Fe:ZnSe laser oscillation under cryogenic and room temperature

Abstract

The goal of this work was to design and investigate a Fe:ZnSe laser operating at room and cryogenic (down to liquid nitrogen) temperature. Pumping was provided by a Q-switched Er:YAG laser at the wavelength of 2.94 μm, the output energy 15 mJ, pulse duration 120 ns, and the 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:ZnSe crystal placed in the vacuum chamber cooled by liquid nitrogen. The resonator was formed by a dichroic pumping mirror (T = 78 % at 2.94 μm and R = 100 % at 4.5 μm), and a concave output coupler (R = 95 % at 4.5 μm, r = 500 mm). Fluorescence spectra and lifetime of the bulk Bridgman-grown Fe:ZnSe crystal in the range from room temperature down to liquid nitrogen temperature were measured as well as the output characteristics of the Fe:ZnSe laser. The shift of the generated spectral line maximum of ~ 400 nm towards the shorter wavelengths was found for the change of temperature from room to the liquid nitrogen. Also the increase of lifetime was measured from 300 ns at the room temperature up to 100 μs at the temperature of 130 K. Maximum of generated output radiation at 130 K was 150 μJ with the central emission wavelength of 4.1 μm. At the room temperature the central emission wavelength of 4.45 μm was measured with the spectral line-width of ~100 nm. The generated output energy was 1.3 mJ. The comparison of results obtained for Fe:ZnSe active material with the new bulk Fe,Cr:ZnMgSe crystal was also made. The results obtained for Fe:ZnSe active material were compared with the investigation of new bulk crystal Fe,Cr:ZnMgSe.