Studies On Power-scaling Of Singly-doped Tm³⁺ Lasers

Ho³⁺laser pumped by Tm³⁺laser is an efficient2μm laser source which is widelyused in military, spectroscopy and so on. Improving single-crystal Tm³⁺laser outputpower can facilitate the structure, which is valuable. On the Basis of attractive1.9μmTm:YLF laser and Tm:YAP laser, their power-scaling techonology would beinvestigated in theory and experiment in this thesis.Based on crystals’ absorption and emission spectrum, output wavelength ofTm:YLF and Tm:YAP laser have been analyzed from the standpoint of gain crosssection. According to the eatablished Tm³⁺laser quasi-three-level laser model, theinfluence of doped concentration and length of crystal on laser conversion efficiencywas discussed, and adaptable concentration-length product of Tm:YLF and Tm:YAPhave been obtained. The thermal effects of rod and slab have been analyzed based onthe constructed thermal model. The thermal effects can be relieved by using compositecrystal, decreasing doped concentration, increasing crystal’s length, and utilizing slabstructure. In experiment, the thermal focal length of Tm:YAP was measured. Accordingto the method that beam quality M2factor to deducing thermal focal length andtransmitting metrix describing the thermal lens effects, the beam quality and beam waistradius of Tm:YLF laser have been measured, and he thermal focal length of compositeTm:YLF and transmission results of equivalent matrix were deduced. The results werein agreement with the simulation results under Gaussia beam assumption. In addition,due to the serious thermal effects of Tm:YAP, a cavity that can endure thermal focallength of less than20mm, and has nearly continuous stable zone was designedaccording to resonater’s stability.On the basis of previous work, Tm:YLF laser was investigated. Under the pumpwaist of0.45mm, with the pump power of72.3W,27.5W was obtained for3×3×12mm³Tm（3.5at.%）:YLF laser, and crystal was fractured when pump power was75W. Outputpower was increased by using composite crystal, decreasing doped concentration,increasing crstal’s length, and utilizing slab structure. Among these, for1.5×12×20mm³Tm（2.5at.%）: YLF slab,72W at1.908μm with narrow linewidth was obtained underpump power of187.3W, with slope efficiency of43%. Additionally, study of differentaxis-cut Tm:YAP laser was carried out. The resonater parameters were optimized indesigned cavity. For pump waist of0.32mm, the maximum output power of a-cut2×2×10mm³Tm（3.5at.%）:YAP laser was24.5W under the pump power of79.6W, andthe rod was fractured with pump power of81W. When lower doped concentration1×6×12mm³Tm（2at.%）:YAP slab was used, incident pump power and output powerwere increased. As much as35.3W at1.94μm with narrow linewidth was achieved under the pump power of115.8W, corresponding to the slope efficiency of36%. For c-cut3×3×16mm³Tm（3.5at.%）:YAP laser, when injected86.3W,26.5W at1.99μm wasachieved, but the slope efficiency was abnomal.1×6×16mm³Tm（3.5at.%）:YAP and1.5×11×16mm³Tm（3.5at.%）:YAP slab was used to relieve thermal effects and improvelaser performance. For latter,44W at1.99μm was obtained under the pump power of110.7W, corresponding to the slope efficiency of46.4%.