Theoretical and experimental investigations of small-signal gain for a diode-pumped Q-switched Cr:LiSAF laser

We present a theoretical model proving that up-conversion and thermal quenching of fluorescence strongly limit small-signal gain in a CW pumped Cr:LiSAF laser. We have a good agreement with experimental measurements of small-signal gain obtained with a new simple method. We have then optimized the gain in a Cr:LiSAF laser pumped by two 400-mW red diodes. The highest gain, 1.11 at 600 mW of absorbed pump power, is obtained if the pump spot is circularized inside the crystal and if the Cr:LiSAF is pumped on both sides. In Q-switched operation, this laser produces tunable pulses (up to 6.5 /spl mu/J at 10 kHz) between 800 and 900 nm.