Studies On The Q-Switched Laser Characteristics Of Ho:YVO₄ Crystals Pumped By 1.94μm Lasers

Q-switched technology can achieve high peak power and nanosecond laser output, which is widely used in laser radar, laser ignition, ranging, optical data storage and other fields. Compared with other wavelength of the laser, 2μm lasers because it is at atmospheric propagation windows and eye-safe wavelength characteristics, has more obvious advantages in laser sensor, laser medical, materials processing, military and other fields. Ho:YVO4 crystal has higher thermal conductivity, better mechanical properties, stabilized chemical properties, which can be used as the laser medium to achieve 2μm laser output. At present, the reports for Ho:YVO4 lasers only limit to continuous output, the Q-switched Ho:YVO4 laser has not been reported. This paper aims to study the Q-switched characteristics of Ho:YVO4 lasers, in order to obtain high efficiency Q-switched Ho:YVO4 laser output.First, in the design progress of Tm: YAP resonant cavity, we utilized the double FP structure to control the laser wavelength. When the pump power reached to 116.5W, we obtained the 20.4W continuous laser output, corresponding to the slope efficiency of 24.8%. The laser output wavelength was about 1938.42 nm, and the beam quality was about M2=2.2. Then, the active and passive Q-switched characteristics of Ho:YVO4 lasers were analyzed to establish the quasi-three-level active and passive Q-switched rate equation. By numerically soluted the rate equations, we can simulate the experimental parameters(pulse width, pulse peak energy and peak power) for the active and passive Q-switched Ho:YVO4 lasers.On the basis of previous work, the active Q-switched Ho:YVO4 lasers pumped by Tm:YAP laser was researched. By compared the different transmission of output coupler, we decided to use the output coupler transmissions of 30% to achieve the Qswitched Ho: YVO4 laser output. When the repetition frequency was set to 9k Hz, the output pulse width was about 21.3ns, the average output power was about 3.9W. The laser output wavelength was about 2051.9nm, and the beam quality was about M2=1.09.Finally, the passive Q-switched Ho:YVO4 lasers pumped by Tm3+ fiber laser was researched. In the process of passively Q-switched experiment, a 7.1W average output power of passively Q-switched laser output was obtained for the absorption pump power of 30.4W, corresponding to the slope efficiency of 28.6% and optical conversion efficiency of 23.4%. The pulse width of passive Q-switched laser was 177.0ns, the peak energy was about 53.4μJ, corresponding to the peak power of 0.30 k W, and the pulse repetition frequency was about 132.2k Hz. The beam quality in horizontal and vertical directions were Mx2 = 1.15 and My2 = 1.09, respectively.