reflected back to the thin rod-shaped laser working medium 3, so that the residual pump light energy is absorbed again, thereby achieving efficient pumping.

[0009] LD bar1 is a linear array of semiconductor laser diodes that provides a pump source for the laser. Its fast axis divergence angle is parallel to the XY plane in the figure.

[0010] The function of the composite reflective focusing cavity 2 is to reflect and converge the pump light emitted by the LD bar 1, enabling the thin rod-shaped laser working medium 3 to be efficiently pumped. The inner wall of the composite reflective focusing cavity 2 can be divided into three regions based on its function and structure, such as... Figure 4 As shown: ① The upper half of the cavity inner wall is semi-elliptical in shape, with the left and right foci of the ellipse being the emitting point of LD bar1 and the axis of the thin rod-shaped laser working medium 3, respectively. This region of the cavity inner wall has high surface accuracy and flatness, resulting in high reflectivity for the pump light. ② The lower right half of the cavity inner wall is semi-circular in shape, with its center coinciding with the right focus of the ellipse, which is the axis of the thin rod-shaped laser working medium 3. The diameter of the semicircle is the difference between the major axis and the focal length of the ellipse (2a-2c). Figure 5 As shown; the inner wall of the cavity in this area has high surface accuracy and flatness, and high reflectivity for pump light. ③ The lower left half of the inner wall of the cavity is irregularly shaped, and its inner wall has no reflective function. There are no requirements for surface shape and reflectivity. It mainly serves as structural support and cavity enclosure.

[0011] The diameter of the thin rod-shaped laser working medium 3 is much smaller than that of a conventional cylindrical laser working medium, typically about 1 mm, and its axis is parallel to... Figure 2 and Figure 3 The Z-axis direction, whose axis is located at the right focus of the elliptical region of the composite reflective concentrator cavity 2, as shown in the figure. Figure 5 As shown. To avoid the impact of spontaneous emission (ASE) on laser output performance, the side surface of the thin rod-shaped laser working medium 3 is roughened to a semi-transparent surface. Therefore, in addition to absorption, reflection, and transmission of pump light, it also exhibits some diffuse reflection and transmission. The thin rod-shaped laser working medium 3 is surrounded by a glass sleeve 5 concentric with it. The gap between the two is filled with flowing coolant 4 to cool the thin rod-shaped laser working medium 3. The inner and outer surfaces of the glass sleeve 5 are coated with anti-reflection films that are sensitive to the pump light wavelength, and the glass sleeve 5 itself has a very low absorption coefficient for pump light. The coolant inlet and outlet 6 are connected to external water-cooling equipment. The total reflection mirror 7 and output mirror 8 of the laser resonator are located outside the composite reflective focusing cavity 2 and are coaxial with the thin rod-shaped laser working medium 3.

[0012] The working principle of this invention is as follows: Figure 5 As shown, in the XY plane, the emitting point of LD bar1 and the axis of the thin rod-shaped laser working medium 3 are located at the left and right focal points of the ellipse in the upper half of the composite reflective focusing cavity 2, respectively. The fast-axis divergence direction of LD bar1 is also in the XY plane, and the center of the fast-axis divergence angle points towards... Figure 5 Upper right. Based on the geometric optical properties of an ellipse (light rays emitted from one focus of an ellipse must pass through the other focus of the ellipse after reflection at the boundary of the ellipse), and the fact that the luminous point of LD bar1 approximates the luminous characteristics of a point source within the fast axis divergence angle range, and ignoring the divergence in the slow axis divergence angle direction, the pump light emitted from the luminous point of LD bar1 passes through the upper half of the elliptical inner wall of the composite reflective focusing cavity 2 ( Figure 4 After reflection from region ①, the light will pass through the glass sleeve 5 and coolant 4 in sequence, and converge entirely at the axial position of the thin rod-shaped laser working medium 3. Since the diameter of the thin rod-shaped laser working medium 3 is very small, the diffuse reflection and transmission of the pump light from its roughened side surface can be approximated as originating from its axial position throughout the pump light path. Based on the geometric optical properties of a circle (light emitted from the center of the circle will inevitably pass back through the center after reflection at the circle's boundary), the residual pump light (containing both transmitted and diffusely transmitted pump energy) absorbed by the thin rod-shaped laser working medium 3 will pass through the coolant 4 and glass sleeve 5 in sequence, reaching the inner wall of the semi-circular lower right half of the composite reflective focusing cavity 2. Figure 4 The residual pump light energy is absorbed again in region ② and reflected back to the thin rod-shaped laser working medium 3, thus achieving efficient pumping.

[0013] (III) Beneficial Effects The semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity provided by the above technical solution has the following beneficial effects: (1) Based on the geometric optical properties of ellipse and circle, and the light emission characteristics of LD bar approximating point light source in the fast axis divergence angle range, the composite reflective focusing cavity designed in this invention can achieve extremely high geometric optical efficiency pumping of thin rod-shaped laser working medium, improve the utilization efficiency of pump light energy, and reduce the volume, weight and power consumption of the laser pump part under the same laser output power; at the same time, it reduces the waste heat generation of the pump part, reduces the pressure on the temperature control system, and improves the system reliability and environmental adaptability of the entire laser.

[0014] (2) The present invention has a simple and reliable structure. The manufacturing process of the composite reflective focusing cavity can refer to and follow the traditional manufacturing process of the elliptical reflective focusing cavity of the flash lamp pump rod laser working medium, or modify the existing elliptical reflective focusing cavity to reduce the manufacturing difficulty and cost. Attached Figure Description

[0015] Figure 1 This is a cross-sectional view of the XY plane of a semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity according to the present invention.

[0016] Figure 2 yes Figure 1 3D structural view.

[0017] Figure 3 yes Figure 1 YZ plane cross-sectional structural view.

[0018] Figure 4 This is a functional structural partition diagram of the inner wall of a composite reflective focusing cavity.

[0019] Figure 5 yes Figure 1 The diagram illustrates the working principle of the ellipse, where a, b, and c represent the major semi-axis, minor semi-axis, and semi-focal length of the ellipse, respectively.

[0020] Figure 6 This is a magnified view of a portion of the LD bar luminescent slit. Detailed Implementation

[0021] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0022] like Figures 1 to 6As shown, the semiconductor side-pumped solid-state laser module based on the composite reflective focusing cavity in this embodiment includes a composite reflective focusing cavity 2 whose inner wall can be divided into three different functional structural regions, as well as LD bar1 and thin rod-shaped laser working medium 3 located at the left and right focal positions of the semi-elliptical region of the composite reflective focusing cavity 2, respectively.

[0023] Among them, the composite reflective focusing cavity 2 is a metal cavity, and its inner wall is divided into three regions according to different functions and structures, such as... Figure 4 In the XY plane shown: Region ① is located in the upper half of the entire cavity, and is semi-elliptical in shape. The inner wall of this region must have high reflectivity for the pump light. Therefore, during processing, it is necessary to ensure high surface accuracy and flatness, and a high-reflectivity film layer for the pump wavelength needs to be deposited on the inner wall or other methods should be used to improve its reflectivity. Region ② is located in the lower right part of the entire cavity, and is semi-circular in shape. The inner wall of this region must also have high reflectivity for the pump light. Therefore, during processing, it is necessary to ensure high surface accuracy and flatness, and a high-reflectivity film layer for the pump wavelength needs to be deposited on the inner wall or other methods should be used to improve its reflectivity. At the same time, the connection between Region ② and Region ① must be smooth and flat. Therefore, the center of Region ② needs to precisely coincide with the right focal point of Region ①, and the diameter of Region ② must be exactly equal to the difference between the major axis and the focal length of Region ① (2a-2c). Figure 5 As shown. Region ③ is located in the lower left part of the entire cavity. Its inner wall has no reflective function, and there are no requirements for its surface shape and reflectivity. It mainly serves as structural support and cavity enclosure. Without affecting the pump optical path, its specific shape can be adjusted according to the installation and fixing requirements of LD bar1 and other components.

[0024] The composite reflective focusing cavity 2 can be manufactured using two methods: integral manufacturing and split manufacturing. Integral manufacturing involves machining or casting the entire focusing cavity entity, including regions ①, ②, and ③, in one step, followed by surface treatment of the inner walls of each region. Split manufacturing involves machining the focusing cavity entities corresponding to regions ①, ②, and ③ separately, treating the inner wall surfaces of each part, and then assembling or welding them together. If split manufacturing is used, a traditional elliptical focusing cavity with suitable dimensions and inner wall reflectivity can be selected, divided into two equal parts along the YZ plane, and either part can be used as region ①. The assembly or welding process must ensure the positional accuracy of the three parts (regions ①, ②, and ③) and the smoothness and flatness of the joints, while also avoiding affecting the inner wall surface shape and reflectivity of regions ① and ②.

[0025] Among them, LD bar1 is the pump source of the laser, and its installation position and angle should refer to... Figure 5In the XY plane, its luminous point is located at the left focal point of region ① of the composite reflective focusing cavity 2, and the center of its fast axis divergence angle points towards... Figure 5 The upper right corner is positioned so that as much pump light as possible, after reflection from the inner surface of region ①, converges at the right focal point. Because... Figure 5 The pump light path is reversible. If the emitting point of LD bar1 is strictly located at the left focal point of region ① of the composite reflective focusing cavity 2, the residual pump light after being absorbed twice by the thin rod-shaped laser working medium 3 will return along the same path and converge at the emitting point of LD bar1. This could potentially damage the internal light-emitting element of LD bar1. To avoid this situation, LD bar1 should be finely adjusted during installation so that its emitting point position (emitting slit) is slightly offset from the left focal point of region ① of the composite reflective focusing cavity 2. The offset distance is approximately equal to the width of the emitting slit (approximately 0.1 mm). Figure 6 As shown. Since the width of the emitting slit in LD bar1 is about an order of magnitude smaller than the diameter of the thin rod-shaped laser working medium 3, the above measures can both prevent residual pump light from returning and converging into the emitting slit of LD bar1, and also... Figure 5 The impact on the pump optical path is minimal, and it can still ensure efficient pumping of the thin rod-shaped laser working medium 3.

[0026] The installation and fixing positions of the thin rod-shaped laser working medium 3 and the glass sleeve 5 should ensure that, in the XY plane, their centers coincide and are located at the right focal point of region ① of the composite reflective focusing cavity 2, and that there is a gap between them that allows the coolant 4 to flow rapidly. The Z-direction length of the glass sleeve 5 is slightly shorter than that of the thin rod-shaped laser working medium 3. Both ends of the glass sleeve 5 in the Z-direction must be strictly sealed to ensure that the coolant 4 does not leak into the composite reflective focusing cavity 2. The glass sleeve 5 should have coolant inlet and outlet 6 at both ends. Figure 3 As shown, an external temperature-controlled liquid cooling system can be connected and adjusted to a suitable flow rate and pressure to ensure both effective cooling and long-term safe and stable operation. The coolant 4 should meet the following characteristics: high thermal conductivity, high specific heat capacity, low viscosity, wide operating temperature range, chemically stable, low absorption of pump light, and no chemical reaction with the thin rod-shaped laser working medium 3 and the glass sleeve 5. The thin rod-shaped laser working medium 3 is relatively thin (approximately 1 mm in diameter) and has a large length-to-diameter ratio (effective pump length approximately 50-110 mm). Furthermore, the fracture stress limit of this type of material is typically low. Therefore, careful installation is essential. It is crucial to ensure accurate installation and fixing, maintain the sealing performance of the coolant flow channels, and prevent breakage under stress. Minimize installation stress; if necessary, specialized tooling can be fabricated to assist in installation and debugging.

[0027] Among them, the total mirror 7 and output mirror 8 of the laser resonator should be selected with appropriate cavity shape and reflectivity based on theoretical calculations and experimental verification of laser dynamics.

[0028] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity, characterized in that, include: LD bar (1), composite reflective focusing cavity (2), and thin rod laser working medium (3); LD bar (1) and thin rod laser working medium (3) are arranged in the composite reflective focusing cavity (2). The pump light emitted from the emitting point of LD bar (1) is reflected by the elliptical inner wall of the upper half of the composite reflective focusing cavity (2) and then converges at the axial position of the thin rod laser working medium (3). The residual pump light after being absorbed by the thin rod laser working medium (3) reaches the semi-circular inner wall of the lower right half of the composite reflective focusing cavity (2) and is reflected back to the thin rod laser working medium (3) along the original path, so that the residual pump light energy is absorbed again, and efficient pumping is achieved.

2. The semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity as described in claim 1, characterized in that, The inner wall of the composite reflective focusing cavity (2) is divided into three regions according to different functions and structures. Region 1: The upper half of the inner wall of the cavity is semi-elliptical in shape. The left and right foci of the ellipse are the light emission point of the LD bar (1) and the axis of the thin rod-shaped laser working medium (3), respectively. Region 2: The lower right half of the inner wall of the cavity is semi-circular in shape. Its center coincides with the right focus of the ellipse, which is the axis of the thin rod-shaped laser working medium (3). The diameter of the semi-circle is the difference between the major axis of the ellipse and the focal length. Region 3: The lower left half of the inner wall of the cavity is irregular in shape. Its inner wall has no reflective function and has no requirements for surface shape and reflectivity. It plays a structural support role for the LD bar (1) and a role in sealing the cavity.

3. The semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity as described in claim 2, characterized in that, LD bar (1) is a linear array semiconductor laser diode rake bar that provides a pump source for the laser module. The fast axis divergence angle is parallel to the XY plane. Among them, the X direction is the direction perpendicular to the YZ plane, the Y direction is the direction of the major axis of the ellipse, and the Z direction is the direction parallel to the central axis of the thin rod-shaped laser working medium (3).

4. The semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity as described in claim 3, characterized in that, The side surface of the thin rod-shaped laser working medium (3) is roughened into a semi-transparent surface. In addition to absorption, reflection and transmission of pump light, it also has some diffuse reflection and diffuse transmission.

5. The semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity as described in claim 4, characterized in that, The outer part of the thin rod-shaped laser working medium (3) is a glass sleeve (5) with the same center as it. The gap between the two is filled with flowing coolant (4) to cool the thin rod-shaped laser working medium (3).

6. The semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity as described in claim 5, characterized in that, The inner and outer surfaces of the glass sleeve (5) are coated with an anti-reflection film that is sensitive to the pump light wavelength.

7. The semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity as described in claim 6, characterized in that, The glass sleeve (5) is provided with coolant inlet and outlet (6) at both ends, and the coolant inlet and outlet (6) are connected to the external water-cooled equipment.

8. The semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity as described in claim 7, characterized in that, Outside the composite reflective focusing cavity (2), a total reflection mirror (7) and an output mirror (8) are coaxially arranged at both ends of a thin rod-shaped laser working medium (3).

9. The semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity as described in claim 8, characterized in that, The position of the emitting point of LD bar (1) is misaligned with the left focal point of region 1 of the composite reflective focusing cavity (2), and the misalignment distance is equal to the width of the emitting slit of LD bar (1), which is 0.1 mm.

10. The semiconductor side-pumped solid-state laser module based on a composite reflective focusing cavity as described in claim 9, characterized in that, The slit width of the LD bar (1) is an order of magnitude smaller than the diameter of the thin rod-shaped laser working medium (3).

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