A fully solid-state 355nm laser

Abstract

The present application discloses a fully solid-state 355nm laser, including a pump source, a beam coupling system, a laser resonant cavity, and an output system; the beam coupling system is arranged on the outgoing optical path of the pump source, the laser resonant cavity is arranged on the outgoing optical path of the beam coupling system, a gain medium and adjacently placed frequency doubling crystals and sum frequency crystals are arranged in the laser resonant cavity, and the output system is arranged on the outgoing optical path of the sum frequency crystal; wherein the optical axis direction of the frequency doubling crystal is inconsistent with the optical axis direction of the sum frequency crystal, thereby utilizing the walk-off generated by the frequency doubling process to compensate for the walk-off generated by the sum frequency process. The present application realizes walk-off compensation by making the optical axis directions of the frequency doubling crystal and the sum frequency crystal inconsistent, and amplifies the spot radius of the fundamental frequency light at the sum frequency crystal while ensuring the high-power output of the 355nm ultraviolet laser, thereby improving the service life of the crystal.

Description

Technical Field

[0001] The present application relates to the field of laser technology, and more specifically, to an all-solid-state 355nm laser. Background Art

[0002] High-power, high-beam-quality all-solid-state 355nm ultraviolet lasers have been widely used in precision processing, biomedicine, optical manufacturing, optical sensing and other fields due to their short wavelength, easy focusing and high energy. The most commonly used technical means to achieve 355nm ultraviolet laser output is to use a master oscillator power amplifier (MOPA) to amplify the 1064nm seed light in a single or multi-stage manner, and then obtain it after frequency conversion outside the cavity. In this method, although the high-power output of the 355nm ultraviolet laser can be guaranteed, the overall system is relatively complex, which is not conducive to obtaining a highly stable ultraviolet laser. In addition, in order to improve the conversion efficiency of the frequency conversion process, the waist spot size of the fundamental frequency light and the doubled frequency light at the frequency conversion crystal is usually reduced to increase the power density of the two, which causes the coating on the end face of the frequency conversion crystal to be easily damaged under long-term irradiation of high-power density lasers.

[0003] Compared with the extra-cavity sum-frequency technology, the intra-cavity sum-frequency process can not only make full use of the advantages of the high power density of the intra-cavity fundamental frequency light, but also the obtained laser has a compact overall structure and high stability. It is one of the effective means to achieve high-power and high-stability all-solid-state 355nm ultraviolet laser.

[0004] In the traditional intracavity sum frequency scheme, the frequency doubling crystal adopts the type I non-critical phase matching method, and the sum frequency crystal adopts the type II critical phase matching method. In this way, although the 1064nm fundamental frequency light and the 532nm frequency doubling light do not walk off during the frequency doubling process, the 1064nm fundamental frequency light and the 532nm frequency doubling light will walk off during the sum frequency process and cannot be compensated, which ultimately affects the sum frequency conversion efficiency and the beam quality of the 355nm ultraviolet laser. Based on this problem, one solution is to insert a walk-off compensator in front of the sum frequency crystal, but this results in an additional optical element in the cavity, and the loss of the fundamental frequency light increases. In order to achieve more compensation, the walk-off compensator makes the deflection angle of the 532nm frequency doubling light need to be larger, which leads to a certain limit on the selection of the size of the intracavity sum frequency crystal. When the divergence angle of the fundamental frequency beam is large, it is impossible to reasonably use the smaller waist spot in space to simultaneously ensure high sum frequency conversion efficiency and high frequency doubling conversion efficiency. Another solution is to divide the sum frequency crystal into two crystals of the same length and place them close together with their optical axes in different directions. However, when the 355nm ultraviolet laser is output at high power, this method almost doubles the probability of damage to the coating layer on the end face of the sum frequency crystal, which is not conducive to the long-term use of the sum frequency crystal. Therefore, it is only suitable for use with 355nm ultraviolet lasers with lower output power.

[0005] In addition, in the combination of type I non-critical phase matching and type II critical phase matching, since the frequency doubling crystal adopts type I non-critical phase matching, its matching temperature is within the range of 140°-150°, while the sum frequency crystal adopts type II critical phase matching, and its matching temperature is within the normal temperature range. At this time, when the two nonlinear crystals are placed close to each other, due to the huge temperature difference, there is serious heat transfer between the two non-linear crystals and between the non-linear crystal temperature control furnace, resulting in uneven temperature distribution of the sum frequency crystal, which in turn affects the sum frequency conversion efficiency. In order to reduce the impact of temperature difference on sum frequency conversion efficiency, usually, the matching temperature of the sum frequency crystal in this matching combination is generally within the range of 60°-70°, which requires higher temperature control capability of normal temperature control equipment, and at the same time, the heat insulation treatment between the two crystals must be done well, and the overall operation is difficult. Summary of the invention

[0006] The present application provides an all-solid-state 355nm laser, in which the optical axis directions of the frequency doubling crystal and the sum frequency crystal are not arranged in the same direction, so that the 1064nm fundamental frequency light and the 532nm frequency doubling light separated due to walk-off in the frequency doubling crystal are reunited when passing through the sum frequency crystal, so that the overlapping area of ​​the two beams in the sum frequency crystal becomes larger, and walk-off compensation is achieved, and finally a high-power 355nm ultraviolet laser output can be obtained, thereby avoiding the adverse effects of the walk-off compensator and the split sum frequency crystal, and not only improving the sum frequency conversion efficiency but also improving its beam quality. In addition, due to the improvement of the conversion efficiency, the advantage of the high power density of the fundamental frequency light in the resonant cavity can be fully utilized, and the spot radius of the fundamental frequency light at the sum frequency crystal is enlarged while ensuring the high-power output of the 355nm ultraviolet laser, thereby improving the service life of the crystal. At the same time, the large spot can effectively reduce the thermal effect of the nonlinear crystal and improve the beam quality of the harmonics in the cavity when working at high power.

[0007] The present application provides an all-solid-state 355nm laser, including a pump source, a beam coupling system, a laser resonant cavity, and an output system;

[0008] The beam coupling system is arranged on the outgoing optical path of the pump source, the laser resonant cavity is arranged on the outgoing optical path of the beam coupling system, a gain medium and adjacently placed frequency doubling crystals and sum frequency crystals are arranged in the laser resonant cavity, and the output system is arranged on the outgoing optical path of the sum frequency crystal;

[0009] The optical axis direction of the frequency doubling crystal is inconsistent with the optical axis direction of the sum frequency crystal, so the walk-off generated in the frequency doubling process is used to compensate for the walk-off generated in the sum frequency process.

[0010] Preferably, the frequency doubling crystal is a nonlinear crystal of type I critical phase matching mode, and the sum frequency crystal is a nonlinear crystal of type II critical phase matching mode.

[0011] Preferably, both the frequency doubling crystal and the sum frequency crystal are nonlinear crystals with double-ended vertical cut surfaces.

[0012] Preferably, the laser resonant cavity comprises a first plano-convex mirror, a second plano-convex mirror and a gain medium placed between the first plano-convex mirror and the second plano-convex mirror, and the output light of the beam coupling system enters the laser resonant cavity through the first plano-convex mirror.

[0013] Preferably, the laser resonant cavity also includes a first plane mirror and a second plane mirror, an acousto-optic Q-switch is provided on the optical path between the first plano-convex mirror and the first plane mirror, and a frequency doubling crystal and a sum frequency crystal are arranged on the optical path between the second plano-convex mirror and the second plane mirror. Compared with the sum frequency crystal, the frequency doubling crystal is closer to the second plane mirror.

[0014] Preferably, the output system includes a third plane mirror and a fourth plane mirror, the third plane mirror is located on the main light path between the second plano-convex mirror and the sum frequency crystal and the angle between the third plane mirror and the main light path is 45°, and the fourth plane mirror is arranged outside the laser resonant cavity and located on the reflected light path of the third plane mirror.

[0015] Preferably, the laser resonant cavity also includes a first plano-concave mirror and a second plano-concave mirror, an acousto-optic Q-switch is provided on the optical path between the second plano-convex mirror and the first plano-concave mirror, a isolator is provided on the optical path between the first plano-convex mirror and the second plano-concave mirror, a frequency doubling crystal and a sum frequency crystal are arranged on the optical path between the first plano-convex mirror and the second plano-concave mirror, and the frequency doubling crystal is closer to the first plano-concave mirror than the sum frequency crystal.

[0016] Preferably, the output system comprises a fifth plane mirror, which is arranged outside the laser resonance cavity and located on the output light path of the second plano-concave mirror.

[0017] Preferably, the all-solid-state 355nm laser further includes a convex lens and a sixth plane mirror, the convex lens is arranged outside the laser resonant cavity and located on the output light path of the second plano-convex mirror, and the convex lens is located between the second plano-convex mirror and the sixth plane mirror.

[0018] Preferably, the phase matching angle of the frequency doubling crystal is θ=90°, Φ=(10.8°-11.6°); the phase matching angle of the sum frequency crystal is θ=(42.2°-43.4°), Φ=90°.

[0019] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0021] Figure 1A structural diagram of an embodiment of a standing wave cavity of an all-solid-state 355nm laser provided in this application;

[0022] Figure 2 A schematic diagram of walk-off compensation between a frequency doubling crystal and a sum frequency crystal in a standing wave cavity provided by the present application;

[0023] Figure 3 A schematic diagram of the walk-off superposition between the frequency doubling crystal and the sum frequency crystal in the standing wave cavity provided by the present application;

[0024] Figure 4 A structural diagram of an embodiment of a traveling wave cavity of an all-solid-state 355nm laser provided in this application;

[0025] Figure 5 Structural diagram of walk-off compensation between frequency doubling crystal and sum frequency crystal in the traveling wave cavity provided by the present application

[0026] Figure 6 This is a structural diagram of the walk-off superposition between the frequency doubling crystal and the sum frequency crystal in the traveling wave cavity provided by the present application.

[0027] The following are marked in the figure:

[0028] 1-pump source; 2-beam coupling system; 3-laser resonant cavity; 4-gain medium; 5-acousto-optic Q-switch; 6-frequency doubling crystal; 7-sum frequency crystal; 8-third plane mirror; 9-fourth plane mirror; 10-seventh plane mirror; 11-sixth plane mirror; 12-convex lens; 13-first plane mirror; 14-first plano-convex mirror;

[0029] 15-second plano-convex mirror; 16-second plane mirror; 17-a small amount of 1064nm fundamental frequency light and 532nm double frequency light remaining from 355nm laser; 18-355nm ultraviolet laser; 19-gain medium; 20-TGG isolator; 21-double frequency crystal; 22-sum frequency crystal; 23-first plano-convex mirror; 24-second plano-convex mirror; 25-first plano-concave mirror; 26-second plano-concave mirror; 27-acoustic-optic Q-switch; 28-fifth plane mirror. DETAILED DESCRIPTION

[0030] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0031] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0032] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0033] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0034] The present application provides a fully solid-state 355nm laser, in which the optical axis directions of the frequency doubling crystal and the sum frequency crystal are inconsistent, so that the 1064nm fundamental frequency light and the 532nm frequency doubling light separated due to walk-off in the frequency doubling crystal are reunited when passing through the sum frequency crystal, so that the overlapping area of ​​the two beams in the sum frequency crystal becomes larger, and walk-off compensation is achieved, and finally a high-power 355nm ultraviolet laser output can be obtained, thereby avoiding the adverse effects of the walk-off compensator and the split sum frequency crystal, and not only the sum frequency conversion efficiency can be improved, but also its beam quality can be improved. In addition, due to the improvement of the conversion efficiency, the advantage of the high power density of the fundamental frequency light in the resonant cavity can be fully utilized, and the spot radius of the fundamental frequency light at the sum frequency crystal is enlarged while ensuring the high power output of the 355nm ultraviolet laser, thereby improving the service life of the crystal. At the same time, the large spot can effectively reduce the thermal effect of the nonlinear crystal, and further improve the beam quality of the harmonics in the cavity when working at high power. In addition, in the present application, both the frequency doubling crystal and the sum frequency crystal are double-ended vertical cut surfaces, which effectively avoids the problem of serious astigmatism of the fundamental frequency light caused by the introduction of the Brewster angle used in the prior art.

[0035] The present application provides a fully solid-state 355nm laser including a pump source, a beam coupling system, a laser resonant cavity, and an output system. The beam coupling system is arranged on the outgoing optical path of the pump source, the laser resonant cavity is arranged on the outgoing optical path of the beam coupling system, a gain medium and adjacently placed frequency doubling crystals and sum frequency crystals are arranged in the laser resonant cavity, and the output system is arranged on the outgoing optical path of the sum frequency crystal. Among them, the optical axis direction of the frequency doubling crystal is inconsistent with the optical axis direction of the sum frequency crystal, so that the walk-off generated by the frequency doubling process is used to compensate for the walk-off generated by the sum frequency process, thereby realizing walk-off compensation.

[0036] Preferably, the frequency doubling crystal is a nonlinear crystal of type I critical phase matching mode, so as to realize the conversion of 1064nm fundamental frequency light to 532nm frequency doubling light. The sum frequency crystal is a nonlinear crystal of type II critical phase matching mode, so as to realize the sum frequency of 1064nm fundamental frequency light and 532nm frequency doubling light to generate 355nm ultraviolet laser.

[0037] The phase matching angle of the frequency doubling crystal is θ=90°, Φ=(10.8°-11.6°). Preferably, for the frequency doubling crystal, Φ=(11.2°-11.6°).

[0038] The phase matching angle of the sum frequency crystal is θ=(42.2°-43.4°), Φ=90°. Preferably, for the sum frequency crystal, θ=(42.2°-42.8°).

[0039] The frequency doubling crystal is of type I critical phase matching, and the sum frequency crystal is of type II critical phase matching. During the nonlinear frequency conversion process, both 1064nm fundamental frequency light and 532nm frequency doubling light will walk off. By optimizing the phase matching angle, the matching temperature of the frequency doubling and sum frequency crystals can be within the range of 20°-30° room temperature. The smaller temperature difference is beneficial for the sum frequency crystal to avoid the temperature difference between the two nonlinear crystals affecting the good temperature distribution of the sum frequency crystal, and objectively improve the temperature control accuracy of normal temperature control, which is beneficial to improve the sum frequency conversion efficiency.

[0040] As an embodiment, the frequency doubling crystal and the sum frequency crystal may be an LBO crystal or a BBO crystal.

[0041] As an embodiment, the pumping mode of the pump source is end-face pumping, the pump source is a semiconductor laser, and the gain medium is Nd:YVO4 crystal.

[0042] Specifically, the laser resonant cavity includes a first plano-convex mirror, a second plano-convex mirror, and a gain medium placed between the first plano-convex mirror and the second plano-convex mirror. The output light of the beam coupling system enters the laser resonant cavity through the first plano-convex mirror. The pump beam output by the pump source is shaped and focused by the coupling system and then incident on the center of the gain medium 4 in the laser resonant cavity, generating 1064nm fundamental frequency light and oscillating in the laser resonant cavity.

[0043] Specifically, the laser resonant cavity may be a standing wave cavity structure or a traveling wave cavity structure of any shape.

[0044] As an example, Figure 1 As shown, the all-solid-state 355nm laser includes a pump source 1, a beam coupling system 2, a laser resonant cavity 3, and an output system. The laser resonant cavity 3 is a standing wave cavity, and the laser resonant cavity 3 includes a first plano-convex mirror 14, a second plano-convex mirror 15, a first plane mirror 13, and a second plane mirror 16. The gain medium 4 is arranged on the optical path between the first plano-convex mirror 14 and the second plano-convex mirror 15, and an acousto-optic Q-switch 5 is arranged on the optical path between the first plano-convex mirror 14 and the first plane mirror 13. The frequency doubling crystal 6 and the sum frequency crystal 7 are arranged on the optical path between the second plano-convex mirror 15 and the second plane mirror 16. Compared with the sum frequency crystal 7, the frequency doubling crystal 6 is closer to the second plane mirror 16.

[0045] like Figure 1As shown, the output system includes a third plane mirror 8 and a fourth plane mirror 9. The third plane mirror 8 is arranged on the main optical path between the second plano-convex mirror 15 and the sum frequency crystal 7 and the angle between the third plane mirror 8 and the main optical path is 45°. The fourth plane mirror 9 is arranged outside the laser resonant cavity 3 and located on the reflected optical path of the third plane mirror 8. A seventh plane mirror 10 is also arranged on the reflected optical path of the fourth plane mirror 9.

[0046] The 1064nm fundamental frequency light generated by the gain medium 4 oscillates in the standing wave cavity, and is modulated by the acousto-optic Q-switching switch 5. The modulated 1064nm fundamental frequency light passes through the frequency doubling crystal 6 twice to convert the 1064nm fundamental frequency light to 532nm frequency doubling light. The 1064nm fundamental frequency light that has not completed frequency doubling passes through the sum frequency crystal 7 for sum frequency with the 532nm frequency doubling light to obtain a 355nm ultraviolet laser. The 1064nm fundamental frequency light continues to oscillate in the laser resonant cavity after being transmitted through the third plane mirror 8, and the 355nm ultraviolet laser, the 532nm frequency-doubled light and a small amount of the remaining 1064nm fundamental frequency light are reflected through the third plane mirror 8 and output from the laser resonant cavity, wherein most of the 532nm frequency-doubled light and a small amount of the 1064nm fundamental frequency light are transmitted through the fourth plane mirror 9 to form a light beam 17, and the 355nm ultraviolet laser, a small amount of the 532nm frequency-doubled light and a very small part of the 1064nm fundamental frequency light are reflected through the fourth plane mirror 9 to reach the seventh plane mirror 10. Since the seventh plane mirror 10 is provided with a high-reflection film for the 355nm ultraviolet laser and a high-transmittance film for the 532nm frequency-doubled light and the 1064nm fundamental frequency light, the 355nm ultraviolet laser is reflected through the seventh plane mirror 10 to form a light beam 18, thereby filtering out the small amount of the 1064nm fundamental frequency light and the 532nm frequency-doubled light remaining in the output light.

[0047] During nonlinear frequency conversion, when the 1064nm fundamental frequency light passes through the type I critical phase-matched frequency doubling crystal, due to the angle matching, the 1064nm fundamental frequency light and the 532nm frequency doubling light produce walk-off in the xy plane, while when the 1064nm fundamental frequency light and the 532nm frequency doubling light pass through the type II critically matched sum frequency crystal, the 1064nm frequency doubling light and the 532nm fundamental frequency light produce walk-off in the yz plane.

[0048] like Figure 3 As shown in the figure, when the optical axis directions of the frequency doubling crystal (located on the right) and the sum frequency crystal (located on the left) are consistent, based on the walk-off between the 1064nm fundamental frequency light and the 532nm frequency doubling light during the frequency doubling process, the walk-off will be further superimposed during the sum frequency process, resulting in a significant reduction in the overlapping area between the frequency doubling light and the fundamental frequency light in the sum frequency crystal, thereby reducing the conversion efficiency of the sum frequency process. Figure 3 In the figure, the coordinate system composed of the x, y, and z axes represents the principal axis coordinate system of the crystal.

[0049] When the optical axis directions of the frequency doubling crystal and the sum frequency crystal are inconsistent, the 1064nm fundamental frequency light and the 532nm frequency doubling light separated due to walk-off in the frequency doubling crystal will reunite after passing through the sum frequency crystal, making the overlapping area of ​​the two light beams in the sum frequency crystal larger, and finally a high-power 355nm ultraviolet laser output can be obtained. Figure 2 An example is shown, in which Figure 2 The y and z axes of the neutral frequency crystal are relative to Figure 3 The y and z axes of the sum frequency crystal are rotated 180°, thereby changing the optical axis direction of the sum frequency crystal, so that the 1064nm fundamental frequency light and the 532nm double frequency light are re-overlapped in the sum frequency crystal, achieving walk-off compensation, thereby improving the conversion efficiency of the sum frequency crystal.

[0050] As another example, Figure 4 As shown, the all-solid-state 355nm laser includes a pump source 1, a beam coupling system 2, a laser resonant cavity 3, and an output system. The laser resonant cavity 3 is a traveling wave cavity, and the laser resonant cavity 3 includes a first plano-convex mirror 23, a second plano-convex mirror 24, a first plano-concave mirror 25, and a second plano-concave mirror 26. The gain medium 19 is arranged between the first plano-convex mirror 23 and the second plano-convex mirror 24. An acousto-optic Q-switching switch 27 is arranged on the optical path between the second plano-convex mirror 24 and the first plano-concave mirror 25. A isolator 20 (such as a TGG crystal) is arranged on the optical path between the first plano-convex mirror 23 and the second plano-concave mirror 26. A frequency doubling crystal 21 and a sum frequency crystal 22 are arranged on the optical path between the first plano-concave mirror 25 and the second plano-concave mirror 26. Compared with the sum frequency crystal 22, the frequency doubling crystal 21 is closer to the first plano-concave mirror 25. As shown in FIG. Figure 4 As shown, the output system includes a fifth plane mirror 28, which is arranged outside the laser resonant cavity 3 and located on the output light path of the second plano-concave mirror 26. The 1064nm fundamental frequency light generated by the gain medium 19 oscillates in the traveling wave cavity and is modulated by the acousto-optic Q-switch 27. The modulated 1064nm fundamental frequency light passes through the frequency doubling crystal 21 to convert the 1064nm fundamental frequency light to the 532nm frequency doubling light. The remaining un-frequency-doubled 1064nm fundamental frequency light in the cavity and the 532nm frequency doubling light pass through the sum frequency crystal 22 for sum frequency, and a 355nm ultraviolet laser is obtained. The 355nm ultraviolet laser passes through the second plano-concave mirror 2 6 is transmitted through the output resonant cavity, thereby separating the generated 355nm ultraviolet laser from the 1064nm fundamental frequency light and the 532nm double frequency light. Subsequently, the 355nm ultraviolet laser is transmitted through the fifth plane mirror 28 to form a light beam 18, and a small amount of 1064nm fundamental frequency light and 532nm double frequency light remaining in the output light are reflected by the fifth plane mirror 28 to form a light beam 17, thereby filtering out a small amount of 1064nm fundamental frequency light and 532nm double frequency light remaining in the output light.

[0051] like Figure 6As shown in the figure, when the optical axis directions of the frequency doubling crystal (located on the right) and the sum frequency crystal (located on the left) are consistent, based on the walk-off between the 1064nm fundamental frequency light and the 532nm frequency doubling light during the frequency doubling process, the walk-off will be further superimposed during the sum frequency process, resulting in a significant reduction in the overlapping area between the 532nm frequency doubling light and the 1064nm fundamental frequency light in the sum frequency crystal, thereby reducing the conversion efficiency of the sum frequency process.

[0052] When the optical axis directions of the frequency doubling crystal and the sum frequency crystal are inconsistent, the 1064nm fundamental frequency light and the 532nm frequency doubling light separated due to walk-off in the frequency doubling crystal will reunite after passing through the sum frequency crystal, making the overlapping area of ​​the two light beams in the sum frequency crystal larger, and finally a high-power 355nm ultraviolet laser output can be obtained. Figure 5 An example is shown, in which Figure 5 The y and z axes of the neutral frequency crystal are relative to Figure 6 The y and z axes of the sum frequency crystal are rotated 180°, thereby changing the direction of the optical axis of the sum frequency crystal, thereby bringing about the re-overlapping of the 1064nm fundamental frequency light and the 532nm double frequency light, achieving walk-off compensation, and thus improving the conversion efficiency of the sum frequency crystal.

[0053] Due to the existence of walk-off effect, the shape of the light beam during transmission in the crystal may be distorted or deformed, which is often called distortion, which will lead to poor beam quality. For intracavity 355nm ultraviolet laser, compared with walk-off superposition, walk-off compensation can achieve smaller beam distortion and diffusion, making the beam mode of 355nm ultraviolet laser more stable and the focusing performance better, thereby improving the beam quality of 355nm ultraviolet laser.

[0054] Preferably, the walk-off compensation optimum point is determined by adjusting the parameters of the sum frequency crystal, the frequency doubling conversion efficiency, the quality of the frequency doubling and fundamental frequency beams, etc. It can be understood that at the walk-off compensation optimum point, there is no walk-off overcompensation and the walk-off compensation effect is optimal.

[0055] In the prior art, in order to improve the conversion efficiency of the crystal, the radius of the fundamental mode spot at the nonlinear crystal is generally reduced, but this will increase the thermal effect of the nonlinear crystal, shorten the life of the nonlinear crystal, and reduce the beam quality of the intracavity harmonics during high-power operation. At the same time, under high-power pumping, the laser crystal has a strong thermal lens effect, and the nonlinear crystal also has a thermal lens effect.

[0056] Based on such considerations, in the present application, on the basis that walk-off compensation can improve the conversion efficiency of the sum frequency crystal, the intra-cavity structure can fully utilize the advantages of the high power density of the 1064nm fundamental frequency light in the cavity, ensure the high-power output of the 355nm ultraviolet laser, and at the same time, by adjusting the parameters of the resonant cavity 3 (for example, by adjusting the curvature combination of the first plano-convex mirror 14 and the second plano-convex mirror 15), the radius of the fundamental mode spot at the nonlinear crystal (for example, the sum frequency crystal) is greatly amplified, the thermal effect of the nonlinear crystal is effectively reduced, the life of the nonlinear crystal is extended, and at the same time, the beam quality of the intra-cavity harmonics during high-power operation is improved.

[0057] In the prior art, in order to extend the service life of the sum frequency crystal, one solution is to use LBO crystal cut at the Brewster angle as the nonlinear medium of the intracavity sum frequency process. However, the introduction of the Brewster angle will cause astigmatism in the fundamental frequency light, thereby affecting the output beam quality and conversion efficiency of the 355nm ultraviolet laser, and the overall optical path adjustment of the resonant cavity becomes complicated.

[0058] Based on such considerations, on the basis of the above, preferably, both the frequency doubling crystal and the sum frequency crystal are nonlinear crystals with double-ended vertical cuts. The double-sided vertical cuts avoid the fundamental frequency light astigmatism caused by the introduction of the Brewster angle. At the same time, by adjusting the parameters of the resonant cavity 3, the fundamental frequency light beam passing through the sum frequency crystal is made nearly parallel, compensating for the defect of low conversion efficiency caused by the larger fundamental frequency light spot, thereby further improving the sum frequency conversion efficiency.

[0059] Preferably, the all-solid-state 355nm laser further includes a convex lens 12 and a sixth plane mirror 11. The convex lens 12 is arranged outside the laser resonant cavity 3 and is located on the exit light path of the second plane convex mirror 15. The convex lens 12 is located between the second plane convex mirror 15 and the sixth plane mirror 11. The first plane convex mirror 14 and the second plane convex mirror 15 can reflect the 1064nm fundamental frequency light and transmit the 888nm pump light. The pump light that has passed through the gain medium 4 once but has not been absorbed is reflected by the sixth plane mirror 11 after passing through the convex lens 12, and then returned to the gain medium 4 again after being focused by the convex lens 12, thereby improving the light-to-light efficiency of the 888nm pump light-1064nm fundamental frequency light, providing more 1064nm fundamental frequency light for the nonlinear frequency conversion in the cavity, thereby ensuring a higher output power of the 355nm ultraviolet laser.

[0060] The present application utilizes the beam coupling system 2 to achieve good mode matching between the cavity mode and the pump mode at the gain crystal. The size of the cavity mode of the laser at the gain crystal can be controlled by optimizing the parameters of the resonant cavity 3 to ensure that the 1064nm fundamental frequency light is still TEM at high power output. 00 mold.

[0061] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A fully solid-state 355nm laser, characterized in that: It includes pump source, beam coupling system, laser resonant cavity and output system; The beam coupling system is arranged on the outgoing optical path of the pump source, the laser resonant cavity is arranged on the outgoing optical path of the beam coupling system, a gain medium and adjacently placed frequency doubling crystals and sum frequency crystals are arranged in the laser resonant cavity, and the output system is arranged on the outgoing optical path of the sum frequency crystal; Wherein, the optical axis direction of the frequency doubling crystal is inconsistent with the optical axis direction of the sum frequency crystal, so that the walk-off generated by the frequency doubling process is used to compensate for the walk-off generated by the sum frequency process; Among them, the phase matching angle of the frequency doubling crystal is θ=90°, Φ=(10.8°-11.6°); the phase matching angle of the sum frequency crystal is θ=(42.2°-43.4°), Φ=90°.

2. The all-solid-state 355nm laser according to claim 1, characterized in that: The frequency doubling crystal is a nonlinear crystal of type I critical phase matching mode, and the sum frequency crystal is a nonlinear crystal of type II critical phase matching mode.

3. The all-solid-state 355nm laser according to claim 1 or 2, characterized in that: The frequency doubling crystal and the sum frequency crystal are both nonlinear crystals with double-ended vertical cut surfaces.

4. The all-solid-state 355nm laser according to claim 1, characterized in that: The laser resonant cavity comprises a first plano-convex mirror, a second plano-convex mirror and a gain medium placed between the first plano-convex mirror and the second plano-convex mirror. The output light of the beam coupling system enters the laser resonant cavity through the first plano-convex mirror.

5. The all-solid-state 355nm laser according to claim 4, characterized in that: The laser resonant cavity also includes a first plane mirror and a second plane mirror, an acousto-optic Q-switch is provided on the optical path between the first plano-convex mirror and the first plane mirror, the frequency doubling crystal and the sum frequency crystal are arranged on the optical path between the second plano-convex mirror and the second plane mirror, and the frequency doubling crystal is closer to the second plane mirror than the sum frequency crystal.

6. The all-solid-state 355nm laser according to claim 5, characterized in that: The output system includes a third plane mirror and a fourth plane mirror. The third plane mirror is located on the main light path between the second plano-convex mirror and the sum frequency crystal and has an angle of 45° with the main light path. The fourth plane mirror is arranged outside the laser resonant cavity and is located on the reflected light path of the third plane mirror.

7. The all-solid-state 355nm laser according to claim 4, characterized in that: The laser resonant cavity also includes a first plano-concave mirror and a second plano-concave mirror, an acousto-optic Q-switch is provided on the optical path between the second plano-convex mirror and the first plano-concave mirror, a isolator is provided on the optical path between the first plano-convex mirror and the second plano-concave mirror, the frequency doubling crystal and the sum frequency crystal are arranged on the optical path between the first plano-convex mirror and the second plano-concave mirror, and the frequency doubling crystal is closer to the first plano-concave mirror than the sum frequency crystal.

8. The all-solid-state 355nm laser according to claim 7, characterized in that: The output system comprises a fifth plane mirror, which is arranged outside the laser resonance cavity and located on the output light path of the second plano-concave mirror.

9. The all-solid-state 355nm laser according to claim 5 or 7, characterized in that: It also includes a convex lens and a sixth plane mirror. The convex lens is arranged outside the laser resonance cavity and located on the output light path of the second plane-convex mirror. The convex lens is located between the second plane-convex mirror and the sixth plane mirror.

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