LD泵浦的高功率低噪声激光器研究
文献类型：学位论文
| 作者 | 冯滔 |
| 学位类别 | 博士 |
| 答辩日期 | 2013 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 朱健强 |
| 关键词 | 激光技术 非平面环形腔 光轴失谐 单频激光器 光轴变动 |
| 其他题名 | Study on Laser-Diode-Pumped High-Power Low-Noise Laser |
| 中文摘要 | 随着激光技术的发展，噪声和线宽指标变得越来越重要。高功率、低噪声的单频激光器以其光束质量好、相干长度长、谱线宽度窄和单色性好等优点，成为了现阶段激光器的发展目标。 单频技术的实现方案有很多，其核心是纵模选择：利用不同纵模之间的增益差异，只有位于中心频率附近、损耗最小的纵模能够实现振荡。在总结单频激光器设计理论基础上，通过分析各自的优缺点，本文中采用单块非平面环形腔结构实现单频激光的输出。 本文在已有研究的基础上，对非平面环形腔激光器的结构设计、腔内光轴失谐、激光晶体的热效应、激光器性能和腔内光轴变动等方面开展了系统的分析和研究，研究成果包括： 1、系统地分析了非平面环形腔的各个参数对激光器性能的影响。利用偏振态匹配理论建立了环路的琼斯矩阵方程，通过求解本征值数值分析了各个参数对腔内损耗及损耗差的影响。在此基础上，确定了非平面环形腔的结构参数和镀膜参数，完成了激光器的初步设计。 2、理论分析了腔内光轴失谐对光轴自洽的影响。针对在加工单块晶体过程中不可避免的加工误差，将单块晶体等效成四镜环形腔，将加工误差等效成反射镜的失调，建立了包含反射镜失调参数的光路矩阵方程。通过求解方程分别研究了距离误差和角度误差对光轴自洽的影响，并对单块晶体的前端面分别为平面和曲面两种情况进行了分析。结论表明，距离误差和前端面为曲面的设计不会影响光轴的自洽特征；针对前端面为平面的设计会导致光轴不能实现自洽的情况，从对称性和变化性两个方面分别分析了如何降低光轴失谐。在这些理论的指导下，成功完成了单块晶体的加工和检测，并积累了一套实用的加工工艺和检测方法。此研究为实现激光器的正常运转解决了先决条件。 3、分析了激光器运转时激光晶体的热效应。建立了非平面环形腔激光器中单块晶体的热力学模型，通过差分方法计算求解，得到了晶体内部的温度分布、端面形变分布、热致光程差分布以及理论热焦距随泵浦功率变化的规律。所得结论为激光器运转过程中的散热提供了理论依据的同时，也对激光器的输出特征进行了预估。 4、在以上理论分析的基础上，搭建了实验平台，并完成了激光器基本性能的测试。利用加工和镀膜的单块晶体，设计并搭建了LD抽运非平面环形腔激光器的实验平台，成功地实现了单频基横模的激光输出，获得了1.25W的功率输出。在1小时测试时间内的功率稳定性为±0.8%。两方向的光束质量M2分别为1.16和1.05，激光器的线宽小于2kHz。通过温度调谐实现了18GHz的频率调谐范围。利用光纤延迟自拍法对激光器频率的短期稳定度进行了理论分析与研究测试，结果表明激光器在100ms积分时间内的频率稳定度为4.7×10-12。 5、理论分析并验证了非平面环形腔中的光轴变动。基于较大功率输出过程中的高阶模情况，提出了稳光轴激光器的概念；并利用光轴变动理论，分析了光轴变动与泵浦功率的变化规律，以及腔结构参数对光轴变动的影响，为设计光轴变动较小的激光器提供了理论基础。实验结果表明，通过克服光轴变动能够保持激光器的基横模运转，并且能够进一步增大输出功率，从另一个角度为激光器性能的优化提供了思路。 |
| 英文摘要 | With the development of laser technology, the characteristics, such as noise and line width, become more important. The single-frequency laser with high power and low noise is the development goal because of the good beam quality, long coherence length, narrow line width, and better monochromaticity. The key of single-frequency technology is the longitudinal-mode selection. The longitudinal mode with the minimum loss near the center frequency can get oscillating through the gain difference between different longitudinal modes. By summarizing and comparing the implementation approaches of single-frequency lasers, a monolithic nonplanar ring oscillator is used to achieve the single-frequency laser in our study. Based on the reported researches, this dissertation mainly focus on the structural design of the nonplanar ring oscillator, discussions of optical-axis perturbations, analysis of thermal effects, measurements of laser properties, and studies of optical-axis variations. The results are summarized as follows. 1. The influences of the parameters of the non-planar ring oscillator on the laser properties were analyzed systematically. Through the eigenvalue calculation of Jones matrix equation established by the polarization matching, the influences of parameters on the intracavity loss and loss difference were analyzed. Therefore, the structure and coating parameters of the nonplanar ring oscillator would be determined, which accomplish the preliminary design of lasers. 2. The impacts of the optical-axis perturbations on the self-consistence of the optical axis were analyzed theoretically. Considering the inevitable manufacturing errors of the monolithic crystal, a four-equal-sided nonplanar ring resonator was chosen, and the manufacturing errors were equivalent to the mirror misalignments. Then the matrix equation was established including the misalignment parameters of mirrors. By solving the equation, the effects of the distance deviation and angle errors on the optical-axis self-consistence were discussed in the case of the plane and spherical front-end surfaces, respectively. The results indicated that the distance deviation and the design with spherical surface would not affect the characteristics of the optical-axis self-consistence. Conversely, using the design with the plane surface, the optical-axis self-consistence cannot be realized. The method for decreasing the optical-axis perturbation was analyzed from the aspects of symmetry and variability. According to those theories, we successfully fabricated and detected the monolithic crystal. This research solved the prerequisites for achieving the laser normal operation. 3. Thermal effects of the monolithic crystal during laser operations were analyzed. The thermodynamic model in the nonplanar ring oscillator laser was established. With the difference solution method, the distributions of temperature, end-surface deformation and thermo-induced optical-path difference were obtained. Based on the former calculations, the focal length of the laser crystal was also obtained. The results offered a theoretical guide for the heat dissipation and the estimation of laser output. 4. The laser experimental platform was built and the laser properties were measured based on the above theoretical analyses. The fabricated and coated monolithic crystal was used in LD-pumped non-planar ring oscillator laser. The output laser power with a single-frequency and a fundamental transverse mode was 1.25 W. The power stability of ±0.8% was obtained during the test time of 1 hour. The beam qualities M2 along two directions were 1.16 and 1.05, respectively. The line width of the laser output was less than 2 kHz. The frequency tuning range was 18 GHz by adjusting the temperature of the crystal. In addition, the short-term stability of laser frequency was obtained in theory and experiment by the self-beat-frequency method. The results showed that the short-term frequency stability was 4.7×10-12 within the integral time of 100 ms. 5. The optical-axis variations in the NPRO laser were analyzed in theory and verified in experiment. Based on the observation of high-order transverse modes in the cases of higher power outputs, the concept of the stable-optical-axis laser was proposed. Based on the optical-axis variations theory, the influences of the pump power and structural parameters on the optical-axis variations were analyzed to guide the design of the stable-optical-axis laser. The results showed that by overcoming the optical-axis variations the fundamental-transverse-mode operation was realized again and the output power increased. Therefore, the research was very helpful for the optimization of laser properties. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15766]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 冯滔. LD泵浦的高功率低噪声激光器研究[D]. 中国科学院上海光学精密机械研究所. 2013. |
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来源：上海光学精密机械研究所
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