【作者】 李玉峰；

【导师】 王月珠；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2008， 博士

【摘要】 随着红外激光光源在激光遥感、激光测距、光谱分析、大气环境监测、空间通讯以及军事方面应用的不断扩展,其重要性越来越明显。Tm激光器的输出波长为2μm附近,处于大气窗口,为遥感探测以及光电对抗提供了有利工具,是相干多普勒测风雷达、差分吸收雷达和激光测距机等系统的理想光源。此外,Tm固体激光器还是获得3⁵μm波段光学参量振荡激光输出的理想泵浦源。本论文从理论和实验两个方面对常温下四种单掺Tm³⁺固体激光器进行了较为深入细致的比较研究和探索。首先对Tm³⁺在GdVO₄和YAP基质中红外、可见和紫外波段的吸收光谱、发射光谱和荧光寿命进行实验测量,给出了详细的能级分布和高度。其次,根据这些基本数据,计算出晶体的吸收截面、发射截面和有效受激发射截面。最后,与Tm³⁺在LuAG和YAG基质中的光谱性质比较,定性的分析了晶体基质对Tm³⁺能级分布和跃迁的影响。这些数据是J-O理论计算和激光器实验研究的基础。理论方面,主要是对Tm³⁺在不同基质中的光谱参数进行计算分析并建立了Tm激光器连续和Q运转的速率方程模型。首先,通过J-O理论,计算了Tm³⁺在GdVO₄和YAP中的强度参数并获得了多项光谱参数（自发辐射跃迁几率、辐射寿命、荧光分支比和积分发射截面）。通过对光谱参数的对比,从理论上分析了Tm³⁺在哪些晶体基质中和Tm³⁺的哪些跃迁最有可能获得激光输出,并对上转换荧光所发生的能级和强弱对比进行合理解释。其次,在详细地分析了粒子跃迁和能量传递过程的基础上,考虑了能量传递上转换和基态损耗效应的影响,建立了端面连续泵浦Tm激光器的准三能级速率方程的理论模型。得到了描述输出功率与泵浦功率关系的方程,利用此方程讨论了晶体长度、粒子掺杂浓度、输出镜透过率等对激光器输出特性的影响。并讨论了不同上能级寿命情况下,Q脉冲输出单脉冲能量与调制频率之间的关系,为Tm激光器的设计提供了理论基础。最后,在Tm激光器不同运转模式下,理论分析了F-P标准具、复合腔和双折射滤光片对波长选择和线宽压缩作用。此外,利用ANSYS软件不仅计算了Tm:GdVO₄和Tm:YAP晶体内的温度梯度分布而且对注入锁定实验中出现的试验平台共振频率进行了理论分析。实验方面,主要对不同基质的Tm激光器在单频、调谐、调Q等运转模式下的实验结果进行比较分析并进行优化设计,为不同应用方向的Tm激光晶体的选择提供重要的参考依据。首先对于单频输出的Tm:GdVO₄、Tm:YAP、Tm:YAG和Tm:LuAG微片激光器进行了详细的实验研究。分别利用标准具法和复合腔法获得了连续单频输出Tm激光器,并利用腔内插入双折射滤光片和标准具的方法实现了宽带可调谐的单频Tm:YAP激光输出。其次,研究在高功率泵浦条件下Tm:GdVO₄、Tm:YAP、Tm:YAG和Tm:LuAG块状晶体激光的连续波输出,连续波宽带调谐输出,声光调Q等输出性质,从不同角度给出影响连续功率输出的各种因素,包括:晶体材料、晶体质量、耦合输出透射率、晶体长度、工作温度等。分析了不同晶体材料的热力学性质、测量了热透镜焦距。给出Q输出条件下,泵浦功率和调制频率等因素对脉冲宽度的影响。最后通过对常温2微米种子光注入锁频激光器的初步实验探索,为以后进行的系统设计和搭建提出了优化方案。更多还原

【Abstract】 Widely applicable mid-infrared laser sources become more and more important in laser remote sensing, laser target detecting, spectra analysis, atmospheric environment monitoring, space communicating and special military applications. Emission wavelength of Tm laser system is near 2μm, just within atmospheric window, it provides an effective tool for remote sensing and photoelectric countermeasures. Tm laser is thought to be an ideal laser source for coherent Doppler lidar, differential absorption lidar （DIAL） and laser ranging and tracking system. In addition, Tm laser is an ideal pump sources for optical parameter oscillator （OPO） in the 3⁵μm band. This thesis investigates and explores four diode-end-pumped thulium-doped lasers theoretically and experimentally.As the basis of J-O theory calculation and Tm laser experiments, the absorption and emission spectrum of Tm:GdVO₄ and Tm:YAP in the infrared visible and ultraviolet band are measured, the distribution and lifetime of thulium energy levels are also given. According to experimental data, the absorb cross section, emission cross section and effective emission cross section are calculated. Compared with the spectra properties of Tm:LuAG and Tm:YAG, the distribution and transition of Tm³⁺ energy levels in different single crystals are discussed.In theoretical aspects, we mainly calculate the optical parameters of Tm³⁺ in different materials and build the end-pumped quasi-three-level mode of Tm laser system. First of all, according to the absorption and emission spectrum data, we calculate the intensity parameters of Tm³⁺ in GdVO₄ and YAP single crystals, and then the spectral parameters （Spontaneous emission transition rate, radiative lifetime, fluorescence branching ratio and integrated emission cross section） between the exited state and the lower state are given. The problem of which crystal and which level of Tm³⁺ is probable for laser emission is analyzed theoretically, the upconversion process and intensity detected in visible band are explained appropriately. Secondly, After getting the transition and energy transfer process of Tm³⁺ levels and considering the influence of upconversion and grand state dissipaton, we build the end-pumped quasi-three-level mode of Tm laser system. The equation between input power and output power is analyzed, the length of crystal, the concentration of Tm³⁺ and output coupler that contribute to the change of output power are given. The relationship between energy per q-switch pulse and modulate frequency are discussed with different uplevel lifetimes. At last, In different Tm laser operation modes, the frequency selective property and line width compression property of F-P etalon double-cavity and birefringence（BF） are analyzed. In addition, the temperature gradient of Tm:GdVO₄ and Tm:YAP crystal and the sympathetic vibration frequency of experimental platform are calculated by ANSYS software.In experimental aspects, we mainly make comparative study of Tm lasers in different operation modes such as single frequency, tunable, Q-switch and so on. All of these results supply the important reference data to how to selected Tm crystals in different application directions. First of all, single frequency Tm:GdVO₄, Tm:YAP,Tm:YAG and Tm:LuAG microchip lasers are proved and get detailed comparison. Single frequency Tm lasers are achieved by F-P etalon and double-cavity methods, widely tunable single frequency Tm:YAP laser with etalons and BF in the cavity is proved. Secondly, High power Tm:GdVO₄, Tm:YAP, Tm:YAG and Tm:LuAG lasers operating at continue-wave, widely tunable contimuewave and acousto-optic q-switch modes are compared and analyzed. The factors that affect output power such as crystal material, crystal quality, output coupler, crystal length and temperature control are also given. The thermal focal lengths of crystals are measured. In condition of q-swtich pulse output, the relationship among pump power, modulate frequency and pulse width is measured and discussed. Finally, a preliminary experiment of seed injected ring cavity Tm laser is proved and it gives reference data for the later laser system design and build.更多还原