Powerful and tunable operation of a 1-2-kHz repetition-rate gain-switched Cr : forsterite laser and its frequency doubling

We present a comprehensive study of the optimum operating regime in gain-sw itched Cr:forsterite lasers pumped at kilohertz repetition rates, comparing five crystals of similar quality but different dopant levels. The optimiza tion of the cavity design includes selection of the proper pump fluence to account for excited-state absorption, optimum matching of the pump and lase r modes, and consideration of thermal effects. As a result >1-W average out put power is demonstrated at 2 kHz. The maximum conversion efficiencies ach ieved at 1 kHz are 24.2% (slope) and 20% (absolute). Narrow-band operation of this laser is possible with a birefringent filter, which is a prerequisi te for efficient frequency doubling to cover the 585-660-nm part of the vis ible spectral range. Tunable second-harmonic generation in a temperature-tu ned noncritical scheme that employs LiB3O5 produces 60 mW of average power near 619 nm with 13.5% conversion efficiency. (C) 1999 Optical Society of A merica.