Mid-infrared (5-12-mu m) and limited (5.5-8.5-mu m) single-knob tuning generated by difference-frequency mixing in single-crystal AgGaS2

We describe tunable 5-12-mu m mid-infrared generation in single-crystal sil ver gallium sulfide (AgGaS2), from nonlinear optical difference-frequency g eneration. Signal and idler waves obtained from a Nd:YAG laser-pumped LiNbO 3 optical parametric oscillator (OPO) were mixed in AgGaS2 crystal to yield difference-frequency waves. For the efficient generation of difference fre quency, an unstable resonator was employed as the OPO to reduce output beam divergence. A maximum difference-frequency power of 95 mu J/pulse was obta ined near 7.5 mu m for a 1-cm-long AgGaS2 crystal. Spectral noncritical pha se matching within a specific tuning range was also investigated that permi tted limited single-knob tuning (5.5-8.5 mu m) of the difference-frequency generator. (C) 1999 Optical Society of America.