Non-linear crystal
AgGaS2, AgGaSe2, GaSe, ZnGeP2 Optolita

Due to their unique features, optical nonlinear crystals like ZnGeP2, AgGaSe2, AgGaS2, GaSe have gained tremendous interest for the middle and deep infrared applications. The IR crystals have large effective optical nonlinearity, wide spectral and angular acceptance, broad transparency range, non-critical requirements for temperature stabilisation and vibration control, and are easy to mechanically process (except for GaSe).

ZnGeP2 crystal (ZGP) has band edges at 0.74 and 12 µm. Its useful transmission range lies from 1.9 to 10.6 µm. ZnGeP2 has the largest nonlinear optical coefficient and relatively high laser damage threshold.

AgGaSe2 crystal has band edges at 0.73 and 18 µm. Its useful transmission range within 0.9-16 µm and wide phase matching capability provide excellent potential for OPO applications when pumped by a variety of currently available lasers.

AgGaS2 crystal (AGS) is transparent from 0.53 to 12 µm. Although its nonlinear optical coefficient is the lowest among the above mentioned infrared crystals, high short wavelength transparency edging at 550 nm is made use of in OPOs pumped by Nd:YAG laser; in numerous difference frequency mixing experiments with diode, Ti:Sapphire, Nd:YAG and IR dye lasers covering 3-12 µm range.

GaSe crystal has band edges at 0.65 and 18 µm. GaSe has been successfully used for efficient SHG of CO2 laser; SHG of pulsed CO, CO2 and chemical DF-laser (λ = 2.36 µm) radiation; upconversion of CO and CO2 laser radiation into the visible range; infrared pulses generation via difference frequency mixing of neodymium and infrared dye laser or (F-)-centre laser pulses; OPG light generation within 3.5-18 µm.