Composite cavity for homogenizing light spot

Abstract

The present application belongs to the field of pulse laser technology, and particularly relates to a compound cavity for homogenizing a light spot. The compound cavity comprises a concave conical mirror, a laser module, an electro-optic Q-switching device and a Gauss mirror arranged in sequence along an optical path, wherein the Gauss mirror is a concave-convex conical output mirror, and the concave conical mirror and the Gauss mirror form a compound cavity with a central positive-branch confocal unstable cavity having a fixed magnification and a periphery being a traveling wave amplification area. The geometric loss is reduced to be basically ignored when the concave conical mirror is combined with the Gauss mirror, the central unstable cavity structure with a fixed magnification is used in the compound cavity structure, and the periphery uses the conical mirror for parallel amplification. Therefore, the present application can be equivalent to a central resonance and periphery amplification, and has a high energy extraction efficiency, and the stability of the cavity is increased, so that the laser with the compound cavity structure has the characteristics of simple structure, good beam quality, high efficiency, high output energy and the like.

Description

Technical Field

[0001] This invention belongs to the field of pulsed laser technology, and specifically relates to a composite cavity for homogenizing laser spots. Background Technology

[0002] High-beam-quality, high-energy pulsed lasers have crucial applications in scientific research, nonlinear frequency conversion, and industrial processing. Q-switching is the most common technique for obtaining high-energy pulsed lasers. Using Q-switching, pulsed laser outputs with pulse widths ranging from hundreds of picoseconds to hundreds of nanoseconds and pulse repetition frequencies from a few kHz to hundreds of kHz can be achieved. The application of Q-switching has enabled the generation of laser pulses with peak power exceeding megawatts, making lasers extremely powerful coherent light sources. This has led to the development of new optical branches such as nonlinear optics and has also driven the development of application technologies such as lidar, laser ranging, high-speed photography, and nuclear fusion.

[0003] There are two main pumping methods for solid-state pulsed lasers: end-pumping and side-pumping. Laser crystals are primarily available in three shapes: rod-shaped, slab-shaped, and disk-shaped. The advantage of side-pumping structures lies in their ability to couple high-power pump radiation into the laser medium through a simple structure, thus achieving high-power laser output. Compared to slab-shaped side-pumped gain media, rod-shaped side-pumped gain media offer advantages such as simpler cooling structures and lower cost. Therefore, side-pumped laser modules are an important research tool for obtaining high-energy pulsed lasers. However, due to differences in the cooling structure and radial heat generation of rod-shaped crystals, the radial thermal focal length varies, affecting the final beam quality. Traditional unstable cavities have relatively few resonant frequencies at the outer edge of the crystal rod, resulting in insufficient energy extraction. Furthermore, resonant cavities typically have a threshold, preventing the extraction of energy below this threshold. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a composite cavity for homogenizing the beam spot, thereby solving the problem that existing side-pumped laser modules suffer from different radial thermal focal lengths of the crystal rods due to variations in the cooling structure of the rod-shaped crystal and the radial heat generation of the crystal, which in turn affects the final beam quality.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The present invention provides a composite cavity for homogenizing light spots, comprising a concave conical mirror, a laser module, an electro-optic Q-switching device and a Gaussian mirror arranged sequentially along the optical path, wherein the Gaussian mirror is a concave-convex conical output mirror, and the concave conical mirror and the Gaussian mirror constitute a composite cavity with a central positive branch confocal unstable cavity having a fixed magnification and a peripheral traveling wave amplification region.

[0007] The concave conical mirror includes a concave mirror I located on the front surface and an annular conical mirror I disposed around the concave mirror I;

[0008] The Gaussian mirror includes a curvature region at the center and an annular conical mirror II disposed around the curvature region, wherein the curvature region includes a convex mirror and a concave mirror II disposed in parallel.

[0009] The concave mirror I of the concave conical mirror and the curvature region of the Gaussian mirror form the positive branch confocal unstable cavity; the traveling wave amplification region is formed between the annular conical mirror I and the annular conical mirror II.

[0010] The laser module is a side-pumped laser structure with a laser crystal rod at its center. The laser oscillates in the composite cavity and expands from the central region of the laser crystal rod to the wave amplification region. The beam aperture increases uniformly until it fills the entire laser crystal rod, and finally, a pulsed laser with high pulse energy and high beam quality is output by a Gaussian mirror.

[0011] The laser crystal rod is a crystal, glass, or ceramic doped with Nd ions; or a crystal, glass, or ceramic doped with Yb ions; or a crystal, glass, or ceramic doped with Er ions; or a crystal, glass, or ceramic doped with Tm ions, etc.

[0012] The Nd-doped crystal is neodymium-doped yttrium aluminum garnet, neodymium-doped yttrium vanadate, neodymium-doped gadolinium gallium garnet, neodymium-doped lithium yttrium fluoride, neodymium-doped yttrium aluminate, or neodymium-doped strontium fluorophosphate.

[0013] The laser crystal rod has a diameter of D. It is uniformly divided into m concentric rings along its diameter. The diameter of the innermost ring is d1, and this diameter is equal to the width of the curvature region of the Gaussian mirror. The diameter of the second ring is d2 = d1 + (D - d1) / (m - 1), and the diameter of the nth ring is d... n =d1+(D-d1)•(n-1) / (m-1), satisfying: D-d1=d1•(M-1)•m, where m and n are integers ≥2, and m≥n, and M is the fixed magnification of the positive branch confocal unstable cavity.

[0014] The radii of curvature of the convex mirror and the concave mirror II at the same position are equal, both being r1; the vertical distance from the curvature edge of the convex mirror and the concave mirror II to the center point is d1 / 2; the annular conical mirror II is perpendicular to the surface normal of the curvature edge of the convex mirror and the concave mirror II; at this time, the incident angle of the light is θ, and tanθ=d1 / r1.

[0015] The concave conical mirror is a highly reflective mirror, and its rear surface is a plane mirror. The surface of the concave mirror I is coated with a dielectric film that is highly reflective to the laser wavelength.

[0016] The concave mirror I has a radius of curvature of r2 and a perpendicular distance of M•d1 / 2 from the edge of the curvature to the center point. The annular conical mirror I is perpendicular to the surface normal of the edge of the concave mirror I. The incident angle of the light rays on the annular conical mirror I is θ, and tanθ=d1 / r1.

[0017] The concave surface of the Gaussian mirror is coated with a dielectric film that provides gradually varying reflectivity for laser wavelength, with reflectivity R(w) = R max •exp[-2•(w / w m ) 2 ], where w is the radial position on the Gaussian mirror, and the central peak reflectivity is R. max Width is w m The convex mirror is coated with a dielectric film that enhances the light transmittance of laser wavelengths.

[0018] The electro-optic Q-switching device includes a polarizer, a quarter-wave plate, and a Pockel cell arranged sequentially along the optical path. The electro-optic Q-switching device is used to achieve pulsed laser output with nanosecond-level pulse width.

[0019] The advantages and beneficial effects of this invention are: the composite cavity for homogenizing the light spot provided by this invention can obtain high beam quality and high energy pulse lasers. It has the characteristics of high beam quality, high efficiency, simple structure, good amplification and reliable use, and can be widely used in scientific research, nonlinear frequency conversion, industrial processing and other fields.

[0020] To address the issues of poor beam quality and low energy output from existing side-pumped laser modules, this invention employs a composite cavity structure with a homogenized beam pattern, which better homogenizes the thermal inhomogeneities of the crystal rod. The geometric loss from combining a concave conical mirror with a Gaussian mirror is reduced to negligible levels. The composite cavity structure uses a non-stable cavity with a fixed magnification at its center, while the outer ring uses conical mirrors for parallel amplification. Therefore, this invention can be equivalent to a central resonant structure with outer ring amplification, similar to an oscillating amplification method. The outer edge also undergoes double-layer extraction, resulting in high energy extraction efficiency. This high energy extraction efficiency increases cavity stability, giving the laser with this composite cavity structure the characteristics of simple structure, good beam quality, high efficiency, and high output energy.

[0021] In this invention, the aperture (d1) and magnification (M) of the central region of the Gaussian mirror, together with the crystal rod aperture (D), determine the size of the magnified spot in each cycle of the amplification section (d1•(M-1) / 2) and the number of cycles m, satisfying: D-d1=d1•(M-1)•m, where m is an integer ≥2. When the magnified size in each cycle is smaller and the number of cycles is larger, energy can be extracted better, and the thermal lensing effect of the entire crystal can be homogenized. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a composite cavity for homogenizing light spots according to the present invention;

[0023] Figure 2 This is a schematic diagram of the concave conical mirror in this invention;

[0024] Figure 3 This is a schematic diagram of the Gaussian mirror structure in this invention;

[0025] Figure 4 This is a schematic diagram of the cavity mirror curvature of a composite cavity for homogenizing light spots according to the present invention;

[0026] Figure 5 This is a schematic cross-sectional view of the rod-shaped crystal in this invention;

[0027] In the figure: 1. Concave conical mirror, 2. Laser module, 3. Polarizer, 4. Quarter-wave plate, 5. Pockels cell, 6. Gaussian mirror, 11. Concave mirror I, 12. Ring conical mirror I, 13. Plane mirror, 21. Laser crystal rod, 61. Convex mirror, 62. Ring conical mirror II, 63. Concave mirror II. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0029] like Figure 1 As shown, the present invention provides a composite cavity for homogenizing a light spot, comprising a concave conical mirror 1, a laser module 2, an electro-optic Q-switching device, and a Gaussian mirror 6 arranged sequentially along the optical path. The Gaussian mirror 6 is a concave-convex conical output mirror. The concave conical mirror 1 and the Gaussian mirror 6 form a composite cavity with a centrally located, positively oriented confocal unstable cavity with a fixed magnification, and a peripheral traveling-wave amplification region. The composite cavity structure uses a fixed-magnification unstable cavity structure at its center, and the outer ring uses conical mirrors for parallel amplification. Therefore, the present invention can be equivalent to a central resonance with outer ring amplification, resulting in high energy extraction efficiency and increased cavity stability.

[0030] like Figure 1 As shown in the embodiments of the present invention, the electro-optic Q-switching device is used to achieve pulsed laser output with nanosecond-level pulse widths. Specifically, the optical Q-switching device includes a polarizer 3, a quarter-wave plate 4, and a Pockels cell 5 arranged sequentially along the optical path. The electro-optic Q-switching device can achieve pulsed laser output with nanosecond-level pulse widths.

[0031] like Figure 2-4As shown, in an embodiment of the present invention, the concave conical mirror 1 includes a concave mirror I11 located on the front surface and an annular conical mirror I12 disposed around the concave mirror I11; the Gaussian mirror 6 includes a curvature region located at the center and an annular conical mirror II62 disposed around the curvature region, wherein the curvature region includes a convex mirror 61 and a concave mirror II63 arranged in parallel; the concave mirror I11 of the concave conical mirror 1 and the curvature region of the Gaussian mirror 6 form a positive branch confocal unstable cavity, which has a fixed magnification; a traveling wave amplification region is formed between the annular conical mirror I12 and the annular conical mirror II62 to amplify the laser in parallel. In the composite cavity composed of the concave conical mirror 1 and the Gaussian mirror 6, the curvature region at the center of the two mirrors corresponds to a magnification of M.

[0032] In the embodiments of the present invention, the laser module 2 is a side-pumped laser structure with a laser crystal rod 21 at its center. The laser oscillates in the composite cavity and expands from the central region of the laser crystal rod 21 to the wave amplification region. The beam aperture increases uniformly until it fills the entire laser crystal rod 21. Finally, a pulsed laser with high pulse energy and high beam quality is output by the Gaussian mirror 6.

[0033] Specifically, the laser crystal rod 21 is a crystal, glass, or ceramic doped with Nd ions; or a crystal, glass, or ceramic doped with Yb ions; or a crystal, glass, or ceramic doped with Er ions; or a crystal, glass, or ceramic doped with Tm ions, etc. Preferably, the Nd-doped crystal is neodymium-doped yttrium aluminum garnet, neodymium-doped yttrium vanadate, neodymium-doped gadolinium gallium garnet, neodymium-doped lithium yttrium fluoride, neodymium-doped yttrium aluminate, or neodymium-doped strontium fluorophosphate.

[0034] like Figure 4-5 As shown in the embodiment of the present invention, the diameter of the laser crystal rod 21 is D. The laser crystal rod 21 is uniformly divided into m concentric rings along the diameter direction. The diameter of the innermost ring is d1, and the diameter of the innermost ring is equal to the width of the curvature region of the Gaussian mirror 6. The diameter of the second ring is d2 = d1 + (D - d1) / (m - 1), and the diameter of the nth ring is d... n =d1+(D-d1)•(n-1) / (m-1), satisfying: D-d1=d1•(M-1)•m, where m and n are integers ≥2, and m≥n, and M is the fixed magnification of the positive branch confocal unstable cavity.

[0035] In the embodiments of the present invention, the radii of curvature of the convex mirror 61 and the concave mirror II 63 at the same position are equal in size, both being r1; the vertical distance from the curvature edge of the convex mirror 61 and the concave mirror II 63 to the center point is d1 / 2, and the annular conical mirror II 62 is perpendicular to the surface normal of the curvature edge of the convex mirror 61 and the concave mirror II 63. At this time, the incident angle of the light is θ, and tanθ = d1 / r1.

[0036] In an embodiment of the present invention, the concave conical mirror 1 is a highly reflective mirror, and its rear surface is a plane mirror 13. The surface of the concave mirror I11 is coated with a dielectric film that is highly reflective to the laser wavelength. The radius of curvature of the concave mirror I11 is r2, and the vertical distance from the edge of the curvature to the center point is M•d1 / 2. The annular conical mirror I12 is perpendicular to the surface normal of the edge of the concave mirror I11, and the incident angle of the light on the annular conical mirror I12 is θ, and tanθ=d1 / r1.

[0037] In an embodiment of the present invention, the concave surface of the Gaussian mirror 6 is coated with a dielectric film with a gradually varying reflectivity for laser wavelength, wherein the reflectivity R(w) = R max •exp[-2•(w / w m ) 2 ], where w is the radial position on the Gaussian mirror, and the central peak reflectivity is R. max Width is w m The convex mirror 61 is coated with a dielectric film that enhances the light transmittance of laser wavelengths.

[0038] To address the issues of poor pulsed laser output beam quality and low energy in existing side-pumped laser modules, this invention employs a composite cavity structure with a homogenized beam pattern, which better homogenizes the thermal inhomogeneity of the crystal rod. Geometric losses from combining concave conical mirrors and Gaussian mirrors are reduced to negligible levels. The composite cavity structure uses a fixed-magnification unstable cavity at its center, while the outer ring uses conical mirrors for parallel amplification. Therefore, this invention can be equivalent to a central resonance with outer-ring amplification. Most of the crystal rod undergoes double energy extraction, with only a small portion undergoing single energy extraction during the final output of the outermost layer. Traditional unstable cavities have relatively few resonance cycles at the outer edge of the crystal rod, resulting in insufficient energy extraction. Furthermore, resonant cavities typically have a threshold, preventing energy extraction below this threshold. This solution, however, uses an amplification-like method, with double extraction at the outer edge, resulting in higher energy extraction efficiency. A high-magnification unstable cavity can be used in the central region, increasing cavity stability. A smaller aperture in the central resonant region leads to better beam quality in the seed beam portion. The aperture (d1) and magnification (M) of the central region of the Gaussian mirror, together with the aperture (D) of the crystal rod, determine the size of the magnified spot in each cycle of the amplification section (d1•(M-1) / 2) and the number of cycles m, satisfying: D-d1=d1•(M-1)•m, where m is an integer ≥2. When the magnified size in each cycle is smaller and the number of cycles is larger, energy can be extracted better, and the thermal lensing effect of the entire crystal can be homogenized.

[0039] This invention has the advantages of relatively easy cavity mirror processing and good feasibility, and is particularly suitable for large-diameter crystal rods. Therefore, it is expected to obtain high beam quality and high-energy pulsed laser output, which can meet important applications in scientific research, nonlinear frequency conversion, industrial processing and other fields. Example

[0040] The first embodiment of the present invention is as follows: Figure 1 As shown, this invention provides a composite cavity for homogenizing a light spot, comprising: a concave conical mirror 1, a laser module 2, a polarizer 3, a quarter-wave plate 4, a Pockel cell 5, and a Gaussian mirror 6, placed along a straight line (z-axis); the polarizer 3, quarter-wave plate 4, and Pockel cell 5 form an electro-optic Q-switching device; the concave conical mirror 1 and the Gaussian mirror 6 form a composite cavity for homogenizing the light spot, with the center of the two mirrors forming a positive branch confocal unstable cavity with a fixed magnification M=2 composed of a curvature region, and the outer conical region forming a traveling wave amplification region. The focal point of the positive branch confocal unstable cavity is F1, and the distance between the concave mirror 111 and the convex mirror 61 is L.

[0041] Laser module 2 is a side-pumped laser structure with a laser crystal rod 12 at its center. The material is Nd:YAG crystal with a diameter D=7mm, a length of 125mm, and a doping of 0.6 at.%. The laser crystal rod 12 is evenly divided into 5 concentric rings along the diameter direction. The diameter of the innermost ring is d1=1mm, the diameter of the second ring is 2mm, the diameter of the third ring is 3mm, the diameter of the fourth ring is 4mm, ..., and the diameter of the outermost ring is 7mm.

[0042] Gaussian mirror 6 is a concave-convex cone-shaped output mirror, and the central curvature region is a concave-convex mirror. The radius of curvature at the same position on the concave and convex surfaces is equal in size, r1=1m. The vertical distance from the edge of the curvature to the center point is d1 / 2=0.5mm. The surface extending outward to the edge of the lens is a conical mirror, which is perpendicular to the normal of the surface. At this time, the angle of incidence is θ, and tanθ=d1 / r1, θ=1mrad.

[0043] The rear surface of the concave conical mirror 1 is a plane mirror 13. The radius of curvature of the concave region on the front surface is r2 = 2m, and the perpendicular distance from the edge of the curvature to the center point is M•d1 / 2 = 1m. The surface extending outwards to the edge of the mirror is a conical mirror, and the angle between the conical surface and the perpendicular line to the normal of the surface is θ = 1mrad. Furthermore, it can be deduced that the cavity length of the composite cavity for homogenizing the light spot is 1m.

[0044] The concave surface of Gaussian mirror 6 is coated with a dielectric film that provides gradually varying reflectivity to the laser wavelength, with reflectivity R(w) = R max •exp[-2•(w / w m ) 2 ], where w is the radial position on the Gaussian mirror, and the central peak reflectivity is R. max =30%, width is w m =2.5mm, the convex surface of the mirror is coated with a dielectric film that enhances the transmission of laser wavelength (transmittance T≥99.9%).

[0045] The concave conical mirror 1 is a plano-concave high-reflectivity mirror, and the concave surface of the mirror is coated with a dielectric film that is highly reflective to the laser wavelength (reflectivity R≥99.9%).

[0046] The laser oscillates in the composite cavity with a homogenized beam. Starting from the center region of the crystal rod, the beam aperture gradually and uniformly increases, with diameters of 1 mm, 2 mm, 3 mm, and 4 mm until it fills the entire crystal rod (7 mm). Finally, it outputs a pulsed laser with large pulse energy and high beam quality.

[0047] In summary, to address the issues of poor pulsed laser output beam quality and low energy in existing side-pumped laser modules, this invention employs a composite cavity structure with a homogenized beam pattern. This structure better homogenizes the thermal inhomogeneity of the crystal rod, thereby improving energy extraction from the outer crystal rod. Geometric losses when combined with a Gaussian mirror can be reduced to negligible levels. The center of the composite cavity uses an unstable cavity structure with a fixed magnification, while the outer ring uses conical mirrors for parallel amplification. This scheme can be equivalent to a central resonance with outer ring amplification. Similar to an oscillating amplification method, the outer edge also undergoes double-layer extraction, resulting in high energy extraction efficiency. The central region can use an unstable cavity with a relatively high magnification, increasing cavity stability. The smaller the aperture of the central resonance region, the better the beam quality of the seed beam. Smaller amplification size per cycle and a larger number of cycles allow for better energy extraction and better homogenization of the thermal lensing effect across the entire crystal.

[0048] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, extensions, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A composite cavity for homogenizing light spots, characterized in that, It includes a concave conical mirror (1), a laser module (2), an electro-optic Q-switching device and a Gaussian mirror (6) arranged sequentially along the optical path. The Gaussian mirror (6) is a concave-convex conical output mirror. The concave conical mirror (1) and the Gaussian mirror (6) together form a composite cavity with a central positive branch confocal unstable cavity with a fixed magnification and an outer traveling wave amplification region.

2. The composite cavity for homogenizing the light spot according to claim 1, characterized in that, The concave conical mirror (1) includes a concave mirror I (11) located on the front surface and an annular conical mirror I (12) disposed around the concave mirror I (11). The Gaussian mirror (6) includes a curvature region located at the center and an annular conical mirror II (62) disposed around the curvature region, wherein the curvature region includes a convex mirror (61) and a concave mirror II (63) disposed in parallel. The concave mirror I (11) of the concave conical mirror (1) and the curvature region of the Gaussian mirror (6) form the positive branch confocal unstable cavity; the traveling wave amplification region is formed between the annular conical mirror I (12) and the annular conical mirror II (62).

3. The composite cavity for homogenizing the light spot according to claim 1, characterized in that, The laser module (2) is a side-pumped laser structure with a laser crystal rod (21) at its center. The laser oscillates in the composite cavity and expands from the central region of the laser crystal rod (21) to the wave amplification region. The beam aperture increases uniformly until it fills the entire laser crystal rod (21). Finally, a pulsed laser with high pulse energy and high beam quality is output by the Gaussian mirror (6).

4. The composite cavity for homogenizing the light spot according to claim 3, characterized in that, The laser crystal rod (21) is a crystal, glass or ceramic doped with Nd ions; or a crystal, glass or ceramic doped with Yb ions; or a crystal, glass or ceramic doped with Er ions; or a crystal, glass or ceramic doped with Tm ions.

5. The composite cavity for homogenizing the light spot according to claim 4, characterized in that, The Nd-doped crystal is neodymium-doped yttrium aluminum garnet, neodymium-doped yttrium vanadate, neodymium-doped gadolinium gallium garnet, neodymium-doped lithium yttrium fluoride, neodymium-doped yttrium aluminate, or neodymium-doped strontium fluorophosphate.

6. The composite cavity for homogenizing the light spot according to claim 3, characterized in that, The laser crystal rod (21) has a diameter of D. The laser crystal rod (21) is uniformly divided into m concentric rings along the diameter direction. The diameter of the innermost ring is d1, and the diameter of the innermost ring is equal to the width of the curvature region of the Gaussian mirror (6). The diameter of the second ring is d2 = d1 + (D - d1) / (m - 1), and the diameter of the nth ring is d n =d1+(D-d1)•(n-1) / (m-1), satisfying: D-d1=d1•(M-1)•m, where m and n are integers ≥2, and m≥n, and M is the fixed magnification of the positive branch confocal unstable cavity.

7. The composite cavity for homogenizing the light spot according to claim 2, characterized in that, The radii of curvature of the convex mirror (61) and the concave mirror II (63) at the same position are equal, both being r1; the vertical distance from the curvature edge of the convex mirror (61) and the concave mirror II (63) to the center point is d1 / 2; the annular conical mirror II (62) is perpendicular to the surface normal of the curvature edge of the convex mirror (61) and the concave mirror II (63); at this time, the incident angle of the light is θ, and tanθ=d1 / r1.

8. The composite cavity for homogenizing the light spot according to claim 2, characterized in that, The concave conical mirror (1) is a highly reflective mirror, and its rear surface is a plane mirror (13). The mirror surface where the concave mirror I (11) is located is coated with a dielectric film that is highly reflective to the laser wavelength. The radius of curvature of the concave mirror I (11) is r2, and the vertical distance from the edge of the curvature to the center point is M•d1 / 2; the annular conical mirror I (12) is perpendicular to the surface normal of the edge of the concave mirror I (11), and the incident angle of the light on the annular conical mirror I (12) is θ, and tanθ=d1 / r1.

9. The composite cavity for homogenizing the light spot according to claim 4, characterized in that, The concave surface of the Gaussian mirror (6) is coated with a dielectric film that provides gradually varying reflectivity for laser wavelength, with reflectivity R(w) = R max •exp[-2•(w / w m ) 2 ], where w is the radial position on the Gaussian mirror, and the central peak reflectivity is R. max Width is w m The convex mirror (61) is coated with a dielectric film that enhances the transmission of laser wavelength.

10. The composite cavity for homogenizing the light spot according to claim 1, characterized in that, The electro-optic Q-switching device includes a polarizer (3), a quarter-wave plate (4), and a Pockel cell (5) arranged sequentially along the optical path. The electro-optic Q-switching device is used to achieve pulsed laser output with nanosecond-level pulse width.

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