Another material, which is very suitable for SHG in the mid-IR is Gallium Selenide (GaSe) non-linear optical single crystal, combining a large non-linear coefficient, a high damage threshold and a wide transparency range. The frequency-doubling properties of GaSe were studied in the wavelength range between 6.0 µm and 12.0 µm. GaSe has been successfully used for efficient SHG of CO2 laser (up to 9% conversion); for SHG of pulsed CO, CO2 and chemical DF-laser (l = 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; terahertz (T-rays) radiation generation. It is impossibile to cut crystals for certain phase matching angles because of material structure (cleave along (001) plane) limiting areas of applications.

Literature:
    • Wei Shi, Yujie J. Ding, Nils Fernelius, Konstantin Vodopyanov. Efficient, tunable, and coherent 0.18 - 5.27-THz source based on GaSe crystal: erratum. Optics Letters, (2003) v. 28, 2, 136-136
    • R. A. Kaindl, F. Eickemeyer, M. Woerner, T. Elsaesser. Broadband phasematched difference frequency mixing of femtosecond pulses in GaSe: experiment and theory. Appl. Phys. Lett. 75 (1999) 1060-1062
    • K. L. Vodopyanov. Parametric generation of tunable infrared radiation in ZnGeP2 and GaSe pumped at 3 µm. JOSA B, 1993, 10, 9, 1723

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