Development of a mid-infrared tunable optical parametric oscillator pumped by a Q-switched Tm,Ho:YAG laser

Abstract

A compact and high-energy pulsed mid-infrared laser using an optical parametric oscillator (OPO) has been developed using a diode-pumped and Q-switched Tm,Ho:YAG ceramic laser with a wavelength of 2.09 µm as a pump source. A singly-resonant OPO with a 20 mm long AgGaSe 2 crystal was used, and the crystal was set at an angle normal to the pump beam. The output idler pulse energy was up to about 200 µJ with the pump energy of about 6 mJ for both the type I and type II phase matching conditions. The wavelength of the idler pulses was 5.97 and 6.37 µm for type I and type II, respectively. The output characteristics predicted using a model calculation were in good agreement with the experimental results. It is suggested that the output idler pulse energy in the experiment is limited by the surface damage threshold of the AgGaSe 2 crystal. By increasing the pump beam diameter from 1 to 3 mm (3-fold) and the pump energy from 6 to 54 mJ (9-fold), the idler pulse energy of 1.8 mJ (= 200 µJ × 9) will be obtained without increasing the pump intensity and without saturation of the output idler pulse energy.