Effect of postgrowth processing technology and laser radiation parameters at wavelengths of 2091 and 1064 nm on the laser-induced damage threshold in ZnGeP2 single crystal

We report a study of the effect of postgrowth treatment of ZnGeP₂ single crystals (low-temperature annealing, irradiation with fast electrons, polishing of working surfaces) and the conditions of exposure to repetitively pulsed laser radiation [wavelength (2091 or 1064 nm), pulse repetition rate, beam diameter, exposure time, sample temperature] on the laser-induced damage threshold (LIDT) of the surfaces of these crystals. It is found that thermal annealing of ZnGeP₂ single crystals and their irradiation with a flux of fast electrons, which increase the LIDT at a wavelength of λ = 1064 nm, do not lead to a change in this threshold at λ = 2091 nm. It is shown that ZnGeP₂ elements with lower optical losses in the spectral range 0.7–2.5 mm have a higher LIDT at λ = 2091 nm both immediately after fabrication and after postgrowth processing. An increase in the threshold energy density of laser radiation by a factor of 1.5–3 at λ = 2091 nm is revealed with a decrease in the crystal temperature from zero to –60 °C. The fact of reversible photodarkening of the propagation channel of laser radiation in ZnGeP₂ in the predamage region of parameters is established by the method of digital holography.