CW laser operation of a highly-doped Tm:KLu(WO4)2/KLu(WO4)2 thin disk epitaxial laser

We demonstrate the first thin disk epitaxial Tm-laser based on the monoclinic KLu(WO4)(2) with 15 at. % doping. The doped epitaxial layer serving as an active medium is only 80 mu m thick. The large absorption enables efficient pumping with only a single double pass of the pump radiation from the diode-laser. For output coupling between 0.4% and 2.8%, the slope efficiency in the continuous-wave regime is in the 7-11% range and the laser threshold is 1.5...2.5 W of absorbed pump power. The laser emission spectra are centered at similar to 1850, 1915 and 1940 nm for output couples of 2.8%, 1.6% and 0.4% transmission, respectively. In all cases the emission spectra are "structured", consisting of a number (typically 5 ... 10) of narrow emission lines spread irregularly over 15 ... 30 nm.