Chromium-doped zinc selenide gain media: From synthesis to pulsed mid-infrared laser operation

This paper provides an overview of the experimental work performed in our research group on the synthesis, spectroscopic investigation, and laser characterization of chromium-doped zinc selenide (Cr2+:ZnSe). By using diffusion doping, 40 polycrystalline Cr2+:ZnSe samples with ion concentration in the range of 0.8 x 10(18) to 66 x 10(18)ions/cm(3) were prepared. From the absorption data, temperature-dependent diffusion coefficient of chromium and losses at the lasing wavelength were measured. In luminescence measurements, the concentration dependence of the fluorescence lifetime and fluorescence quantum efficiency was determined. During continuous-wave operation, the optimum concentration for lasing was determined to be 8.5 x 10(18) ions/cm(3) at an incident pump power of 2.1 W for 1800-nm pumping. During gain switched operation, intra-cavity pumping with a 1570-nm optical parametric oscillator resulted in continuous tuning between 1880 and 3100 nm. By employing dispersion compensation with a MgF2 prism pair, Kerrlens mode-locked operation was also demonstrated at 2420 nm, resulting in the generation of 95-fs pulses with an average output power of 40 mW and spectral bandwidth of 69 nm. The time-bandwidth product of the pulses was further measured to be 0.335 close to the expected value of 0.315 for sech(2) pulses.