Concentration dependence of fluorescence and lasing efficiency in Cr2+:ZnSe lasers

We investigated the effect of Cr2+ concentration on the fluorescence lifetime, fluorescence efficiency, and lasing performance of Cr2+:ZnSe lasers. In the experiments, polycrystalline Cr2+:ZnSe samples with concentrations of 0.34 × 1018–66 × 1018 ion/cm3 were prepared by diffusion doping. Spectroscopic measurements performed with Cr4+:YAG and Tm3+:fiber lasers show that the fluorescence efficiency decreases monotonically with increasing active ion concentration. Lifetime measurements and lasing characterization were also performed with a pulsed 1570-nm KTP optical parametric oscillator. In gain-switched operation, the highest output energy was obtained with the Cr2+:ZnSe sample having a Cr2+ ion concentration of 14 × 1018 cm−3. The power performance degrades with increasing concentration due to larger passive losses at the lasing wavelength. Furthermore, the pulse build-up time and the output pulsewidth decrease with pump energy and ion concentration. Finally, with a single set of optics, tunable output could be obtained in the 2520–3050 nm wavelength range.