Gain-switched Fe:ZnMgSe laser oscillation under cryogenic temperature

The spectroscopic and laser properties of bulk Bridgman-grown Zn1-xMgxSe single crystals with the various concentrations of Mg (x=0.19; x=0.27; x=0.38) were investigated in the wide temperature range. The pumping was provided by a 2.94 μm Q-switched Er:YAG laser with a maximal energy of 15 mJ in 120 ns pulse, repetition rate 1 Hz. Q-switched operation was achieved by the Brewster angle cut LiNbO3 Pockels cell placed between the rear mirror and the Er:YAG laser active medium. The pump radiation was directed into the Fe:ZnMgSe crystal placed inside the LN cooled dewar. The 55 mm long plane-concave cavity was formed by a dichroic pumping mirror (T = 92 % @ 2.94 μm and R = 100 % @ 4 - 5 μm) and a output coupler (R = 95 % @ 4.5 μm, r = 200 mm). The strong dependence of output pulse energy on temperature was observed for all samples. The maximum output Fe,Cr:Zn1- xMgxSe laser energy was 230 μJ and 180 μJ (for Mg concentration x=0.19 and x=0.38, respectively) for gain switched operation at 88 K. The central emission wavelength of ~ 4600 nm, ~ 4700 nm and ~ 4800 nm for Mg concentration x=0.19; x=0.27, and x=0.37, respectively at 88 K was obtained. The emission wavelength was found to increase up to ~ 4700 nm and ~ 4900 nm at 250 K for Mg concentration x=0.19 and x=0.38, respectively. This results show the possibility to obtain sufficiently longer oscillation wavelengths compared to previously studied Fe:ZnSe active medium especially at liquid nitrogen temperatures when pumping by free-running Er:YAG laser becomes possible. Fluorescence spectra and lifetimes of Fe2+ ions in different Zn1-xMgxSe crystals in the range from 250 K down to 80 K were also measured.