A Passively $Q$ -Switched, CW-Pumped Fe:ZnSe Laser

We report the demonstration of high-average-power passively Q-switched laser oscillation from Fe²⁺ ions in zinc selenide. A semiconductor saturable absorber mirror was used as a passive Q-switch element. Using a 60% R outcoupler, the pump-limited output power was 515 mW. The spectral center of the laser was 4045 nm. The pulse repetition frequency (PRF) at maximum power was ~ 850 kHz with a corresponding minimum pulsewidth of 64 ns Full-Width Half-Maximum. The pulse energy and peak power were and 8.3 W, respectively. The average output power was limited only by available pump power and increased with a slope efficiency of 22%. No thermal rolloff of slope-efficiency was observed. The beam quality was measured to be M² ≤ 2.6. The temporal stability of the pulsed output was characterized. Thermal effects were shown to play a significant role in determining the PRF of the output.