Laser-diode-pumped Cr:ZnSe CW laser tunable in mid-IR range of 2.05-2.65μm

The spectral and laser characteristics of two anti-reflection (AR) coated Cr:ZnSe single crystals 3 mm and 5 mm long were investigated under ~1.7 μm laser diode pumping. The crystals were assembled in a copper holder actively cooled by circulating water. Room temperature absorption and fluorescence spectra were measured, together with the fluorescence lifetime of Cr2+ ions were measured. The influence of the pump pulse durations on the output laser power was investigated. The mean output power of ~2.7 W in CW mode at the wavelength of ~2.4 μm (~24% slope efficiency) was obtained with the 5 mm thick AR coated sample. In this case the M2 beam parameter of ~1.1±0.1 and the beam waist diameter of ~42±4 μm which corresponds to the maximum (in the beam waist) laser power density of ~200 kW/cm2. Furthermore, using a MgF2 birefringent plate, the laser output was tuned from ~2.05 μm up to ~2.65 μm with a spectral linewidth of ~5-10 nm and a Gaussian beam profile. The mean laser output power in the broad mid-infrared range of ~2.1-2.52 μm exceeded 1 W, which corresponds to a power density of at least ~73.5 kW/cm2.