【作者】 吴春婷；

【导师】 鞠有伦；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2011， 博士

【摘要】 2μm固体激光器具有人眼安全、大气消光比低、体积小等优点,使其成为相干多普勒测风激光雷达和差分吸收激光雷达的首选光源。注入锁频技术在固体激光器中的应用,使输出激光脉冲同时具备单纵模、窄线宽、高频率稳定度、足够单脉冲能量和脉冲宽度的特点,满足相干多普勒测风激光雷达对激光光源的要求。注入锁频激光器由主激光器、从激光器和注入锁频伺服系统三部分组成。本文对单掺Tm³⁺注入锁频固体激光器进行了理论分析和实验研究。理论方面,利用Tm³⁺激光介质的能级跃迁结构以及粒子的玻尔兹曼分布,建立了Tm³⁺激光器的准三能级速率方程理论模型,结合连续运转速率方程的求解,讨论了掺杂粒子浓度对输出激光性能的影响,计算了激光介质的最佳长度和掺杂浓度,并在此基础上求得了最佳谐振腔输出镜透过率。同时模拟了连续和长脉冲泵浦下激光器的弛豫振荡频率,结果表明Tm:YAG晶体更适合重复频率千赫兹以下的调Q。结合脉冲泵浦调Q速率方程理论模型,讨论了从激光器的脉冲建立时间,输出脉冲宽度、能量提取效率等问题。通过注入锁频的经典理论模型分析,对注入场、噪声场和锁定带宽方程进行了分析和求解,揭示了注入锁频的物理实质。并数值求解了注入锁频的时间特性,计算了实现锁频的最小注入功率。讨论了注入光强与注入锁频激光器的最大频率失谐量的关系。分析了注入锁频信号提取的影响因素,当主、从激光器的横、纵向模式匹配时,可以实现有效锁频信号的提取。实验方面,首先测量了Tm:YAG和Tm:LuAG两种激光介质的吸收谱、荧光谱及荧光寿命,对本文实验研究中激光介质和泵浦波长的选择及实验现象的分析提供了依据,同时为粒子能级跃迁的分析提供了前提。主激光器方面,利用F-P标准具法实现了主激光器的稳定、可调谐单纵模激光输出,并在此基础上进行了改进实验,提高了输出单纵模功率,实现种子光的线偏振激光输出。从激光器方面,从增加脉冲宽度、提高单脉冲能量和改善光束质量三个方面,对从激光器进行了理论和实验两个方面的研究。讨论了脉冲泵浦下激光介质的热效应问题,同时实验测得了脉冲泵浦下Tm:YAG的热焦距,然后利用ABCD环绕矩阵,优化“8”字环形从激光器的设计,使谐振腔可以适应更大范围内的热透镜焦距变化,保持稳定运转。从实验上获得了单脉冲能量、脉冲宽度、光束质量均满足测风雷达光源需要的Tm:YAG和Tm:LuAG从激光器调Q激光输出。在实验上设计并实现了主、从激光器之间的横、纵向模式匹配,完成了有效注入锁频信号的提取。最后,进行了单掺Tm³⁺注入锁频激光器的实验研究。讨论了锁频激光器输出特性的变化,测量了激光器的输出线宽,分析了失谐量、注入功率及调Q触发时间对锁频激光输出性能的影响。最终实现了重复频率15Hz、单脉冲能量2mJ、脉冲宽度356.2ns的Tm:YAG锁频激光输出,重复频率100Hz、单脉冲能量2.4mJ、脉冲宽度347.7ns的键合Tm:YAG锁频激光输出,以及重复频率50Hz、单脉冲能量1.8mJ、脉冲宽度293ns的Tm:LuAG锁频激光输出。更多还原

【Abstract】 2μm solid-state laser has been an important choice for the light source of Coherent Doppler Lidar and Differential Absorption Lidar, due to their characteristics of eye-safe, low atmospheric extinction ratio, small size and so on. With the application of injection locking technology to solid-state laser, the laser can be operated with single longitudinal mode（SLM）, narrow linewidth, high frequency stability, sufficient pulse energy and long pulse width output simultaneously, which could meet the requirements for lidar system. Injection locked laser contains master laser, slave laser and servo system. View of this condition and background, this dissertation intends to make efforts on the research of Tm³⁺-doped injection locked solid-state laser theoretically and experimentally, and hopefully we can make some contribution on the development and the application of pulsed SLM 2μm solid-state lasers.In theory, the Tm³⁺-doped quasi-three-level rate equation is established using the transition energy level structure of Tm³⁺ laser medium and the Boltzmann distribution of particles. Based on the continuous wave operation rate equation, optimum length and doping concentration of the laser medium and the best cavity output mirror transmissivity are calculated, and the effect of doping concentration of particles to the laser output performance is discussed. The laser relaxation oscillation frequency is also calculated under continuous and long pulse pumping. The results show that Tm:YAG crystal is more suitable for Q-switched operation under kHz repetition rate. According to the Q-switched operation rate equation using pulsed laser-diode（LD） pumping, the build-up time of laser pulse, the output pulse width and the energy extraction efficiency are discussed. Using the classical theory model of injection locking, injection field, noise field and locking bandwidth are analyzed. The minimum injection locking power is calculated. The relationship between the injected laser intensity and the maximum detuning frequency of the injection locking laser is discussed. The disadvantageous factors for extracted signal about injection locking are analyzed. Good matches between horizontal mode and vertical mode are helpful to achieve extracted locking signal effectively and to avoid the generation of false signals.In experiment, the absorption spectra, fluoresce spectra and fluorescence lifetime of Tm:YAG and Tm:LuAG are measured. That is helpful to select the laser medium and pump source, to explain the experimental phenomena and to provide a premise analysis for the particle level transition. For the master laser, by inserting two F-P etalons to the cavity, stable, single longitudinal mode and tunable laser output was realized. Furthermore, experiments are carried out to improve the output power of SLM linear-polarized laser laser. For the slave laser, the output laser characteristics are optimized, such as pulse width, pulse energy and the beam quality. The thermal effect of the pulsed LD pumping laser is discussed. The thermal focal length of Tm: YAG laser is measured experimentally. Then,‘8’ring laser cavity is designed and optimized by using the ABCD matrix theory, which is thermal insensitive, and it can be adapted to a wide change of thermal focal length and operated stably. After optimization, the single pulse energy, pulse width and beam quality of the Tm:YAG and Tm:LuAG slave laser can meet the requirements. Besides master laser and slave laser, the extract of the injection locking signal is an important part. Injection locking signal extraction is directly infected by the mode matching between the master laser and the slave laser. The matching of transverse mode and longitudinal mode were designed. And effective injection locking signal was extracted in experiment. Finally, Tm³⁺-doped injection locked lasers are achieved experimentally. The characteristics of the injection locking laser are discussed. The linewidth of the laser is measured. The influence of the detuning, the injected power and the trigger time of the Q-switch to the injection locking laser are analyzed. As a result, the single pulse energy of 2mJ and pulse width of 356.2ns for Tm:YAG injection locked laser is obtained at a repetition rate of 15Hz. Using a composite Tm:YAG laser crystal, the single pulse energy of 2.4mJ and pulse width of 347.7ns pulsed SLM laser is achieved at 100Hz. In addition, the single pulse energy of 1.8mJ Tm:LuAG injection locked laser is realized at 50Hz, with the pulse width of 293ns.更多还原