Experimental Research On Output Characteristics Of Tm,Ho:YVO₄ Q-switched Solid-state Lasers

Laser diode pumped 2 ?m Q-switched solid-state lasers are widely applied in medical beauty, industrial communications, atmospheric sensing, nonlinear optical conversion technique and other fields, due to their compactness, high conversion efficiency, high power and good beam quality. Tm,Ho:YVO₄ laser crystal is low-temperature-sensitive. At low temperature, its absorption band is wide, the absorption cross-section is large, and the laser threshold is low, therefore, 2 ?m laser can be easily generated under the condition of refrigeration with liquid nitrogen. In this paper, the continuous and Q-switched laser output performances of Tm, Ho:YYO4 lasers are systematically investigated.In continuous wave ?CW? laser experiment, the mode matching conditions for various cavity types and cavity lengths are theoretically analyzed. The output wavelength of laser diode as a function of temperatures is measured. Then, the CW laser output performances under various mode matching conditions are investigated for the different temperatures of diode laser, cavity types, cavity lengths and output transmissions. The experimental results show that the CW laser output power is almost independent of cavity length. For the transmission of 40%,a maximum output power of 4.3 W is obtained at 11.5 W pump power,corresponding to the slope efficiency of 43% and optical conversion efficiency of 37%.By using the acousto-optic?AO? Q-switched scheme, the actively Q-switched Tm,Ho:YVO₄ laser is studied. In the actively Q-switched experiments, the output performances for different cavity types, cavity lengths and output transmissions are measured,which includ output power, pulse width, and single pulse energy and so on. The highest pulse energy is 1.142 mJ,the narrowest pulse width is 11 ns. In passively Q-switched experiment,a Cr2+: ZnS crystal is used as the saturable absorber. By adjusting various experimental parameters, a highest pulse energy of 0.189 mJ is obtained. The pulse width is 41 ns, the repeat frequency is 9.9 kHz, and the peak output power is 4.6 kW.The output wavelength and beam quality under various experimental conditions are also measured. It is found that there exist two center wavelengths at 2042 nm and 2055 nm for the Tm,Ho:YVO₄ laser, and their relative intensity changes under different experimental conditions. Comparing with the passively Q-switched laser, the CW and A-O Q-switched Tm,Ho:YVO₄ lasers have better beam quality.