Experimental Studies On Tm:YAP Slab Laser With High Power

The emitting wavelength of2μm lasers in mid-infrared spectral region is inside thesafe absorpting band of human eye and the atmosphere transmission window. They arewidely applied to laser medical treatment, photoelectrical conflict, and the fabricatingand processing of materials. Tm:YAP laser crystal is promising for its strong ability toresist damage, excellent thermodynamic properties. Besides, its emitting wavelength islocated in the absorbing peak of crystals like Ho:YLF. All of the advantages makeTm:YAP to be an excellent2μm laser pumping source. However, the thermal lens effectrestricts the output of high-power1.9μm laser. Therefore, in this thesis, we devotedourselves to the research of slab Tm:YAP laser with quasi-three energy levels generationmechanism. To gain the high power, high beam quality1.94μm laser output, weinvestigated the thermal lens effect and its compensation method so.Firstly, according to the energy level transition theory, we set up the theoreticalmodel of quasi three-level rate equation of the Tm ion doped by considering the energyup-conversion and cross relaxation. And we analyzed the influence of the factors relatedto the pump spot, resonator, and crystal parameters versus output performance of thelaser. Based on the heat conduction equation, a heat distribution model of slab lasercrystal has been built up, and the temperature and stress distribution on every crosssurface has been simulated. Later, we simulated how the thermal focal length ofTm:YAP laser varied with pumping power on the foundation of the generationmechanism of thermal lens effect. In the end of this part, we designed the resonantcavity structure with a single Tm:TAP crystal and double Tm:TAP crystals respectively,which could hold the smallest thermal focal length and the largest stable section, inaccordance with ABCD law and the stable conditions of resonant cavity.Based on the former research, we carried out the experiment of continuous-wavesingle crystal Tm:YAP laser at room temperature. In this process, we introduceddouble-end-pumping method to improve pumping power, and adopted the doubleconcave cavity structure to compensate the thermal lens effect of Tm:YAP, andemployed the F-P etalon to select the output wavelength. Eventually, we obtained the1938.5nm laser output of48W, corresponding the slope efficiency and optical-to-opticalconversion efficiency of43.6%and34.3%respectively. When the output power wasincreased from4.94W to47.1W, the center wavelength drifted from1938.4nm to1938.8nm. With output power of25W and35W, the beam quality factors we acquiredwere4.11and4.16respectively. Based on the former experiment, we further executed the experiment ofcontinuous-wave laser with two Tm:YAP crystals at room temperature. Finally anoutput power of69.5W at1.94μm with the pump power of257W was gained. Byapplying the Tm:YAP laser as the pumping source of L-shaped Ho:YLF laser, we got a2062.4nm laser output of23.1W with the slope efficiency of47%and theoptical-to-optical conversion efficiency of nearly50%when the Tm:YAP output powerwas54.7W. Operating at Q-switched mode，a maximal output energy of18mJ and pulsewidth of22.6ns was obtained when the pulse repetition rate was set as1kHz.