| 题名 | 大气遥感及测风激光雷达单频全固态激光器技术研究 |
| 作者 | 谢小兵 |
| 文献子类 | 博士 |
| 导师 | 朱小磊 |
| 关键词 | 2μm激光器 2μm laser 非线性光学 nonlinear optics 紫外激光器 355nm ultraviolet laser 单频脉冲激光器 single frequency pulsed laser |
| 其他题名 | Research on technology of single frequency all solid state laser for atmospheric sensing and wind lidar |
| 英文摘要 | 本论文以大气CO2浓度探测差分吸收激光雷达和混合脉冲多普勒测风激光雷达的应用需求为背景，探索基于纳秒脉冲非线性频率变换技术实现单频脉冲激光输出的研究。重点开展了OPO技术产生单频2.05μm脉冲激光以及和频技术产生大能量355nm紫外激光的理论与实验研究。 本论文的主要工作和创新点包括： 介绍OPO的基本原理与相位匹配技术。采用平面波近似，模拟分析脉冲SRO的泵浦阈值与泵浦脉宽、腔长和耦合输出率关系，研究最佳泵浦脉宽及其影响因素。基于高斯光束高斯脉冲模型仿真了SRO转换效率与泵浦超阈度、耦合输出率、腔损耗的关系。研究纳秒脉冲SRO输出光束质量和光谱宽度的特点，提出改善OPO输出光束质量和压窄光谱宽度的可行方案。 开展了自由运转2.05μm纳秒脉冲SRO输出特性的实验研究。采用平平腔结构，设计并搭建1.06μm单频激光抽运的2.05μm KTP-SRO实验装置，重点研究不同KTP晶体长度、不同耦合输出率时OPO输出特性与转换效率变化规律。在400Hz重复频率下，获得了单脉冲能量为0.9mJ的2.05μm信号光输出，脉宽约3.7ns，对应泵浦光-信号光转换效率约为18%，光束质量因子M2优于3。在此基础上优化设计8字形行波稳定环形腔，开展环形腔2.05μm 脉冲KTP-SRO输出特性研究，获得了高斜率转换效率、基横模的2.05μm波长纳秒脉冲激光输出。在20Hz重复频率下，输入泵浦脉冲能量为11mJ时，获得2.4mJ的2.05μm信号光输出，脉宽约24ns，泵浦光-信号光转换效率达到22%，斜率效率达到53%，输出信号光脉冲能量稳定性约为1%。实验结果证实了稳定环形腔的限模特性与高效运转，为后续种子注入奠定基础。 优化设计并搭建1.06μm单频脉冲激光抽运的种子注入纳秒脉冲KTP-SRO实验系统，研究了种子注入前后脉冲SRO输出特性变化规律。在8字形稳定环形腔中，通过Ramp-Hold-Fire锁腔技术，利用种子注入OPO实现了单频窄线宽的2.05μm脉冲激光输出。在20Hz重复频率下，当抽运脉冲能量达到11.4mJ时，种子注入后SRO获得了单脉冲能量为2.6mJ的单频脉冲2.05μm信号光输出，对应泵浦光-信号光转换效率约为23%，脉宽约17.6ns，外差法实测信号光线宽约为26.5MHz，接近傅里叶变换极限，输出信号光光束质量因子M2值小于1.2。为进一步提升单频2.05μm脉冲激光输出能量以满足机载和星载激光雷达应用要求，设计了OPA放大系统提升2.05μm单频脉冲信号光能量。 在平面波近似下，考虑基波损耗与相位失配的模型，分析并模拟倍频效率与非线性驱动、相位失配量的变化关系，指出采用最佳泵浦光斑和最佳晶体长度是获得高效率倍频的关键。基于平面波近似和相位失配模型，仿真分析和频效率与基频光子数混合比、基频光强以及相位失配量的关系。对比研究了不同倍频晶体、和频晶体的特性。 采用双LBO晶体的外腔级联倍频与和频技术方案，以大能量单频1.06μm脉冲激光器为基频源，开展大能量355nm单频脉冲紫外激光器实验及其输出特性研究。使用重复频率为30Hz单脉冲能量为418mJ的基频激光倍频，实验实现最高单脉冲能量达到225mJ的532nm单频脉冲绿光输出，倍频效率达到54%，输出532nm激光光束质量因子M2约为2.5，脉宽约为10.8ns，和频后获得了脉冲能量为226mJ的单频355nm脉冲紫外激光输出，基频光-紫外光的和频转换效率达到55%，实测355nm紫外激光光束质量因子M2约为3.0，脉宽为12.2ns左右。为获取更高能量的单频355nm紫外激光，使用重复频率为100Hz单脉冲能量为772mJ的激光器作为基频源时，级联倍频和频后输出289mJ的355nm单频紫外脉冲激光。实验获得的大能量355nm单频紫外脉冲激光具备应用于星载直接测风多普勒激光雷达的潜力。; Based on the application requirements of atmospheric CO2 concentration detection differential absorption lidar and hybrid pulse Doppler wind lidar, the study of single frequency pulsed laser output by nanosecond pulse nonlinear frequency conversion technology is explored. This thesis focuses on the theoretical and experimental research of OPO technology to generate single-frequency 2.05μm pulsed laser and sum frequency technique to produce high-energy 355nm ultraviolet laser. The main contents and innovations of this thesis are as following: The basic principles of OPO and phase matching technology are introduced. Considering the plane wave approximation, the relationships between the pumping threshold of pulse SRO and the pump pulse width, cavity length and coupling output transmission are modeled, and the optimal pump pulse width and its influencing factors are discussed. The relationships between SRO conversion efficiency and pump scales over threshold, coupling output transmission and cavity loss are simulated based on Gaussian beam and Gaussian pulse model. The characteristics of the beam quality and spectral width of the nanosecond pulse SRO are analyzed, and several feasible schemes to improve the OPO output beam quality and compress the spectral width are proposed. An experimental study on the output characteristics of free running 2.05μm nanosecond pulse SRO is carried out. The experimental setup of 2.05μm KTP-SRO pumped by 1.06μm single-frequency laser is designed and fabricated based on the plane-parallel cavity. The output feature and conversion efficiency of OPO with different KTP crystal lengths and different coupling output transmissions are studied emphatically. At 400Hz pulse repetition frequency, a 2.05μm signal laser output with a single pulse energy of 0.9mJ is obtained. The pulse width is about 3.7ns, the corresponding conversion efficiency from the pump to signal is about 18%, and the beam quality factor M2 is better than 3. On this basis, a stable 8-shaped traveling wave ring cavity is designed and optimized, and the output characteristic of ring cavity 2.05μm pulsed KTP-SRO are studied. A fundamental transverse mode 2.05μm wavelength nanosecond pulse laser output with high slope conversion efficiency is obtained. At a repetition rate of 20 Hz, when the input pump pulse energy reaches 11 mJ, a 2.05 μm signal laser output of 2.4 mJ is achieved. The pulse width is around 24 ns, and the pump-to-signal conversion efficiency is about 22%, with the slope efficiency as high as 53%. The output signal laser pulse energy stability is measured to be about 1%. The experimental results confirm the feature of mode limiting and efficient operation of the stable ring cavity, which lays the foundation for the subsequent seed injection. The experimental system of injection-seeded nanosecond pulse KTP-SRO pumped by 1.06μm single-frequency pulsed laser is optimized. The difference of pulse SRO output characteristics before and after seed injection is studied. In the 8-shaped stable ring cavity, by use of the Ramp-Hold-Fire cavity-locking technology, a single-frequency narrow linewidth 2.05μm pulsed laser output from injection seeded OPO is demonstrated. At pulse repetition frequency of 20Hz, when the pumped pulse energy comes to 11.4mJ, a single frequency signal laser at 2.05μm with single pulse energy of 2.6mJ is obtained from injection seeded SRO. The corresponding conversion efficiency from pump-to-signal is about 23% with pulse width of about 17.6ns. The heterodyne measursing results shows that the signal laser linewidth is around 26.5MHz, close to the Fourier-transform-limit, and the output signal laser beam quality factor M2 is less than 1.2. In order to further increase the single frequency 2.05μm pulsed laser output energy to meet the requirements of airborne and spaceborne lidar applications, an OPA system is designed to boost the pulse energy of 2.05μm single-frequency pulsed signal laser. Under the plane wave approximation, considering the fundamental wave loss and phase mismatch model, the relationships between the frequency doubling efficiency and the nonlinear drive as well as the phase mismatch is analyzed, and it is pointed out that using the optimal pump spot and the optimum crystal length are key to obtain high frequency doubling efficiency. Based on plane wave approximation and phase mismatch model, the relationships between sum frequency efficiency and fundamental frequency photon number mixing ratio, fundamental frequency intensity and phase mismatch are simulated and discussed. The characteristics of different frequency doubling crystals and sum frequency crystals are compared. Based on the technical method of extra-cavity cascaded LBO crystals frequency doubling and sum frequency, the experiment and output characteristics of high energy 355nm single frequency pulsed ultraviolet laser are studied by use of high energy single-frequency 1.06μm pulsed laser as the base frequency source. The 532nm single-frequency pulse green light output with a maximum single pulse energy of 225mJ was achieved by adopting a fundamental frequency laser with repetition rate of 30Hz and pulse energy of 418mJ. The frequency doubling efficiency is 54% and the output 532nm laser beam quality factor M2 is measured to be about 2.5. The 532nm green laser pulse duration is about 10.8ns. The single-frequency 355nm pulsed ultraviolet laser output with pulse energy of 226mJ is obtained from the sum frequency crystal. The conversion efficiency from fundamental wave to the ultraviolet light is 55%, and the measured 355nm UV laser beam quality factor M2 is about 3.0 with pulse width of about 12.2ns. In order to obtain a higher energy single-frequency 355nm UV laser, a 100Hz 1064nm single-frequency laser with single pulse energy of 772mJ is used as the fundamental frequency source, and the cascaded frequency doubler and sum frequency module generates 289mJ 355nm single-frequency UV pulse laser. The high-energy 355nm single-frequency UV pulse laser obtained from the experiment has the potential to be applied in the spaceborne direct detection Doppler wind lidar. |
| 学科主题 | 光学工程 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/30927]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 谢小兵. 大气遥感及测风激光雷达单频全固态激光器技术研究[D]. |
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