| 题名 | 2μm固态单频脉冲激光器研究 |
| 作者 | 舒仕江 |
| 学位类别 | 博士 |
| 答辩日期 | 2011 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 陈卫标 |
| 关键词 | Tm,Ho:LuLF 全固态激光器 种子注入 声光调Q 速率方程 |
| 其他题名 | Research on 2μm Solid-State Single-Frequency Pulsed Laser |
| 中文摘要 | 相干多普勒测风激光雷达要求激光发射源人眼安全、单频、高脉冲能量、高效率和结构紧凑。2μm波段的固态激光器具有人眼安全和高的大气透过特性优势，同时可以兼顾结构紧凑的要求，成为相干探测激光雷达的重要候选光源。 论文首先对具有2μm波段发射谱的固体激光材料做了简要介绍，然后根据相干探测对2μm激光器提出的技术要求，确定采用Tm,Ho:LuLF晶体作为本激光系统的增益介质。接着论文回顾了国际上主要的2μm相干探测激光雷达发射光源的发展历史，为研制2μm固态单频脉冲激光器提供参考。 Tm,Ho:LuLF晶体的光谱学性质直接影响其激光器的性能，所以对其光谱学性质的了解是进行相关激光器设计和模拟的前提条件。论文第二章就Tm,Ho:LuLF晶体主要光谱学参数的含义以及相关获取技术的原理作了详细说明。通过对该材料准三能级特性的分析，揭示了其粒子数反转阈值与温度和激光发射波长的关系，解释了不同运转模式下激光器具有不同发射波长的现象。 论文第三章针对测风应用对2μm激光器提出的技术要求，制定了本系统的实现方案，并介绍相关的实验研究工作。整套系统采用种子注入主振荡功率放大（MOPA）的方案。单频种子源是一台连续运转的Tm,Ho:LuLF激光器，通过在谐振腔内插入双FP标准具实现单频运转和波长的粗略调谐。功率振荡器部分采用四镜“8”字环形腔结构，环形腔两路输出中的一路用于种子注入。为了获得大能量的脉冲输出，激光头采用LD侧面泵浦的结构，并通过声光Q开关实现调Q输出。由于Tm,Ho:LuLF激光介质的准三能级特性，激光器工作在较低的重复频率（5 Hz），并且通过水冷的方式将Tm,Ho:LuLF激光棒控制在较低的温度（水温10℃），以降低其出光阈值。为得到单频输出，系统采用 ramp-fire技术来实现功率振荡器谐振腔腔长与种子激光器频率的匹配。 多纵模运转时，振荡器最大静态输出脉冲能量为445 mJ，对应9.51%的光光效率, 平均斜率效率为18.2%；最大调Q输出脉冲能量为75.5 mJ，对应1.61%的光光效率, 平均斜率效率为2.56%。单程经过放大器后，对75.5 mJ的入射激光能量，得到了最大114 mJ的放大能量输出，对应1.51的放大倍率。单频运转时，振荡级输出调Q脉冲能量为69 mJ的，放大后达到105 mJ。 论文最后利用传输矩阵法计算了谐振腔内激光光束的传输特征参数，并通过一个速率方程模型在平顶光束与高斯光束两种情形下对激光器进行了数值模拟。模拟结果揭示了输出脉冲能量随泵浦脉冲能量变化的非线性关系，但模拟所得的脉冲建立时刻比实验结果要晚。 本论文对Tm,Ho:LuLF激光材料特性进行了理论归纳和实验验证，解释了激光发射波长随激光器操作条件而变化的现象，确立了相干多普勒激光雷达激光发射源的实验方案，完成了相关的实验研究，获得了2μm单频高能激光脉冲输出，并通过数值模拟揭示了该激光器的主要动力学特性。 |
| 英文摘要 | An eye-safe single-frequency high-energy compact laser is required as the transmitter of a coherent Doppler wind lidar system. 2μm solid-state lasers become the key candidate for their eye-safe wavelength range, high atmosphere transmittance, and small size. Solid-state laser material at the wavelength range of 2μm is introduced briefly at first. According to technical requirements for coherent wind lidar application, Tm,Ho:LuLF is selected as the laser medium in our system. The reference of development of 2μm solid-state laser transmitters is also reviewed in Chapter 1. Spectroscopic properties of Tm,Ho:LuLF influence its laser performance directly, and they are also the precondition for designing or simulating a laser. Meaning of these spectroscopic data and related principle of acquirement technologies are introduced in detail in Chapter 2. By analyzing the quasi-three-level properties of Tm,Ho:LuLF, the relationship between its population inversion threshold, temperature and lasing wavelength is revealed, and the phenomenon is explained that the lasing wavelength depends on the running condition. According to technical requirements for underdeveloping coherent wind lidar, an injection-seeded Master Oscillator Power Amplifier (MOPA) system is implemented in our experiment. The seed laser is consisted of a CW Tm,Ho:LuLF single frequency laser. The selection of single longitudinal mode and the tuning of wavelength are realized by two intra-cavity etalons. The master oscillator is configured with a figure-eight ring resonator. The seeder laser is injected into the master cavity through the output mirror. The pumping configuration of both oscillator and amplifier are three-direction side-pumped rod. An acousto-optic Q-switch is used. Due to the quasi-three-level properties of Tm,Ho:LuLF, the system is operated at a repetition rate of 5 Hz with water cooling. In order to obtain the single-frequency pulse output, ramp-fire technique is used to ensure the pulse laser cavity resonates with the seeder frequency. The oscillator outputs pulse energy 445 mJ and 75.5 mJ at free running and Q-Switched mode, respectively. It corresponds to an optical-optical efficiency of 9.51% and 1.61%, and an averaged slope efficiency of 18.2% and 2.56% , respectively. After single-pass amplification, the Q-switched output pulse energy of 114 mJ is achieved at the input pulse energy of 75.5 mJ with a gain of 1.51. With injection seeding, the oscillator Q-switched output pulse energy is 69 mJ, and 105 mJ is achieved after single-pass amplification. In the final chapter, Transfer Matrix Method is used to obtain the propagation parameters of the laser beam in the resonator. A rate equation model is used to simulate the laser by assuming the mode distribution is a top-hat beam or a Gaussian beam. Simulated results reveal the nonlinear relationship between output pulse energy and pump energy, but the simulated pulse build-up time is larger than the result of experiment. The main work of this dissertation is to design and develop the whole laser system. The results show that the 2μm single-frequency high-energy laser is available for the underdeveloping Doppler coherent lidar. Both simulation and experiment works will be the foundation for more high energy single frequency two micrometer laser. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15676]  |
| 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 | 舒仕江. 2μm固态单频脉冲激光器研究[D]. 中国科学院上海光学精密机械研究所. 2011. |
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