Silver Thiogallate (AgGaS2) has been demonstrated to be an efficient frequency doubling crystal for infrared radiation such as the 10.6 µm output of CO2 lasers. Silver Thiogallate (AgGaS2) has also been shown as an excellent crystal for non-linear three-wave interactions.
With suitable pump lasers, Silver Thiogallate (AgGaS2) optical parametric oscillators (OPO's) can produce continuously tunable radiation over a wide range of wavelengths in the infrared. Using 2050 nm pump laser, an optimally designed AgGaS2 OPO is tunable from about 2.5 to 12.0 µm. The output range can be extended by the sum or difference frequency mixing (SFM/DFM). This crystal has a high non-linear coefficient, high damage threshold, and a wide transmission range. Silver Thiogallate (AgGaS2) also has low optical absorption and scattering, low wavefront distortion. Among commercially available crystals, AgGaS2 has the highest figure of merit for non-linear interactions in the near and deep infrared. The availability of this crystal has stimulated new activities exploiting its interesting properties.
A closely related crystal, Silver Selenogallate (AgGaSe2), is also available. It's bulk quality is excellent across the transmission range. There is no residual e-ray absorption centred around 1800 nm. The phase matching and non-linear optical properties of AgGaSe2 allow various SFM/DFM interactions from the visible to mid-IR, these includes non-critically phase matched DFM using selected wavelengths (available from tunable dye and Ti:Sapphire lasers) and OPO's pumped with commonly available Nd:YAG lasers.

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