Study On High Repetition Frequency Ho:YAG Laser And It’s Pump Source Tm:YLF Laser

After a few researchers have introduced Ho-doped lasers, Ho³⁺ions have becomethe important ions which can be used of lasers because of their special spectralcharacteristics, such long lasers’ upper level lifetime, getting eye-safe and atmospherehigh transmittance2.1μm laser etc. since the1960s. In medicine, military, mechanicalprocessing and remote sensing fields,2.1μm lasers have important applications. Inparticular,2.1μm lasers can effectively get optoelectronic countermeasure sourcemiddle infrared3⁵μm lasers and far infrared8¹2μm lasers by pumping nonlinearcrystal. In order to obtain high power&high repetitive frequency middle infrared3⁵μm lasers, this article analyses and researches2.1μm Ho:YAG laser and it’s pumpsource Tm:YLF laser in theory and experiment.In the aspect of theory, the energy level transition mechanism and laser emittingmechanism of single-doped Tm³⁺laser&single-doped Ho³⁺laser are analysed, the rateequation theoretical model of single-doped Tm³⁺laser&single-doped Ho³⁺laser areestablished, and all kinds of parameters’ effect on Tm:YLF laser&Ho:YAG laser’soutput characteristics according to rate equation model are analysed. All kinds oftheoretical factors that effect on solid-sate laser relaxation oscillation frequency andrelaxation oscillation range are analysed, establishing the theory basis for solvingTm:YLF lasers’ relaxation oscillation issue effectively, providing the significanttheoretical guidance for Tm:YLF laser relaxation oscillation issue’s experimentalresearch. The temperature field and the theoretical thermal focal length of Tm:YLFcrystal&Ho:YAG crystal are analysed, providing the necessary parameters for realizingthe resonant cavities’ optimization design of Tm:YLF laser&Ho:YAG laser. thethermal damage threshold issue of Tm:YLF crystal is analysed and providing thetheoretical reference for obtaining Tm:YLF laser’s maximum pump power value.In the aspect of experiment, the thermal lens focal lengths of Tm:YLF&Ho:YAGcrystal and thermal damage threshold of Tm:YLF crystal are measured and providingthe reference data for Tm:YLF&Ho:YAG laser resonant cavities’ design and Tm:YLFcrystal’s maximum pump power value. The output-mirroro transmission&pump-lasermodel ratio’s effect on Tm:YLF power characteristics are tested, an effective cavitybicrystal and high power&high beam quality cavity tricrystal laser are conductedaccording to the analysis of test result, and the slope efficiency of49.4%is obtained inthe Tm:YLF laser with bicrystal cavity. During the Tm:YLF relaxation oscillationexperiment, the pump power and cavity length&output-mirroro transmission’s effecton relaxation oscillation frequency are tested, pump power and pump-laser model ratio’seffect on relaxation oscillation range are tested. By the experiment research for Tm:YLF relaxation oscillation issue, realising the high efficiency&high power Tm:YLF laserpower signal’s smooth output without peak and remove the working obstacles whenHo:YAG laser works at high repetitive frequency of some dozen kilohertz. According tothe single-crystal and bicrystal Ho:YAG laser resonant cavity parameter’s theoreticalanalysis, high power Ho:YAG laser experimental research work is conducted. Averagepower of more than40W and conversion efficiency of⁵0%are realized in both ofsingle-crystal and bicrystal Ho:YAG laser resonant cavity. One hundred watt bicrystalHo:YAG resonant cavity is proved feasible. By bonding and nonbonding Ho:YAGcrystal’s experiment comparision, finding bonding Ho:YAG crystal’s conversionefficiency is a little bit higher than that of nonbonding crystal. That proves bondingHo:YAG crystal’s advantage with high power pump. At last, by single-crystal Ho:YAGlaser resonant cavity, the ZGP OPO is experimented, and then OPO slope efficiencyreaches51.6%&optical-optical conversion efficiency reaches42.1%. By knife-edgemethod, the3⁵μm laser’s beam quality factor （M²） of4.2with10W is measured. ByHgCdTe detector, the3⁵μm laser’s pulse width of18.5ns with16.0W is measured.Finally, considering the lower level of experimental result compared with internationaladvanced level, putting forward the methods of improving middle infrared ZGP OPOefficiency and beam quality.