【作者】 王天衡；

【导师】 鞠有伦；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2009， 硕士

【摘要】 2μm激光器的输出波长为大气窗口,可应用于激光雷达、激光医疗、激光测距、光电对抗等领域。同时,2μm激光可以作为光学参量振荡器和光学参量放大器的泵浦源,从而实现3~5μm和8~12μm激光输出。单掺Ho激光器是常温条件下高性能的2μm相干光源,而发射波长在1.91μm的Tm:YLF激光器是单掺Ho激光器的理想泵浦源。本论文的主要工作是理论结合实验对采用体光栅作为腔镜的Tm:YLF激光器进行研究,从而获得窄线宽的1.91μm激光。理论方面,首先分析了Tm激光器运转机制并建立了速率方程,分析了Tm系统的上转换、再吸收以及基态损耗等效应对激光晶体特性的影响。其次,介绍了体光栅的基本原理及材料特性。对体光栅的衍射理论进行分析,并给出了体光栅衍射效率及反射带宽度的表达式,通过数值模拟分析了反射式体光栅厚度及折射率调制对衍射效率的影响,并采用分光光度计测量了反射式体光栅的透射光谱。此外,从泵浦源、工作物质、谐振腔三个方面对Tm:YLF激光器进行设计,并讨论了热透镜效应对谐振腔稳定性及模式匹配的影响。实验方面,首先利用体光栅作为Tm:YLF激光器的腔镜,获得了输出功率6.02W、峰值半高宽0.3nm的1.91μm激光输出,并比较分析了分别使用体光栅和传统腔镜时激光器的输出特性。其次,通过实验分析了泵浦波长、激光晶体温度、输出镜透过率、腔长等因素对激光器输出特性的影响。再次,通过实验的改进,采用镀膜的体光栅,实现了10.0W的稳定波长的1.91μm激光输出,相应的光光转换效率为32.1%,斜率效率为39.8%,输出线宽为0.1nm,激光光束质量M2因子为1.54。用获得的1.91μm激光泵浦Ho:YAP晶体,实现了2118nm连续激光输出。此外,测量并分析了热效应对体光栅波长选择性的影响,体光栅吸收热量温度升高后,激光器的输出波长红移。最后,根据理论及实验分析,提出了窄线宽、高功率、稳定输出的Tm:YLF激光器的设计方案。更多还原

【Abstract】 Atmosphere-window 2-μm laser has potential applications in many fields, such as laser radar, medical diagnoses and therapy, laser target detecting and photoelectric countermeasure. Furthermore, 2-μm lasers are effective pump sources for optical parametric oscillators and optical parametric amplifications, which can realize 3~5μm and 8~12μm laser output. Ho-doped laser is a good kind of coherent light source at room temperature, and 1.91-μm Tm:YLF laser is an effect pump source for Ho-doped laser. In this paper, we investigate both theoretically and experimentally in the field of Tm:YLF laser with a volume Bragg grating (VBG) as a resonator, so that narrow linewidth 1.91-μm laser can be obtained.Theoretically, the energy processes and rate equations of Tm lasers are analyzed at first, and the up-conversion effect, resorption and ground-state depletion effects of laser cystal are analyzed. Secondly, the fundamental and material properties of VBG are introduced. The expression of diffraction efficiency and linewidth of reflection zone are given according to the diffraction theory of VBG, and by numerical simulation, the impact of thickness and refractive index modulation on diffraction efficiency are discussed. In addition, the transmission spectrum of reflecting VBG is measured by spectrophotometer. Thirdly, Tm:YLF laser is designed in the field of pump source, gain medium and resonator. The resonator stability and the mode coupling are investigated, which are influenced by thermal focal effect.Experimentally, first we realize output power 6.02W, linewidth full-width half-maximum (FWHM) 0.3nm 1.91-μm Tm:YLF laser with a VBG as a resonator, and we compare the output laser performance with the VBG and the conventional mirror. Secondly, the effects of pump wavelength, temperature of laser crystal, output coupler transmission and cavity length on laser performance are discussed by experiment. In addition, by improvement of the experiment, wavelength stable 1.91-μm laser with output power 10.0W is obtained using coated VBG, with the optical-optical conversion efficiency of 32.1% and slope efficiency of 39.8% respectively, and the linewidth FWHM is 0.1nm, beam quality factor M2 is 1.54. Furthermore, the experiment of Tm:YLF laser pumped Ho:YAP laser is investigated, and we realize 2118nm continuous wave output. Moreover, the thermal effect of wavelength selectivity of VBG is studied by experiment. Red shift of the output wavelength occurs with the increase of temperature of VBG. Finally, according to theoretical and experimental analysis, a narrow-linewidth, high-output power and stable output Tm:YLF laser is designed.更多还原