AgGaS2 is among the few nonlinear crystals that can be used for
middle and deep infrared applications. It exhibits transparency in the range of 0.53 to 12 µm.
AgGaS2 crystal has a large effective optical nonlinearity, a broad spectral acceptance,
and a wide angular acceptance. Infrared laser between 3 to 12µm can be generated via
Nd:YAG pumped OPO and DFG with diode and Ti:Sapphire lasers.
AgGaS2 crystal (AGS) can be used in
OPOs that 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 CO and CO2 laser. Thin
AgGaS2 crystal plates are popular for ultrashort pulse generation in mid
IR range by difference frequence generation employing NIR wavelength pulses.
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 CO, CO2 lasers radiation.
2. ZnGeP2(ZGP):
ZGP crystal 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
CO2 and chemical DF-laser; OPO light generation in mid infrared when pumped
by erbium and holmium lasers.
3. GaSe:
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.
