Broadly tunable OPGaAs OPO pumped by Cr:ZnSe laser

Abstract

Coherent sources that are broadly and continuously tunable in the mid- and longwave infrared are of interest for a variety of scientific, commercial, and military applications. The advantages in an OPO of quasi-phasematched materials like orientation-patterned gallium arsenide (OPGaAs) come at the cost of the angle tuning possible in birefringent nonlinear crystals. Temperature tuning is limited by the material’s dn/dT value, and lacks speed and stability. A better alternative is to tune the OPO by tuning the pump laser. Here we report an OPGaAs OPO pumped by a gain-switched Cr:ZnSe laser which was continuously tuned by an intracavity etalon. The etalon also narrowed the output linewidth to around 4 nm. The Cr:ZnSe laser operated at a repetition rate of 500 Hz with a 45 ns pulsewidth. The pump was focused to a spot size (1/e2) of 100 μm at the center of a simple linear resonator formed by two 5-cm ROC mirrors. The OPGaAs crystal was 14 mm long, with a period of 97 μm, and was mounted with no active cooling. Tuning the pump laser over a range of 90 nm (2385-2475 nm) produced OPO output over a range of almost 4.5 μm (3500-7450 nm). OPO tuning was ultimately limited by coatings on the crystals and the resonator mirrors, as the Cr:ZnSe laser is capable of much broader tuning as a pump source. A maximum slope efficiency of 21% was obtained, with a pulse energy threshold of 84 μJ.