Research On Acousto-opitic Q-switched Ho:YAP Laser Pumped By 1.9μm Laser

Ho-doped laser with output central wavelength range at 2μm is promising in some fields,such as laser ranging,laser medical treatment,industrial processes,optical communication and life sciences.In addition,it can also be used as an efficient pumping source for 3-5 um tunable mid-infrared optical parametric oscillator.The main research significance of the paper is to achieve efficient laser output of narrow linewidth at 2μm,and provide high-quality pump source for mid-far infrared lasers.In theory,the energy level structure with Ho³⁺doped is introduced firstly.The light-emitting mechanism of Ho³⁺doped laser is expounded according to the energy level structure.The rate equation of 1.9μm laser-pumped Ho:YAP CM laser is solved,and the threshold power and output power of the laser are analyzed through simulation.The rate equation of 1.9μm laser-pumped Ho:YAP acousto-optic Q-switched laser is solved,and output characteristics like laser pulse width are analyzed through simulation.Based on the thermal effect theory of 1.9μm laser-pumped Ho:YAP crystal,the temperature distribution inside the crystal is simulated and analyzed by the COMSOL software.According to the results of theoretical analysis,the design and experiment of 1.9μm pumped Ho:YAP laser are carried out.On the basis of the theory of cavity resonators,a dual-LD end-pumped Tm:YAP CW laser is designed under the existing experimental conditions.A stable 1.9μm laser-pumped Ho:YAP straight-cavity resonator and a four-mirror rectangular-cavity resonator are designed,and the mode matching with different resonator parameters is analyzed.Finally,based on the Ho:YAP four-mirror rectangular cavity laser,a narrow-linewidth Ho:YAP laser by 1.9μm laser pumped is designed.In the experiment,the double LD end-pumped Tm:YAP CW laser is selected as the pump source of the Ho:YAP laser.The output power of Tm:YAP laser ranges from 0 to24.61 W and the central wavelength of output is 1989.01 nm.Ho:YAP crystals with doping concentration of 0.8 at%and size of 4×4×25 mm³ are selected for the experiments in the paper.Firstly,experiment is carried out on 1.9μm laser-pumped Ho:YAP linear cavity CW laser.At the maximum pump power,the maximum output power of CW laser is 8.54W,the slope efficiency is 36.39%,the linewidth is 1.84 nm and the wavelength is 2118.03 nm.The maximum average output power of 7.49W is obtained at the maximum pumping power and repetition frequency of 5 kHz.The laser’s wavelength is 2129.35 nm and the linewidth is0.94 nm.At the repetition frequency of 1 kHz,the narrowest output pulse width is 93.1 ns.Experiment is carried out on 1.9μm laser-pumped Ho:YAP rectangular-cavity CW laser.At the maximum pump power,the maximum utput power of CW laser is 5.25 W,the linewidth is 0.94 nm and the wavelength is 2129.27nm.The maximum average output power of 4.62W is obtained at the maximum pumping power and repetition frequency of 5 kHz.The laser’s wavelength is 2129.34 nm and the linewidth is 0.74 nm.At the repetition frequency of 1 kHz,the narrowest output pulse width is 115.6 ns.Finally,experiment is carried out on1.9μm laser-pumped Ho:YAP self-injected laser.At the maximum pump power of 24.61W,the maximum output power of CW laser is 5.06 W,the linewidth is 0.42 nm and the wavelength is 2129.31nm.The maximum average output power of 4.57 W is obtained at the maximum pumping power and repetition frequency of 5 kHz.The laser’s wavelength is2129.22 nm and the linewidth is 0.21 nm.At the repetition frequency of 1 kHz,the narrowest output pulse width is 104.2 ns.The practical effect of the self-injection technology is achieved on laser linewidth narrowing at the repetition frequency through experiments.The experimental results show that the linewidth of the self-injected Ho:YAP laser can be narrowed.