Broadly tunable Tm:BaF2 and Tm:SrF2 lasers

Abstract

We report on the spectroscopic properties and first continuous-wave (CW) and broadly tunable operation of a Tm3+-doped barium fluoride (BaF2) crystal, comparing it with another fluorite-type compound, Tm3+:SrF2. Tm3+ ions in BaF2 exhibit broader emission around 2 µm (bandwidth: 235 nm) at the expense of a lower stimulated-emission cross-section (1.36×10−21cm2 at 1.86 µm) and a longer luminescence lifetime (12.03 ms) as compared with Tm:SrF2. The room-temperature CW Tm:BaF2 laser generated 184 mW at 1.88 µm with a slope efficiency of 54.8% exceeding the Stokes limit and a low laser threshold of 84 mW. In the quasi-CW regime, its output was further scaled to 0.56 W with even higher slope efficiency of 67.2%. By using an MgF2-based Lyot filter, continuous wavelength tuning of this laser from 1833 to 2002 nm (tuning range: 169 nm) was demonstrated. Tm:BaF2 is promising for ultrashort pulse generation from mode-locked lasers.