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AgGaS2, AgGaSe2 Crystal
AgGaS2 is a nonlinear crystal which can be used for the middle and deep infrared applications. AgGaS2 crystal has 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.
AgGaS2 crystal (AGS) is transparent from 0.53 to 12 µm. It can be used 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; in direct infrared countermeasure systems, and for SHG of CO2 laser. Thin AgGaS2 crystal plates are popular for ultrashort pulse generation in mid IR range by difference frequence generation employing NIR wavelength pulses.
Comparison of Infrared Nonlinear Crystals
- 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. It is successfully used in diverse applications: up-conversion of CO2 laser light to near IR range via mixing with 10.6 µm; sum frequency generation of CO and CO2 laser radiation; efficient SHG of pulsed CO, CO2 and chemical DF-laser; OPO light generation in mid infrared when pumped by erbium and holmium lasers.
- 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. Tuning within 2.5–12 µm has been obtained when pumping by Ho:YLF laser at 2.05 µm; as well as non-critical phase matching (NCPM) operation within 1.9–5.5 µm when pumping at 1.4–1.55 µm. AgGaSe2 (AGSe) has been demonstrated to be an efficient frequency doubling crystal for infrared CO2 lasers radiation.
- 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; OPG light generation within 3.5–18 µm. Thin GaSe crystal plates are also used for fs THz generation. It is impossible to cut the crystals for certain phase matching angles because of material structure (cleave along [001] plane), which limits the application areas.