Room-temperature continuous-wave diode-pumped Tm:Ho:LuLF laser at 2.1μm Vikas Sudesh Science and Technology Corporation, Hampton, VA 23666, USA vikas_sudesh@hotmail.com Kazuhiro Asai, and Atsushi Sato Tohoku Institute of Technology, Taihaku-Ku, Sendai 982-8577, Japan Upendra N. Singh, Brian M. Walsh, and Norman P. Barnes NASA Langley Research Center, MS 468, Hampton, VA 23681, USA Abstract: CW laser action at room-temperature is demonstrated for the first time in Tm:Ho:LuLF. Output power in excess of 285mW, and slope efficiency of 32% were achieved experimentally. © 2004 Optical Society of America OCIS codes: (140.3580) Lasers, solid-state, LuLF, Holmium 1. Introduction There have been considerable interests in the development of continuous-wave (CW) high power diode-pumped mid-infrared lasers [1], for various applications including atmospheric remote sensing of CO 2 and H 2 O [2]. Fluorides have less severe up-conversion losses compared to garnets. Filer et al. [3], performed quantum mechanical calculations for various garnet and scheelite materials. The study predicted LuLiF 4 (LuLF) to be the most promising of YLF, LuLF and GdLiF 4 crystals. There have been some reports on pulsed, room temperature Tm,Ho:LuLF lasers [for example Ref. 4], however, no published work was found on cw Tm,Ho:LuLF lasers. In this paper we present, to the best of our knowledge, first demonstration of a diode pumped cw Tm,Ho:LuLF laser. In addition, Walsh et al. [5], recently measured the energy levels of the two lowest manifolds in Ho:LuLF, and the emission cross-section of the Ho 5 I 7 - 5 I 8 manifold. Using these data and others we calculated pump power threshold for Tm,Ho:LuLF laser. A comparison between the experimental and theoretical values is made. 2. Experimental setup Fig. 1. Schematic of the experimental setup. Figure 1 shows schematic of the setup of the LD pumped Tm;Ho:LuLF laser. A cw laser-diode (SDL 2382-P1) was used as a pump source. The laser-diode was temperature-tuned such that the center wavelength was 0.793 µm to match the absorption peak of the Tm ions. The size of the laser crystal was 4 mm x 3 mm x 2.7 mm (a x c x a-axes), with 2.7mm long a-axis is along the direction of laser oscillation. The crystal end-faces were Brewster cut at laser wavelength to minimize the reflection losses in the cavity. The crystal was sandwiched between two water-cooled copper heat-sink plates. A hemispherical laser cavity was formed by a flat high reflector at 2µm and a 0.5% 4x3x2.7 (axcxa) Collimating lens Brewester- cut Laser crystal 2μm l Laser diode Cylindrical Lens (f=5cm) Cylindrical Lens (f=30cm) Spherical Lens (f=15cm) HR mirror Output coupler ROC = 100mm WB19 © 2004 OSA/ASSP 2004