Efficient Tm:YAG and Tm:LuAG lasers pumped by red tapered diodes

E. Beyatli1, B. Sumpf2, G. Erbert2, and U. Demirbas3,4

Published in:

Conf. on Lasers and Electro-Optics/Europe and European Quantum Electronics Conf. (CLEO/Europe-EQEC 2019), Munich, Germany, Jun. 23-27, ISBN: 978-1-7281-0469-0, ca-7.2 (2019).

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Eye-safe, diode-pumped all-solid-state lasers working in the 2 µm region are favourable for many applications including remote sensing, medicine, and gas sensing. Tm-doped crystals such as Tm:YAG and Tm:LuAG are among the commonly employed laser gain media for this purpose. These systems are usually pumped by laser diodes operating around 780 nm [1]. The corresponding stokes limit for laser slope efficiency is then about 39%. However, for highly-doped samples, the two-for-one cross-relaxation process enables laser efficiencies exceeding this limit, and a slope efficiency of 59% has been reported from a 785 nm Ti:Sapphire pumped Tm:YAG laser, indicating a cross-relaxation efficiency of around 1.5 (one 780 nm pump photon generating 1.5 laser photons around 2 µm) [2]. As an alternative pumping approach, Stoneman et al. pointed out the possibility to pump Tm-based lasers around 681 nm, due to the much stronger absorption line at this wavelength [3]. Compared to 785 nm pumping, using the stronger 681 nm line warrants utilization of shorter Tm-crystals, which minimizes self-absorption losses [3]. Moreover, 681 nm pumping could also facilitate usage of thinner crystals in thin-disk geometry and/or could decrease the required number of bounces on the thin-disk for sufficient absorption of the pump light [4]. Moreover, pumping at a wavelength with stronger absorption coefficient creates a more densely populated gain medium, which could increase the effectiveness of cross-relaxation process. As a drawback, the stokes limited slope efficiency reduces to around 34% for 681 nm pumping, and decreased absorption lengths might also induce stronger thermal effects. In their early work, Stoneman et al. used a Ti:Sapphire laser operating at 681 nm to pump a Tm:YAG crystal, but the obtained slope efficiency was only around 35%, indicating a weak cross-relaxation process [3].

1 Department of Electrical-Electronics Engineering, Recep Tayyip Erdogan University, Rize, 53100, Turkey
2 Ferdinand-Braun-Institut, Leibniz Institut für Höchstfrequenztechnik, D-12489 Berlin, Germany
3 Laser Technology Laboratory, Antalya Bilim University, 07190 Dosemealti, Antalya, Turkey
4 Center for Free-Electron Laser Science, Deutsches Elektronen Synchroton (DESY), Hamburg, Germany