Efficient CO2 laser SHG in a GaSe crystal

In GaSe single crystals, efficient second harmonic generation (SHG) of a CO2 laser has been obtained with a pulse repetition rate up to 100 Hz. The phase-matching angles in GaSe have been measured at pumping wavelengths of 9.3, 9.6, 10.3, and 10.6 microns. Also, the threshold power density of the surface optical damage and of the formation of a plasma jet on the GaSe surface are measured. In a 0.65-cm thick GaSe sample, SHG efficiency up to 9 percent has been achieved. A comparison is made between GaSe and ZnGeP2 as materials for CO2 laser SHG.