Thin disk Tm-laser based on highly doped Tm:KLu(WO4)(2)/KLu(WO4)(2) epitaxy

Continuous wave (CW) Tm-laser operation is achieved for the first time using the thin disk laser concept and an epitaxial active element based on the monoclinic KLu(WO4)(2) crystal with 15 at.% thulium doping of the over grown layer which is only 80 mu m thick. A single double pass of the pumping due to the large absorption of the active layer. For output coupling between 0.4% and 2.8%, the slope efficiency in the CW regime is in the 7-11% range and the laser threshold amounts to 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 couplers 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.