Design and modeling of a passively Q-switched diode-pumped Thulium laser at 2.3 μm

Abstract

We report on a diode-pumped Tm:LiYF4 laser operating on the 3 H4 → 3 H5 transition (at ~2.3 μm) passively Q-switched by a Cr 2+ :ZnSe saturable absorber. This laser delivers a maximum average output power of 130 mW at 2304.6 nm with a nearly diffraction limited beam, a linear polarization (π) and no colasing at ~1.9 μm. The corresponding pulse characteristics (duration / energy) are 1.24 μs / 3.6 μJ at a repetition rate of 36 kHz. By power scaling under quasi-CW pumping, even shorter pulse durations of 870 ns and higher pulse energies of 6.1 μJ are achieved. The performance of the laser is simulated using a model of a quasi-four-level gain medium and a "slow" saturable absorber showing a good agreement with the experiment. The effect of the thermal lens of the saturable absorber on the pulse characteristics is discussed.