Pumping module of vcsel side-pumped solid-state laser and corresponding solid-state laser

Abstract

A pumping module of a VCSEL side-pumped solid-state laser and a corresponding solid-state laser. The pumping module uses a design of pumping in an even number of directions, achieves a symmetrical pumping cavity and a mutual reflection chamber, and improves pumping light distribution uniformity. By means of the high reflectivity characteristic of surfaces of VCSEL chips (2) and a packaging substrate and a heat sink (1) therefor, a design in which no independent reflection chamber is provided and the heat sink (1) is integrated is realized, the structure is simplified, and the symmetry of light spots is improved. In addition, a cooling pipe (4) having a frosted outer surface is introduced, so that the uniformity of light beams is further improved by means of a diffusion mechanism, and reflection on the surfaces of the VCSEL chips (2) is used to compensate for possible loss, thereby ensuring that optical-to-optical efficiency is almost unchanged. By using an eccentric pumping structure and an optimized wavelength distribution of the VCSEL chips (2), the absorption uniformity of a crystal rod (200) is further improved; and the uniformity of light beams can be effectively improved, especially when the diameter of the crystal rod (200) is large. The present invention has the advantages of a simple structure, stable performance and good light spot symmetry.

Description

Pumping module of VCSEL side-pumped solid-state laser and corresponding solid-state laser Technical Field

[0001] The present invention relates to a pump module of a VCSEL side-pumped solid-state laser and also to a solid-state laser comprising the pump module, belonging to the technical field of solid-state lasers. Background Art

[0002] Compared with traditional lamp-pumped solid-state lasers, side-pumped solid-state lasers using laser diode bars have the advantages of compact structure, high luminous efficiency, and stable performance. However, in high-power all-solid-state lasers, the pump module usually adopts side multi-directional pumping technology. This design requires the crystal rod and pump source to be cooled separately, resulting in a complex heat dissipation structure and difficulty in miniaturization. Therefore, it is not suitable for compact high-power all-solid-state lasers. In addition, the existing pump cavity design usually uses an independent reflector cavity component. In order to avoid internal amplification and damage of the edge-emitting semiconductor laser chip caused by the opposite reflection of the pump light, an odd-numbered direction pumping design is usually adopted, such as three-way, five-way, seven-way, etc. In order to improve the utilization rate of the pump light, a slit reflector cavity is used in the design to reflect and utilize the pump light that passes through the laser crystal once but is not absorbed. The structure of this superposition of the pump source and the reflector cavity is complex, the reflection efficiency is low, and it is difficult to reduce the radial size. Summary of the Invention

[0003] The primary technical problem to be solved by the present invention is to provide a pump module for a VCSEL side-pumped solid-state laser.

[0004] Another technical problem to be solved by the present invention is to provide a solid-state laser including the pump module.

[0005] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0006] According to a first aspect of an embodiment of the present invention, a pump module for a VCSEL side-pumped solid-state laser is provided, comprising a pump cavity and a crystal rod; the crystal rod is a working rod of the solid-state laser, and the pump cavity is arranged around the crystal rod;

[0007] The pump cavity includes a heat sink and a pump chip; wherein the heat sink is a hollow cylinder, and the inner surface of the heat sink is provided with a mounting surface; the mounting surface is a plane parallel to the axis of the heat sink; in a cross section perpendicular to the axis of the crystal rod, the projections of the multiple mounting surfaces form a regular polygon; the mounting surfaces are an even number, including multiple groups of mounting surfaces and corresponding mounting surfaces, and the mounting surfaces and the corresponding mounting surfaces are arranged in a facing direction;

[0008] The pump chip is a VCSEL chip, which is arranged on the mounting surface; the light emitting direction of the pump chip located on the mounting surface and the light emitting direction of the pump chip located on the corresponding mounting surface are aligned in a positive direction with each other.

[0009] According to a second aspect of an embodiment of the present invention, there is provided another pump module for a VCSEL side-pumped solid-state laser, comprising a pump cavity and a crystal rod, wherein the crystal rod is a working rod of the solid-state laser, and the pump cavity is disposed around the crystal rod;

[0010] The pump cavity includes a heat sink and a pump chip; wherein the heat sink is a hollow cylinder, and the inner surface of the heat sink is provided with a mounting surface; the mounting surface is a plane parallel to the axis of the heat sink; in a cross section perpendicular to the axis of the crystal rod, the projections of the multiple mounting surfaces form a regular polygon; the mounting surfaces are an even number, including multiple groups of mounting surfaces and corresponding mounting surfaces, and the normal directions of the mounting surfaces and the corresponding mounting surfaces are offset;

[0011] The pump chip is a VCSEL chip, which is arranged on the mounting surface;

[0012] In a cross section perpendicular to the axis, the light emission direction of the pump chip located on the mounting surface, the diameter passing through the center of the pump chip and the axis of the crystal rod are offset from each other by a predetermined angle α. The predetermined angle α is such that the distance between the chip center normals of the two pump chips on the mounting surface and the corresponding mounting surface is less than the diameter of the crystal rod.

[0013] Preferably, the pump chip is a VCSEL chip with a top-emitting structure.

[0014] Preferably, the pump module further includes a cooling pipe;

[0015] The axis of the cooling tube coincides with the axis of the crystal rod, is used to surround the crystal rod, and allows cooling gas or liquid to pass through to cool the crystal rod, and is made of a highly light-transmitting material.

[0016] Preferably, the cooling tube has a polished outer surface or a frosted outer surface, and the roughness of the frosted outer surface is Ra0.1 to Ra80 μm.

[0017] Preferably, the cooling tube has a polished outer surface or a frosted outer surface, and the roughness of the frosted outer surface is Ra0.2 to Ra50 μm.

[0018] Preferably, along the axis of the crystal rod, on multiple cross sections perpendicular to the axis, a center wavelength difference M between a group of pump chips located at the same cross section and an average center wavelength difference N between different groups of pump chips located at different cross sections satisfy M<N.

[0019] Preferably, along the axis of the crystal rod, on multiple cross sections perpendicular to the axis, a center wavelength difference M between a group of pump chips located at the same cross section and an average center wavelength difference N between different groups of pump chips located at different cross sections satisfy M<N.

[0020] According to a third aspect of an embodiment of the present invention, a solid-state laser is provided, comprising the aforementioned pump module, an output mirror, and a reflector; wherein,

[0021] The reflector and the output mirror are located on opposite sides of the pump module, and a resonant cavity is formed between the reflector and the output mirror.

[0022] The output mirror is arranged in the light output direction of the resonant cavity and is used for outputting light.

[0023] Compared with the prior art, the pump module of the VCSEL side-pumped solid-state laser and the corresponding solid-state laser provided by the present invention have the following technical effects: First, the pump module adopts an even-numbered direction pumping design to achieve a symmetrical pump cavity and mutual reflection chamber, thereby improving the uniformity of the pump light distribution. Secondly, by utilizing the high reflective properties of the VCSEL chip and its packaging substrate and heat sink surface, a design without an independent reflection cavity and an integrated heat sink is realized, avoiding the loss of pump light by the traditional reflection cavity component, simplifying the structure and improving the symmetry of the light spot. In addition, by introducing a cooling tube with a frosted outer surface, a diffusion mechanism is introduced to further improve the uniformity of the light beam, and at the same time, the surface reflection of the VCSEL chip is used to compensate for the loss that may be caused by the frosted surface, ensuring that the light efficiency remains almost unchanged. Finally, the eccentric pumping structure and the optimized wavelength distribution of the VCSEL chip are adopted to further improve the absorption uniformity of the crystal rod, especially when the crystal rod diameter is large, which can effectively improve the uniformity of the light beam. In summary, the pump module and solid-state laser provided by the present invention have significant advantages in terms of simple structure, stable performance, good spot symmetry, etc., and are particularly suitable for application in high-power all-solid-state lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG1A is a cross-sectional schematic diagram of a pump module of a VCSEL side-pumped solid-state laser in a first embodiment of the present invention;

[0025] FIG1B is a schematic cross-sectional view along the AA direction in FIG1A with the crystal rod removed;

[0026] FIG1C is a schematic cross-sectional view along the AA direction in FIG1A with a crystal rod;

[0027] FIG2 is a cross-sectional diagram showing the distribution of pump power absorbed by a laser crystal rod when the same cross-section is irradiated by five pump light sources in the prior art;

[0028] 3 is a cross-sectional view showing the distribution of absorbed pump power when the same cross-section of a laser crystal rod is irradiated by six pump light sources in an embodiment of the present invention;

[0029] 4 is a schematic cross-sectional view of a pump module of a VCSEL side-pumped solid-state laser in a second embodiment of the present invention;

[0030] FIG5 is a schematic structural diagram of a solid-state laser including the pump module in a third embodiment of the present invention;

[0031] 6 is a schematic cross-sectional view of a pump module of a VCSEL side-pumped solid-state laser in a fourth embodiment of the present invention;

[0032] FIG7 is a diagram showing the light intensity distribution of the pump module of the VCSEL side-pumped solid-state laser in FIG4 and FIG6 , in a cross section perpendicular to the crystal rod;

[0033] 8 is a schematic diagram showing a cross-sectional structure of a pump module of a VCSEL side-pumped solid-state laser in a fifth embodiment of the present invention, and a comparison with the cross-sectional structure of a pump module of a VCSEL side-pumped solid-state laser in a fourth embodiment;

[0034] FIG9 is a schematic diagram comparing the light intensity distribution of a pump module of a VCSEL side-pumped solid-state laser in a fifth embodiment of the present invention and a pump module of a VCSEL side-pumped solid-state laser in a fourth embodiment, in a cross section perpendicular to the crystal rod;

[0035] FIG10 is a schematic structural diagram of a crystal rod and a pump chip in a pump module of a VCSEL side-pumped solid-state laser in a sixth embodiment of the present invention. DETAILED DESCRIPTION

[0036] The technical content of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] The technical concept in the embodiments of the present invention is to use a vertical-cavity surface-emitting semiconductor laser (VCSEL) as the pump light source for the laser crystal rod, while simultaneously forming a pump cavity with a VCSEL chip. Because the electrodes on the VCSEL chip surface are made of gold, as is the packaging substrate, the surface DBR has a reflectivity of 98% or even over 99%. Therefore, the VCSEL chip surface has an extremely high reflectivity for the light beam, serving both as a pump source to emit the light beam and as a reflective surface, causing the light beam to reflect multiple times within the pump cavity to form a laser. Furthermore, because the VCSEL chip is used and a closed reflective cavity (without gaps) is formed around the crystal rod (working rod), the light beam serving as the pump source is emitted from the surface of the VCSEL chip facing the crystal rod, passes through the crystal rod, and strikes the VCSEL chip located directly opposite it, where it is then reflected multiple times. This eliminates the need for gaps in the reflective cavity to allow the pump light to enter, as is required in the prior art, thereby improving the utilization of the pump light. Furthermore, with an even number of VCSEL chips facing each other and symmetrically arranged, the light beam can be emitted completely symmetrically to the opposite VCSECL chip and then reflected multiple times, which can improve the uniformity of the light spot.

[0038] First embodiment

[0039] The first embodiment of the present invention provides a pump module for a VCSEL side-pumped solid-state laser, comprising a pump cavity 100 and a crystal rod 200 , which are coaxially arranged. The pump cavity 100 is arranged around the crystal rod 200 .

[0040] The pump cavity 100 includes a heat sink 1 and a pump chip 2. The pump chip 2 is a VCSEL chip. Although a bottom-emitting VCSEL chip can be used, it is preferably a top-emitting VCSEL chip.

[0041] FIG1A shows a schematic cross-sectional view perpendicular to the axial direction of the pump cavity 100 provided in this embodiment. The heat sink 1 is a hollow cylinder with an inner cavity, formed integrally from a highly thermally conductive, easily machined material (e.g., silicon carbide, aluminum nitride, etc.). The heat sink 1 is used to mount and dissipate heat for the pump chip 2. Preferably, the heat sink 1 is constructed from multiple components, such as two, three, or four components. This embodiment illustrates a heat sink 1 constructed from two components.

[0042] The heat sink 1 includes a first component 11 and a second component 12. The interface between the first and second components 11, 12 is parallel to the axis of the heat sink 1 (coaxial with the crystal rod), forming a hollow cylinder. The inner surface of the heat sink 1, as projected onto a cross section, is a regular polygon. The inner surface of the heat sink 1 includes multiple mounting surfaces 1a, which are planes parallel to the axis of the crystal rod 200. The mounting surfaces 1a are arranged in a circular array, centered on the cross-sectional projection of the axis of the heat sink 1.

[0043] As shown in Figure 1B, the first component 11, on a cross section perpendicular to the axis of the heat sink 1, includes a first mounting surface 1a1, a second mounting surface 1a2, and a third mounting surface 1a3. The first mounting surface 1a1 connects to one side of the second mounting surface 1a2, with the two surfaces forming a certain angle. The other side of the second mounting surface 1a2 connects to the third mounting surface 1a3, with the two surfaces forming a certain angle. The structure of the second component 12 is identical to that of the first component 11. Therefore, in the heat sink 1 formed by combining the first component 11 and the second component 12, the projection of the mounting surface 1a on the cross section perpendicular to the axis of the heat sink 1 forms a regular hexagon. In other words, the mounting surfaces are an even number, including multiple sets of corresponding mounting surfaces (the first mounting surface 1a1 on the first component 11 and the corresponding mounting surface 1a1' on the second component 12), and the mounting surfaces and their corresponding mounting surfaces are arranged in a facing direction (i.e., aligned in a positive direction with each other). The so-called facing direction means that the two are symmetrical about a plane containing the axis of the heat sink 1. In other words, directly opposite means that the two corresponding mounting surfaces are in a plane-symmetrical relationship based on the plane where the axis of the crystal rod 200 is located.

[0044] In this embodiment, since the heat sink 1 is a two-piece assembly, each heat sink 1 has two or more mounting surfaces 1a for mounting a corresponding number of pump chips 2. Each mounting surface 1a has the same shape and size, so that after assembly, the mounting surfaces 1a are symmetrically arranged and face each other.

[0045] The back side of the heat sink 1, that is, the side opposite to the mounting surface, is designed to have a circular or rectangular shape after assembly, so that each pump chip can dissipate heat evenly. It should be noted that multiple pump chips located on the same cross section share one heat sink.

[0046] The heat sink 1 and the pump chip 2 surround and form an inner cavity 3. The inner cavity 3 surrounds the crystal rod 200 and is used to form a cooling air path or a cooling flow channel.

[0047] In this embodiment, the heat sink 1 is constructed from two pieces, enclosing the inner cavity 3. Furthermore, the pump chips 2 are located on the mounting surface 1a of the heat sink 1. Consequently, multiple pump chips 2 on the same cross-section are connected to form a closed chip ring. Overall, the crystal rod 200 is surrounded by multiple chip rings. There are no gaps between the multiple pump chips 2 (chip rings) on the same cross-section for the light beam to enter the crystal rod 200.

[0048] Therefore, on the cross section perpendicular to the axis of the pump cavity 100, the number of pump chips 2 arranged in a polygonal shape is n, and n≥4. Preferably, n is an even number greater than or equal to 6. This embodiment is illustrated by n=6. As shown in Figure 1C, the pump chip 2 is arranged on the mounting surface 1a, and the light-emitting surface of the pump chip 2 is in the opposite direction to the mounting surface 1a. Therefore, the direction of the emitted light of the pump chip 2 located on the mounting surface is perpendicular to the axis of the crystal rod 200 and points to the pump chip 2 located on the corresponding mounting surface. Since the mounting surfaces are arranged face to face, the two pump chips 2 located on the corresponding mounting surfaces are also arranged face to face. The pump chips 2 arranged face to face have the same performance parameters, and their emitted light beams are completely symmetrical and reflected, thereby improving the pumping efficiency.

[0049] Figure 2 shows the energy distribution when n is an odd number, 5 (hereinafter referred to as five-way pumping, a prior art technique); Figure 3 shows the energy distribution when n is an even number. A comparison shows that when an odd number of pump chips 2 are present on the same cross-section, they are not fully reflective of each other, whereas when an even number of pump chips are present, they are fully reflective (transmissive). Therefore, six-way pumping exhibits greater symmetry and more uniform energy distribution than five-way pumping.

[0050] Because the number of pump chips 2 provided in this embodiment is n=6, the six mounting surfaces 1a are connected end to end and arranged in a hexagonal pattern centered on the axis of the heat sink 1. Furthermore, because the surface reflectivity of the pump chips 2 exceeds 99%, and the surface electrodes are gold layers, and the packaging substrate material is also gold layers, the pump chips 2 surround a hexagonal laser reflection cavity, which has excellent reflection effects. Therefore, the pump cavity 100 proposed in this embodiment of the present invention does not require the provision of an independent reflection cavity assembly and a light-transmitting window-type reflection cavity assembly. The pump chip 2 and the heat sink 1 can form a reflection cavity, thus avoiding the loss of pump light caused by the independent reflection cavity assembly. In addition, due to the mutual reflection between the chips of an even number of pump chips, the overall energy distribution is more uniform.

[0051] Second embodiment

[0052] This embodiment is based on the first embodiment, but differs from the first embodiment in that the pump cavity 100 provided in this embodiment further includes a cooling tube (also called a glass flow tube) 4, and the heat sink 1 further includes cooling holes 13. Multiple cooling holes 13 are provided in the heat sink 1, extending along the axis of the heat sink 1 (which is also the axis of the crystal rod 200).

[0053] As shown in FIG. 4 , the cooling hole 13 is located between the mounting surface 1 a and the outer surface of the heat sink 1 , and is used to form a cooling air path or a cooling flow channel for the coolant to provide heat dissipation and cooling for the heat sink 1 .

[0054] Cooling tube 4 is located in inner cavity 3 and extends along the axis of crystal rod 200. The axis of cooling tube 4 coincides with the axis of heat sink 1, and is used to surround crystal rod 200, forming a cooling flow channel for cooling medium 300, which is used to provide heat dissipation and cooling for crystal rod 200. Preferably, cooling tube 4 is a structure integrally formed of a highly transparent material such as optical glass or quartz, with a conventional polished outer surface (for example, a surface roughness of less than Ra 0.2μm, or less than Ra 0.1μm).

[0055] To verify the technical effects of the present invention, an experimental verification is conducted using the second embodiment. Taking the six-way pumped Nd:YAG module of the present invention as an example, an Nd:YAG crystal is used as the crystal rod 200. The Nd:YAG crystal has a diameter of 5mm, a length of 90mm, and an Nd doping concentration of 1%. Forty-eight 808nm VCSEL chips are used as the pump chip 2. The VCSEL chips are divided into eight circles (six VCSEL chips per circle) surrounding the crystal rod 200. The test conditions are as follows: ① The VCSEL chip has an operating power of 120W and an operating time of 1ms; ② A 250mm flat resonant cavity is used; ③ The output mirror transmittance T = 20%; and ④ The cooling water temperature is 25°C. A 1064nm laser output with a single pulse energy of 2.2J (1ms, 10Hz) is obtained. The optical efficiency = 2.2 / (120×48×0.001) = 38.2%. The light-to-light conversion efficiency of the pump module is basically the same as that of the pump module with a reflective cavity.

[0056] Third embodiment

[0057] This embodiment provides a solid-state laser including the above-mentioned pump module. As shown in FIG5 , the solid-state laser includes an output mirror 300, a pump module (which includes a pump cavity 100 and a crystal rod 200), a reflector 400, and may further include a control module 500 and a cooling module 600.

[0058] The output mirror 300, pump module, and reflector 400 are coaxially arranged in sequence, with the pump cavity 100 surrounding the crystal rod 200. The reflector 400 and output mirror 300 are located on opposite sides of the pump module, forming a resonant cavity between them. In other words, the pump cavity 100 surrounds the crystal rod 200, while the reflector 400 is positioned opposite the light-emitting direction of the crystal rod 200 and coaxial with the crystal rod 200. The reflective surface of the reflector 400 is perpendicular to the axis of the crystal rod 200. The output mirror 300 is positioned in the light-emitting direction of the crystal rod 200 and coaxial with the crystal rod 200.

[0059] The reverse light from the crystal rod 200 reaches the reflector 400 and is reflected back to the crystal rod 200, and is emitted from the forward direction of the crystal rod 200. The forward light from the crystal rod 200 reaches the output mirror 300 and is emitted through the output mirror 300.

[0060] The cooling module 600 is connected to the cooling air path or the cooling liquid cooling channel of the pumping chamber 100 , inputs cooling air or cooling liquid into the pumping chamber 100 , and receives the cooling air or cooling liquid heated by the pumping chamber 100 .

[0061] The control module 500 is connected to the pump cavity 100 and the cooling module 600, receives parameters such as the energy of the emitted laser and the temperature of the pump cavity 100, and controls parameters such as the input current, voltage and cooling medium flow of the pump cavity 100 based on these parameters, so that the pump module can stably output laser.

[0062] In experimental verification of the second embodiment, the transmittance T of output mirror 300 was 20%, and the resonant cavity formed by reflector 400 and output mirror 300 was 250 mm long. The cooling water temperature of cooling module 600 was 25°C, achieving a single-pulse energy of 2.2 J (1 ms, 10 Hz) at 1064 nm.

[0063] Fourth embodiment

[0064] Unlike the cooling tube 4 in the second embodiment, whose inner and outer surfaces are polished (to make them smooth surfaces with a roughness of Ra0.1μm and below), the cooling tube 4a in this embodiment is a tubular structure with a frosted outer surface and a smooth inner surface. The remaining structures in this embodiment are the same as those in the second embodiment, so they are not repeated here. The roughness of the outer surface 4a1 of the cooling tube 4a is Ra0.1μm to Ra80μm, preferably Ra0.2μm to Ra50μm, Ra0.5μm to Ra35μm, Ra1μm to Ra25μm, or Ra1μm to Ra15μm. For example, the outer surface 4a1 of the cooling tube 4a is obtained by grinding with abrasives such as corundum, silicon carbide, boron carbide, etc. with a mesh size of 50 to 240 (preferably 60 to 200 or 100-140 mesh).

[0065] As we all know, pump light is typically 808nm, and the greatest impact on optical efficiency is the loss at the interface between air and glass. Typically, the outer surface of the cooling tube (the interface between air and glass) experiences a loss of approximately 4%. The inner surface of the cooling tube (the interface between water and glass) also experiences a loss, slightly less than the outer surface. The interface loss between air and glass generally increases with increasing glass surface roughness (from polished to frosted). This is why cooling tubes used for water cooling of crystal rods typically have a polished outer surface.

[0066] To this end, in one embodiment of the present invention, the reflective function of the surface of the VCSEL chip ring is utilized to reduce losses. As shown in Figure 6, the frosted surface of the cooling tube 4 diffuses the pump beam, providing diffuse transmission and reflection for the pump beam. Diffuse transmission significantly improves the uniformity of the pump beam's absorption by the crystal rod during the first transmission. On the one hand, because most of the pump energy is absorbed when the beam emitted by the VCSEL chip passes through the crystal rod for the first time; on the other hand, because the diffusely transmitted and reflected beam will be reflected again by the surface of the VCSEL chip (for example, a metal layer such as copper or gold formed by vapor deposition) and re-enter the crystal rod, the additional loss caused by the frosted surface compared to the polished surface can be ignored and has almost no impact on the pump efficiency (optical efficiency). Therefore, the cooling tube 4 with a frosted surface can improve the symmetry and uniformity of the laser light without reducing (or almost reducing) the optical efficiency.

[0067] Figure 7 provides the light intensity distribution of the output end face of an Nd:YAG laser with a polished outer surface and a frosted outer surface cooling tube, demonstrating that the optical efficiency of the pump module provided by this embodiment is the same or substantially the same as that of a conventional design, while also improving uniformity and symmetry. Figure 7 shows that the optical efficiency of a 5mm diameter Nd:YAG laser using a polished outer surface cooling tube is 39%. The optical efficiency of a 5mm diameter Nd:YAG laser using a frosted outer surface cooling tube is 38%. The optical efficiency of a 6mm diameter Nd:YAG laser using a polished outer surface cooling tube is 44%. The optical efficiency of a 6mm diameter Nd:YAG laser using a frosted outer surface cooling tube is 45%. This shows that the light output efficiency of Nd:YAG lasers with different diameters, whether the cooling tube has a polished outer surface or a frosted outer surface, is almost the same.

[0068] Furthermore, Figure 7 shows that when the cooling tube 4 has a frosted outer surface, the high-temperature area at the center of the crystal rod 200 accounts for a larger proportion, and the distribution of the high-temperature area is more uniform. It was also observed that the brightness of the Nd:YAG crystal rod surface with the frosted outer surface of the cooling tube decreased. Since no significant difference in light efficiency was observed from light to light, this optical adjustment measure, replacing the polished outer surface of the cooling tube 4 with a frosted outer surface, did not result in any loss of light efficiency.

[0069] The experimental conditions for the above experimental verification are as follows: in the six-way pumped Nd:YAG module shown in Figure 6, an Nd:YAG crystal with a doping concentration of 0.8% was used as the crystal rod, with diameters of 5 mm and 6 mm, respectively, and a length of 90 mm. Forty-eight 808nm VCSEL chips were used as pump chips, arranged in eight circles (six VCSEL chips per circle) surrounding the crystal rod 200. The distance from the crystal plane of the pump chip to the center of the Nd:YAG crystal rod 200 was 9.5 mm. The central wavelength of all VCSEL pump chips had a deviation of ±0.5 nm. The outer diameter of the cooling tube was 10 mm and the inner diameter was 8 mm in both the polished and frosted conditions. The frosted surface was produced using 120-mesh corundum.

[0070] Fifth embodiment

[0071] Unlike the first embodiment, the light emission direction of the VCSEL chip in this embodiment is not toward the pump chip located on the corresponding mounting surface, but deviates from the predetermined angle. This structure is referred to as "encentric pumping". FIG8 compares the difference in the light emission direction of the VCSEL chips in the third and fourth embodiments. As shown in the figure, on a cross section perpendicular to the crystal rod, the light emission direction of the symmetry center of the VCSEL chip in the third embodiment passes through the axis of the crystal rod 200 (referred to as "centric pumping"). The light emission direction of the symmetry center of the VCSEL chip in the fourth embodiment does not pass through the axis of the crystal rod 200. The light emission directions of the symmetry centers of all VCSEL chips form a radially symmetrical structure around the axis.

[0072] Specifically, as shown in Figure 8, the pump module of the VCSEL side-pumped solid-state laser in this embodiment includes a pump cavity 3 and a crystal rod 200. The crystal rod 200 is the working rod of the solid-state laser. The pump cavity 3 is arranged around the crystal rod 200; the pump cavity 3 includes a heat sink 1 and a pump chip 2 (a top-emitting VCSEL chip). The heat sink 1 is a hollow cylinder with a mounting surface 1a provided on its inner surface. The mounting surface 1a1 is a plane parallel to the axis of the heat sink 1. In a cross section perpendicular to the axis of the crystal rod 200, the projections of the multiple mounting surfaces 1a form a regular polygon. Moreover, in a cross section perpendicular to the axis, the mounting surfaces are an even number, including multiple groups of mounting surfaces and corresponding mounting surfaces. The normal directions of the mounting surfaces and corresponding mounting surfaces are parallel to each other and perpendicular to the axis of the crystal rod. The pump chip is a VCSEL chip, which is arranged on the mounting surface. In a cross section perpendicular to the axis, the light emission direction of the pump chip located on the mounting surface deviates from the diameter passing through the center of the pump chip and the axis of the crystal rod by a predetermined angle α (the predetermined angle α is such that the distance between the normals passing through the chip centers of the two pump chips on the mounting surface and the corresponding mounting surface is less than the diameter of the crystal rod). In other words, the mounting surface 1a is rotated around its own central axis parallel to the axis of the heat sink 1 by a set angle α. For example, the mounting surface 1a is rotated 8° clockwise around its central axis. Therefore, the light emission direction of the pump chip 2 changes from a centripetal arrangement pointing toward the axis of the crystal rod 200 (the third embodiment) to an eccentric arrangement pointing to one side of the axis of the crystal rod 200 (the fourth embodiment). That is, the centripetal pumping structure is changed to an eccentric pumping structure. The technical details not described in this embodiment are the same as those in the first embodiment and are not repeated here.

[0073] As shown in Figure 9, this eccentric pumping structure further improves uniformity. For the pump module with a 6nm diameter crystal rod and frosted cooling tube used in the experiment shown in Figure 7, the optical efficiency was 45% when the pump module used a centrifugal pumping structure, and 39% when the pump module used an eccentric pumping structure.

[0074] However, the concentration of the high-temperature zone at the center of the crystal rod in the eccentric pumping structure is reduced, and the absorption at the edge of the Nd:YAG crystal rod is enhanced. This is because, in the eccentric pumping structure, the multiple pump beams are not directly irradiated on the axis of the crystal rod, but on the edge of the crystal rod, forming a ring around the axis. This changes the distribution of the laser beam, enhancing the absorption at the edge of the crystal rod, resulting in a distribution with increased edge intensity and decreased center intensity. Conventional technologies have difficulty improving uniformity, especially when the diameter of the crystal rod (for example, a diameter greater than or equal to 8mm) is much larger than the pump beam path length. However, the use of an eccentric pumping structure can change the beam profile from a Gaussian-like distribution to a distribution close to a flat top, improving uniformity. Therefore, when the crystal rod diameter is large, an eccentric pumping structure is preferred to improve uniformity.

[0075] Although this embodiment compares the pump structure of a cooling tube with a frosted surface, the eccentric pump structure can still improve uniformity for a cooling tube with a polished surface, such as in the first embodiment. This will not be discussed in detail here. In other words, the pump structures of the first to fourth embodiments can all utilize an eccentric pump structure to further improve uniformity.

[0076] Sixth embodiment

[0077] As shown in FIG10 , based on any of the first through fifth embodiments, this embodiment further optimizes the design of the pump module: In any of the aforementioned pump modules, along the axial direction of the crystal rod, in a group of pump chips (VCSEL chips) arranged in a ring on each cross-section perpendicular to the axial direction, the center wavelengths of the light-emitting diodes of each pump chip are made close (for example, the center wavelength difference is less than 1 nm, or even 0.5 nm). In other words, while the center wavelength difference between each group of pump modules in the first through fifth embodiments is not restricted, the center wavelength difference between each group of pump modules in this embodiment is minimized, and the center wavelength difference between different groups can be the same or different.

[0078] Specifically, in the pump module of the VCSEL side-pumped solid-state laser in this embodiment, multiple groups of pump chips are arranged along the axial direction of the crystal rod. All laser diodes in each pump chip operate at a single wavelength. On a plane perpendicular to the axial direction and passing through the center, the projection of each group of pump chips is centered on the axis of the crystal rod and arranged in a radially symmetrical ring shape. All laser diodes in this group of pump chips (VCSEL chips) have the same or similar optical power and spectral characteristics. Because the crystal rod has different absorption levels for different wavelengths, the pumping efficiency of the Nd:YAG crystal rod is very sensitive to the wavelength distribution of the laser diodes. To achieve effective absorption of light by the Nd:YAG crystal rod (improve the absorptivity), the laser diodes are typically designed with a central wavelength of 804nm to 809nm to match the absorption peak of the Nd:YAG crystal rod. However, wavelength deviations between the laser diodes in the cross-section and axial directions of the Nd:YAG crystal rod can lead to a decrease in the uniformity of the light emitted by the Nd:YAG crystal rod. The laser diode's central wavelength must be matched to the diameter and doping level of the Nd:YAG crystal rod to pre-design the appropriate pump beam path length. For larger diameters or higher doping levels, a pump wavelength with lower absorption is desirable (shifting the pump wavelength away from the absorption peak). For smaller diameters or lower doping levels, it's preferable to keep the pump wavelength as close to the absorption peak as possible. Ideally, all pump chips should have the same or nearly the same wavelength (e.g., center wavelengths with a difference of less than 1 nm, or even less than 0.5 nm).

[0079] However, if the optimal wavelength cannot be achieved for various reasons, another feasible alternative is: in each group of pump chips in the cross section perpendicular to the axial direction of the crystal rod, each pump chip has the same or nearly the same central wavelength (for example, the central wavelength difference is less than 1nm, or even less than or equal to 0.5nm); and the wavelength difference between different groups of pump chips is greater than 1nm (but the path length of the pump beam must also be considered, so it cannot be too large, for example, no more than 5nm, and preferably no more than 3nm). In other words, the central wavelength difference M of the pump chips in the same group and the average central wavelength difference N of the pump chips in different groups satisfy M<N. The central wavelength difference M of the pump chips in the same group refers to the difference between the wavelengths of the pump chip with the largest wavelength and the pump chip with the smallest wavelength in the same group. The average central wavelength difference N of the pump chips in different groups refers to the difference between the average wavelength of the pump chips in the first group and the average wavelength of the pump chips in the second group. The first group of pump chips and the second group of pump chips are respectively located at different cross sections perpendicular to the axial direction of the crystal rod.

[0080] For example, at current industrial standards, the center wavelength error of semiconductor laser chips is typically controlled within ±3nm. Therefore, to improve chip utilization (from an economic perspective), the center wavelength error of VCSEL chips within the same group (the same circle in Figure 10) can be required to be within ±0.5nm (M = 0.5nm), and the wavelength difference between different groups can be within ±3nm (N = 3nm). At the same time, the center wavelength of all VCSEL chips must be within the high-efficiency absorption range of the crystal rod (for Nd:YAG crystal rods, the center wavelength of all VCSEL chips is required to be between 803-809nm). For example, in the figure, the wavelength of the first group of VCSEL chips is 807.2nm, the wavelength of the second group of VCSEL chips is 804.6nm, the wavelength of the third group of VCSEL chips is 807.2nm, and the wavelength of the fourth group of VCSEL chips is 808.3nm. In this case, the optical power control of the laser diode follows the same rules. Because the wavelengths of each group of pump chips are close, the uniformity of the light output of the solid-state laser is improved.

[0081] In summary, the pump module of the VCSEL side-pumped solid-state laser and the corresponding solid-state laser provided in the embodiment of the present invention introduce an even pump direction, realize a symmetrical pump cavity and a mutual reflection chamber, and thus improve the uniformity of the pump distribution. Moreover, by utilizing the high reflective properties of the VCSEL chip and / or the packaging substrate and the heat sink surface, a pump module without an independent reflection cavity, an integrated heat sink, and pump light that can be reflected is realized, thereby avoiding the loss of pump light by the independent reflection cavity component, and having the characteristics of simple structure and good light spot symmetry. The solid-state laser provided in the embodiment of the present invention utilizes a reflector and an output mirror to realize the output of the solid-state laser, cools the temperature through a cooling module, and controls the input and output capabilities of the solid-state laser through a control module.

[0082] Furthermore, the pump module of the VCSEL side-pumped solid-state laser and the corresponding solid-state laser provided in the embodiments of the present invention utilize a cooling tube with a frosted outer surface to introduce a diffusion mechanism to improve uniformity; the surface reflection of the VCSEL chip is also utilized to compensate for the loss caused by the frosted outer surface, thereby achieving almost unchanged optical efficiency of the pump module (compared to a pump module with the same structure but a cooling tube with a polished surface).

[0083] Furthermore, the pump module of the VCSEL side-pumped solid-state laser and the corresponding solid-state laser provided in the embodiments of the present invention utilize an eccentric pumping structure to improve the absorption at the edge of the crystal rod, thereby improving uniformity.

[0084] Furthermore, the pump module of the VCSEL side-pumped solid-state laser and the corresponding solid-state laser provided in the embodiments of the present invention utilize the arrangement of the VCSEL chips in the axial direction and the cross section to make the wavelength distribution of a group of VCSEL chips surrounding the crystal rod more uniform, thereby improving the uniformity.

[0085] It should be noted that the above embodiments are merely examples, and the technical solutions of the various embodiments may be combined and are all within the scope of protection of the present invention.

[0086] The terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0087] The pump module and corresponding solid-state laser for a VCSEL side-pumped solid-state laser provided by the present invention are described in detail above. For those skilled in the art, any obvious modification thereof without departing from the essence of the present invention would constitute an infringement of the present invention's patent rights and would incur corresponding legal liability.

Claims

1. A pumping module for a VCSEL side-pumped solid-state laser, comprising a pumping cavity and a crystal rod, characterized in that: The crystal rod is the working rod of the solid-state laser, and the pumping cavity is arranged around the crystal rod; The pumping cavity includes a heat sink and a pumping chip; wherein, the heat sink is a hollow cylinder, and the inner surface of the heat sink is provided with a mounting surface; the mounting surface is a plane parallel to the axis of the heat sink; in a cross-section perpendicular to the axis of the crystal rod, the projections of multiple mounting surfaces form a regular polygon; the number of mounting surfaces is even, including multiple groups of mounting surfaces and corresponding mounting surfaces, and the mounting surfaces and the corresponding mounting surfaces are arranged facing each other; The pumping chip is a VCSEL chip and is arranged on the mounting surface; the light-emitting directions of the pumping chips located on the mounting surface and the light-emitting directions of the pumping chips located on the corresponding mounting surface are aligned in the positive direction with each other.

2. The pumping module according to claim 1, characterized in that: The pumping chip is a VCSEL chip with a top-emitting structure.

3. The pump module according to claim 2, characterized in that It further includes a cooling tube: The axis of the cooling tube coincides with the axis of the crystal rod, is used to surround the crystal rod, and allows cooling gas or liquid to pass through to cool the crystal rod, and is made of a high-transparency material.

4. The pumping module according to claim 3, characterized in that: The cooling tube has a polished outer surface or a frosted outer surface, and the roughness of the frosted outer surface is Ra0.1 - Ra80 μm.

5. The pumping module according to claim 3, characterized in that: The cooling tube has a polished outer surface or a frosted outer surface, and the roughness of the frosted outer surface is Ra0.2 - Ra50 μm.

6. The pumping module according to claim 2, characterized in that: Along the axis of the crystal rod, in multiple cross-sections perpendicular to the axis, the center wavelength difference M of a group of pumping chips located in the same cross-section and the average center wavelength difference N of different groups of pumping chips located in different cross-sections satisfy M < N.

7. The pumping module according to claim 4, characterized in that: Along the axis of the crystal rod, in multiple cross-sections perpendicular to the axis, the center wavelength difference M of a group of pumping chips located in the same cross-section and the average center wavelength difference N of different groups of pumping chips located in different cross-sections satisfy M < N.

8. A pumping module for a VCSEL side-pumped solid-state laser, comprising a pumping cavity and a crystal rod, characterized in that: The crystal rod is the working rod of the solid-state laser, and the pumping cavity is arranged around the crystal rod; The pumping cavity includes a heat sink and a pumping chip; wherein, the heat sink is a hollow cylinder, and the inner surface of the heat sink is provided with a mounting surface; the mounting surface is a plane parallel to the axis of the heat sink; in a cross-section perpendicular to the axis of the crystal rod, the projections of multiple mounting surfaces form a regular polygon; the number of mounting surfaces is even, including multiple groups of mounting surfaces and corresponding mounting surfaces, and the normal directions of the mounting surfaces and the corresponding mounting surfaces are offset; The pumping chip is a VCSEL chip and is arranged on the mounting surface; In a cross-section perpendicular to the axis, in the light-emitting direction of the pump chip located on the mounting surface, the diameter passing through the center of the pump chip and the axis of the crystal rod deviate from each other by a predetermined angle α. The predetermined angle α makes the distance between the chip center normals of the two pump chips on the mounting surface and the corresponding mounting surface less than the diameter of the crystal rod.

9. The pump module according to claim 8, wherein: The pump chip is a VCSEL chip with a top-emitting structure.

10. The pump module according to claim 9, wherein It further includes a cooling tube: The axis of the cooling tube coincides with the axis of the crystal rod, is used to surround the crystal rod, and allows cooling gas or liquid to pass through to cool the crystal rod, and is made of a highly transparent material.

11. The pump module according to claim 10, wherein: The cooling tube has a polished outer surface or a frosted outer surface, and the roughness of the frosted outer surface is Ra0.1 to Ra80 μm.

12. The pump module according to claim 11, wherein: The cooling tube has a polished outer surface or a frosted outer surface, and the roughness of the frosted outer surface is Ra0.2 to Ra50 μm.

13. The pump module according to claim 9, wherein: Along the axis of the crystal rod, in a plurality of cross-sections perpendicular to the axis, the center wavelength gap M of a group of pump chips located in the same cross-section, and the average center wavelength gap N of different groups of pump chips located in different cross-sections satisfy M < N.

14. The pump module according to claim 11, wherein: Along the axis of the crystal rod, in a plurality of cross-sections perpendicular to the axis, the center wavelength gap M of a group of pump chips located in the same cross-section, and the average center wavelength gap N of different groups of pump chips located in different cross-sections satisfy M < N.

15. A solid-state laser, characterized in that It includes the pump module according to any one of claims 1 to 14, and an output mirror and a reflector; wherein, The reflector and the output mirror are located on opposite sides of the pump module, and a resonant cavity is formed between the reflector and the output mirror, The output mirror is arranged in the light-emitting direction of the resonant cavity for emitting light.

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