Mid-infrared (5–12-µm) and limited (55–85-µm) single-knob tuning generated by difference-frequency mixing in single-crystal AgGaS_2

We describe tunable 5-12-microm mid-infrared generation in single-crystal silver gallium sulfide (AgGaS(2)), from nonlinear optical difference-frequency generation. Signal and idler waves obtained from a Nd:YAG laser-pumped LiNbO(3) optical parametric oscillator (OPO) were mixed in AgGaS(2) crystal to yield difference-frequency waves. For the efficient generation of difference frequency, an unstable resonator was employed as the OPO to reduce output beam divergence. A maximum difference-frequency power of 95 microJ/pulse was obtained near 7.5 microm for a 1-cm-long AgGaS(2) crystal. Spectral noncritical phase matching within a specific tuning range was also investigated that permitted limited single-knob tuning (5.5-8.5 microm) of the difference-frequency generator.