高功率全固态单频激光器的实验研究
发布时间：2018-08-14 16:38
【摘要】：高功率全固态单频绿光激光器具有结构紧凑、光束质量好、强度噪声低等优点,已经广泛应用于量子通信、全息成像、干涉测量等领域,还可通过倍频产生深紫外光以及作为高功率钛宝石激光器和OPO的泵浦源。但在进一步提升高功率单频绿光激光器的输出功率的过程中,我们遇到了如下问题：1)当进一步增大泵浦功率以提升激光器的输出功率时,激光器的输出功率不但没有上升,反而会下降,同时激光光束会由单横模退化为多横模；2)激光器在升降泵浦功率的过程中存在类双稳现象,同时伴随着输出功率的突升突降,导致腔内器件产生严重的热致应力突变进而影响激光器的使用寿命。经过研究,我们发现在高功率内腔倍频单频激光器中,不但增益晶体的热透镜效应对激光器性能有重要影响,而且光学单向器中的TGG晶体通过吸收腔内基频光产生的热透镜效应同样会严重影响激光器的工作状态。本文的研究主要是围绕TGG晶体的热透镜效应对激光器工作状态的影响以及如何缓解和补偿TGG晶体的热透镜效应展开的,另外我们还在考虑TGG晶体热透镜效应的基础上,研究了腔镜曲率半径对激光器工作状态的影响。我们首先利用ABCD矩阵分析了TGG晶体的热透镜效应对激光器工作状态的影响,然后进行实验验证。实验证明TGG晶体的热透镜效应不但存在,而且对激光器的工作状态有显著影响：使稳区变窄,降低最佳工作点对应的泵浦功率,最终限制激光器的输出功率。根据理论计算,我们可以通过缩短腔长去缓解TGG晶体热透镜效应的影响,提升激光器最佳工作点对应的泵浦功率进而提升输出功率,我们的实验结果和理论预期比较一致。但缩短腔长并不能消除TGG晶体热透镜效应的影响,因此在改变泵浦功率的过程中观察到激光器存在明显的类双稳现象,同时伴随着输出功率的突升突降。我们对类双稳现象进行了定性分析,进一步证明TGG晶体的热透镜效应源于TGG晶体对腔内基频光的吸收,而不是对泵浦光的吸收,这和增益晶体的热透镜效应的产生机制是不同的。在分析了TGG晶体对激光器工作状态的影响的基础上,我们选择具有负热光系数的单轴晶体——DKDP晶体,对TGG晶体的热透镜效应进行自适应性的动态补偿。首先我们确定了DKDP晶体薄片的切割方向,即光轴和通光方向的夹角为30°,以使DKDP晶体薄片的热透镜效应尽可能的各向同性,以有效补偿TGG晶体的热透镜效应。然后在固定的腔长下,利用三片厚度不同的DKDP薄片分别对TGG晶体的热透镜效应进行补偿,根据激光器最佳工作点对应的泵浦功率的变化,我们拟合得到了DKDP晶体薄片的热透镜焦距公式。由此我们计算得到,在当前的实验条件下,厚度为1.65 mm的DKDP薄片可以完全补偿8 mm长的TGG晶体的热透镜效应,因此我们利用现有的1.6 mm的补偿片进行调试。通过补偿,不但完全消除了激光器之前存在的类双稳现象,获得极为平缓的输出功率曲线,而且可将单频532 nm激光的最大输出功率从14.7 W提升至30.2 W。最后,针对早前文献中关于高功率固体激光器应该使用凸面腔镜取代平面腔镜以缓解增益晶体热透镜效应从而提升激光器输出功率的结论,我们首先进行了理论分析,发现当腔长固定时,随着腔镜曲率半径的增大,激光器的阈值泵浦功率和最佳工作点对应的泵浦功率均降低；而如果在增大腔镜曲率半径的同时对腔长进行适当调节,激光器也能获得和采用曲率半径较小的腔镜时类似的工作状态。然后我们选择一组平面腔镜和两组曲率半径分别为1500 mm和3000 mm的凸面腔镜分别在腔长固定和腔长可变的条件下进行实验,实验结果和理论预期比较吻合。我们还计算了不同腔镜曲率半径下的激光器的最佳腔长,可为采用类似腔型的高功率单频激光器的设计提供一定的理论指导。最后,我们采用平面腔镜进行调试,获得最高输出功率为12.97 W的单频532 nm激光器。创新性工作：1.研究了TGG晶体的热透镜效应对高功率单频激光器工作状态的影响,并通过缩短腔长去被动适应这种影响以提升激光器的输出功率。对激光器的类双稳现象进行了定性分析,进一步证明TGG晶体的热透镜效应源于TGG晶体对腔内基频光的吸收；2.在高功率单频激光器中利用DKDP晶体薄片对TGG晶体的热透镜效应进行动态补偿,获得30.2 W的全固态连续光内腔倍频单频532 nm激光器,据我们所知,这是目前同类型单频532 nm激光器所获得的最高的输出功率；3.研究了腔长和腔镜曲率半径的关系,指出先前文献中关于高功率固体激光器应当采用凸面腔镜以缓解增益晶体热透镜效应这一结论的局限性,证明即使采用平面腔镜,只要将腔长调整到适当长度,激光器也能获得和采用曲率半径较小的凸面腔镜时类似的工作状态。
[Abstract]:High-power all-solid-state single-frequency green laser has the advantages of compact structure, good beam quality and low intensity noise. It has been widely used in quantum communication, holographic imaging, interferometry and other fields. It can also generate deep ultraviolet light by frequency doubling and be used as the pump source of high-power Ti:sapphire laser and OPO. In the process of green laser output power, we encounter the following problems: 1) when the pump power is further increased to enhance the output power of the laser, the output power of the laser will not increase, but will decline, and the laser beam will degenerate from a single transverse mode to a multi-transverse mode; 2) in the process of raising and lowering the pump power of the laser. In high power intracavity frequency doubled single frequency lasers, not only the thermal lens effect of the gain crystal has an important effect on the performance of the lasers, but also the thermal lens effect of the gain crystal is found. The thermal lensing effect produced by TGG crystal in the optical unidirectional device through the fundamental frequency light in the absorption cavity will also seriously affect the working state of the laser. This paper mainly focuses on the influence of the thermal lensing effect of TGG crystal on the working state of the laser and how to mitigate and compensate the thermal lensing effect of TGG crystal. Considering the thermal lens effect of TGG crystal, the effect of the radius of curvature of the cavity mirror on the laser operating state is studied. First, the influence of the thermal lens effect of TGG crystal on the laser operating state is analyzed by ABCD matrix, and then verified by experiment. The experimental results show that the thermal lens effect of TGG crystal not only exists, but also affects the laser. According to the theoretical calculation, we can reduce the cavity length to alleviate the influence of the thermal lens effect of TGG crystal, increase the pump power corresponding to the optimal operating point of the laser, and then increase the output power. Our experimental results are in good agreement with the theoretical expectations. However, shortening the cavity length can not eliminate the thermal lens effect of TGG crystal. Therefore, the obvious bistability phenomenon is observed in the process of changing the pump power, accompanied by the sudden rise and fall of the output power. It is proved that the thermal lens effect of TGG crystal originates from the absorption of the fundamental frequency light in the cavity rather than the pump light, which is different from the thermal lens effect of gain crystal. Firstly, we determine the cutting direction of the DKDP crystal sheet, that is, the angle between the optical axis and the optical direction is 30 degrees, so that the thermal lens effect of the DKDP crystal sheet is as isotropic as possible to compensate the thermal lens effect of the TGG crystal effectively. Three DKDP sheets with different thickness are used to compensate the thermal lens effect of TGG crystal. According to the change of the pump power corresponding to the optimum operating point of the laser, we fit the thermal lens focal length formula of DKDP crystal sheet. From this, we calculate that the DKDP sheet with a thickness of 1.65 mm can be used under the current experimental conditions. The thermal lens effect of 8 mm long TGG crystal is completely compensated, so we use the existing 1.6 mm compensator to debug. By compensating, not only the bistability phenomenon existing before the laser is eliminated completely, but also the output power curve is very gentle, and the maximum output power of 532 nm single frequency laser can be increased from 14.7 W to 30.2 W. Finally, in view of the conclusion that convex mirrors should be used to replace planar mirrors in high-power solid-state lasers to mitigate the thermal lens effect of gain crystals and enhance the output power of lasers in previous literatures, we first made theoretical analysis and found that when the cavity length is fixed, the threshold pumping power of lasers increases with the increase of the curvature radius of cavity mirrors. The pump power corresponding to the rate and the optimum operating point decreases, and if the radius of curvature of the cavity mirror is increased and the length of the cavity is adjusted properly, the laser can achieve the same working state as that of the cavity mirror with a smaller radius of curvature. The experimental results are in good agreement with the theoretical expectation. The optimum cavity lengths of lasers with different radius of curvature are calculated, which can provide some theoretical guidance for the design of high power single frequency lasers with similar cavities. The mirror is debugged to obtain a single frequency 532 nm laser with a maximum output power of 12.97 W. Innovative work: 1. The influence of the thermal lens effect of TGG crystal on the working state of the high power single frequency laser is studied, and the output power of the laser is enhanced by reducing the cavity length to passively adapt to this effect. Qualitative analysis further proves that the thermal lens effect of TGG crystal originates from the absorption of fundamental frequency light by TGG crystal. 2. The thermal lens effect of TGG crystal is dynamically compensated by DKDP crystal sheet in high power single frequency laser, and a 30.2 W all-solid-state CW intracavity frequency doubling 532 nm laser is obtained. 3. The relationship between cavity length and the radius of curvature of cavity mirror is studied. It is pointed out that convex cavity mirror should be used to alleviate the thermal lens effect of gain crystal in high power solid-state lasers. It is proved that the cavity length should be kept as long as the plane cavity mirror is used. By adjusting the laser length to a suitable length, the laser can operate in a similar manner to the convex cavity mirror with a smaller radius of curvature.
【学位授予单位】：山西大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN248
[Abstract]:High-power all-solid-state single-frequency green laser has the advantages of compact structure, good beam quality and low intensity noise. It has been widely used in quantum communication, holographic imaging, interferometry and other fields. It can also generate deep ultraviolet light by frequency doubling and be used as the pump source of high-power Ti:sapphire laser and OPO. In the process of green laser output power, we encounter the following problems: 1) when the pump power is further increased to enhance the output power of the laser, the output power of the laser will not increase, but will decline, and the laser beam will degenerate from a single transverse mode to a multi-transverse mode; 2) in the process of raising and lowering the pump power of the laser. In high power intracavity frequency doubled single frequency lasers, not only the thermal lens effect of the gain crystal has an important effect on the performance of the lasers, but also the thermal lens effect of the gain crystal is found. The thermal lensing effect produced by TGG crystal in the optical unidirectional device through the fundamental frequency light in the absorption cavity will also seriously affect the working state of the laser. This paper mainly focuses on the influence of the thermal lensing effect of TGG crystal on the working state of the laser and how to mitigate and compensate the thermal lensing effect of TGG crystal. Considering the thermal lens effect of TGG crystal, the effect of the radius of curvature of the cavity mirror on the laser operating state is studied. First, the influence of the thermal lens effect of TGG crystal on the laser operating state is analyzed by ABCD matrix, and then verified by experiment. The experimental results show that the thermal lens effect of TGG crystal not only exists, but also affects the laser. According to the theoretical calculation, we can reduce the cavity length to alleviate the influence of the thermal lens effect of TGG crystal, increase the pump power corresponding to the optimal operating point of the laser, and then increase the output power. Our experimental results are in good agreement with the theoretical expectations. However, shortening the cavity length can not eliminate the thermal lens effect of TGG crystal. Therefore, the obvious bistability phenomenon is observed in the process of changing the pump power, accompanied by the sudden rise and fall of the output power. It is proved that the thermal lens effect of TGG crystal originates from the absorption of the fundamental frequency light in the cavity rather than the pump light, which is different from the thermal lens effect of gain crystal. Firstly, we determine the cutting direction of the DKDP crystal sheet, that is, the angle between the optical axis and the optical direction is 30 degrees, so that the thermal lens effect of the DKDP crystal sheet is as isotropic as possible to compensate the thermal lens effect of the TGG crystal effectively. Three DKDP sheets with different thickness are used to compensate the thermal lens effect of TGG crystal. According to the change of the pump power corresponding to the optimum operating point of the laser, we fit the thermal lens focal length formula of DKDP crystal sheet. From this, we calculate that the DKDP sheet with a thickness of 1.65 mm can be used under the current experimental conditions. The thermal lens effect of 8 mm long TGG crystal is completely compensated, so we use the existing 1.6 mm compensator to debug. By compensating, not only the bistability phenomenon existing before the laser is eliminated completely, but also the output power curve is very gentle, and the maximum output power of 532 nm single frequency laser can be increased from 14.7 W to 30.2 W. Finally, in view of the conclusion that convex mirrors should be used to replace planar mirrors in high-power solid-state lasers to mitigate the thermal lens effect of gain crystals and enhance the output power of lasers in previous literatures, we first made theoretical analysis and found that when the cavity length is fixed, the threshold pumping power of lasers increases with the increase of the curvature radius of cavity mirrors. The pump power corresponding to the rate and the optimum operating point decreases, and if the radius of curvature of the cavity mirror is increased and the length of the cavity is adjusted properly, the laser can achieve the same working state as that of the cavity mirror with a smaller radius of curvature. The experimental results are in good agreement with the theoretical expectation. The optimum cavity lengths of lasers with different radius of curvature are calculated, which can provide some theoretical guidance for the design of high power single frequency lasers with similar cavities. The mirror is debugged to obtain a single frequency 532 nm laser with a maximum output power of 12.97 W. Innovative work: 1. The influence of the thermal lens effect of TGG crystal on the working state of the high power single frequency laser is studied, and the output power of the laser is enhanced by reducing the cavity length to passively adapt to this effect. Qualitative analysis further proves that the thermal lens effect of TGG crystal originates from the absorption of fundamental frequency light by TGG crystal. 2. The thermal lens effect of TGG crystal is dynamically compensated by DKDP crystal sheet in high power single frequency laser, and a 30.2 W all-solid-state CW intracavity frequency doubling 532 nm laser is obtained. 3. The relationship between cavity length and the radius of curvature of cavity mirror is studied. It is pointed out that convex cavity mirror should be used to alleviate the thermal lens effect of gain crystal in high power solid-state lasers. It is proved that the cavity length should be kept as long as the plane cavity mirror is used. By adjusting the laser length to a suitable length, the laser can operate in a similar manner to the convex cavity mirror with a smaller radius of curvature.
【学位授予单位】：山西大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN248
【参考文献】
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1 王W毻，
本文编号：2183471
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