Study On Injection-locked Tm, Ho:YAP Laser

2μm solid-state lasers used as transmitter for Doppler wind lidar and Differential absorption lidar have become the research point of the lidar. Injection-locked 2μm solid-state lasers meet the requirements of light source for lidar due to their high energy, high beam quality, narrow linewidth, stable frequency and single frequency pulse laser output. In this paper, injection-locked Tm,Ho:YAP solid-state laser has been investigated theoretically and experimentally.Theoretically, firstly, based on level translation and energy transfer of Tm, Ho co-doped laser, the quasi-four-level rate equations of CW and Q-switch Tm,Ho laser operated in 77K are established. The analytical formula of initial upper level population inversion density is obtained. The mainly factors infect the output pulse width are discussed. Secondly, the theory of injection-locked is analyzed according to the classical theory model. The influence factors of mode coupling between the master laser and slave laser are analyzed. The minimum injected power which is essential to the injection-locked is discussed.Experimentally, injection-locked Tm,Ho:YAP laser is realized. The Tm,Ho:YAP master laser is a single-longitudinal-mode (SLM) operation laser by combining use the microchip structure and placing a ray filter outside the microchip laser. The influent factor of multi-mode oscillation in the cavity to the stability of output power and frequency are discussed. The reasons of the bad beam quality are also discussed. The slave laser is designed to be a ring laser, which is convenient for injection-seeded. Experimental studies on CW and Q-switched laser are carried out under different cavity length and output coupler. Then the optimum parameters of the cavity are selected. Good mode macthing between the master and slave laser is achieved by intensive designed. With the control of injection-locked servo system, the injection-locked Tm,Ho:YAP laser is obtained firstly. At repetition frequency of 100Hz, pulse energy of 3mJ and pulse width of 270ns is achieved. Under injected locking, the pulse buildup time shortened obviously. And the stability of output pulse energy and width is improved. The injection-locked laser is single frequency pulse laser verified by beat frequency measurement. Finally, a coherent laser Doppler velocity measurement experiment is carried out by using injection-locked Tm,Ho:YAP solid-state laser. The results of the experimental treatment are in good agreement with the actual speed, which means that it is possible to use injection-locked 2μm solid-state lasers to be as the light source of lidar at home.In order to expand the scope of laser materials applied to the injection-locked 2μm solid-state laser, injection-locked Tm,Ho:YVO₄ laser is realized. At repetition frequency of 20Hz, the pulse energy is 2mJ and pulse width is 70ns. Due to its serious thermal effects, it is difficult to achieve higher repetition rate and high pulse energy output of Tm,Ho:YVO₄ laser. And because of its large gain cross-section, the pulse width of Tm,Ho:YVO₄ laser is quite narrow. Therefore, compared with Tm,Ho:YVO₄ crystal, Tm, Ho:YAP is more suitable to be the laser medium as the light of lidar.