Demonstrations of diode-pumped and grating-tuned ZnSe:Cr{sup 2+} lasers

Within the last few years, divalent-transition-metal-doped II-VI material class has been proposed as source of new tunable mid-IR lasers. Cr{sup 2+} is a prime laser candidate on account of its high luminescence quantum yield and the expectation that ESA would be absent. The first ZnSe:Cr{sup 2+} laser demonstrations were conducted in an end-pumped geometry with a tightly focused (0.2 mm spot) MgF{sub 2}-Co{sup 2+} laser beam, for a peak pump intensity well over 100 kW/cm{sup 2}, so laser threshold was easily reached. Grating tuning experiments were done by replacing the cavity high-reflector with a diffraction grating. The diode array was removed and pump beam from a MgF{sub 2}:Co{sup 2+} laser was focused onto the crystal using the same cylindrical lens. Output wavelengths were checked with a monochromator. The long-wavelength limit of operation was 2799 nm. Short-wavelength cutoff was 2134 nm; even though the emission cross section remains substantial, self-absorption inhibits laser operation