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(WO 4 ) 2 crystal with 15 at.% thulium doping of the overgrown layer, which is only 80 μm thick. A single double pass of the pump radiation from the diode-laser ensures efficient 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 ∼ 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.