Passively Q-switched Tm 3+ :LiGdF4 laser using Cr 2+ :ZnSe as saturable absorber

Lasers based on the Tm3+-ion (Tm) emission near 1.9 ?m are interesting for many medical applications [1], remote sensing (LIDAR), as well as for pumping optical parametric oscillators (OPOs) aimed at frequency down-conversion into the mid-IR. High pulse energy and peak power are advantageous for these applications since they can be achieved at relatively low average power if compared to the CW regime. While high energies have been demonstrated by active Q-switching, passive Q-switching (PQS) is much simpler and cheaper to realize and more importantly, shorter pulses are generated with higher peak power. In recent years, PQS of diode-pumped solid-state (DPSS) lasers by the use of intracavity saturable absorbers (SA), was successfully demonstrated in several CW-pumped, bulk Tm-doped materials. The best results so far, for any DPSS PQS Tm-doped laser, have been achieved, using fluoride hosts - Tm:YLF and Tm:LLF [2], combined with Cr:ZnS SAs. In the present work we investigate the PQS performance of Tm-doped LiGdF4 (GLF). This is a relatively new laser crystal isomorphous to the well-known YLF and LLF, in which the dopant substitutes Gd3+ host ions. Whilst CW and mode-locked operation of Tm:GLF were previously studied, to the best of our knowledge, this is the first report of Q-switching of this laser medium.