Passively <i>Q</i>-Switched Thulium Microchip Laser

We present the first passively <i>Q</i>-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 TEM₀₀ mode with M² < 1.1. The <i>Q</i>-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-<i>μ</i>m 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 TEM₀₀ 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_01∗-doughnutlike transverse mode. In all the cases, no active cooling is applied to the gain medium.