Passively $Q$ -Switched Thulium Microchip Laser

We present the first passively Q-switched thulium microchip laser. The diode-pumped laser incorporates a Tm:KYW gain medium and an InGaAs semiconductor saturable absorber mirror. The laser emits pulses with a duration of 2.4 ns at a repetition rate of 1.2 MHz with an average output power of 130 mW at a wavelength of 1905 nm. It operates in a fundamental TEM
₀₀
mode with M
²
<; 1.1. The Q-switched pulse train is very stable with pulse-to-pulse intensity fluctuations <;10% and a timing jitter of <;±50 ns. Our microchip laser appears well suited as a seed in pulsed 2-μm fiber amplifier systems for applications like material processing. In addition, we present new power scaling results for continuous-wave Tm-microchip lasers, achieving 1.6 W of output power in a fundamental TEM
₀₀
mode. The slope efficiency relative to the absorbed pump power is as high as 74%, and the optical-to-optical efficiency is 41%. A maximum output power of 2.6 W is achieved in a TEM
₀
·-doughnutlike transverse mode. In all the cases, no active cooling is applied to the gain medium.