Spectroscopy, modeling, and laser operation of thulium-doped crystals at 2.3 μm

Pulsed room-temperature lasers based on the thulium 2.3-μm ³H ₄- ³H ₅ transition have been achieved in 1.5% Tm:YAG, 2% Tm:LuAg, and 1.5% Tm:YLF crystals using a pulsed alexandrite laser at 785 nm as the pump source in a collinear geometry. The absorbed energy thresholds (slope efficiencies) for 1.5% Tm:YAG, 2% Tm:LuAg, and 1.5% Tm:YLF lasers are measured to be 1.2 mJ (14%), 1.8 mJ (13%), and 1.0 mJ (18%), respectively, which are in good agreement with the theoretically predicted results. The experimental results indicate 1.5% thulium to be the most optimum concentration for 2.3-μm laser action. The thulium lasers are tuned around 2.3 μm using an intracavity single birefringent plate of quartz.