Efficient KY_1-x-yGd_xLu_y(WO₄)₂:Tm³⁺ channel waveguide lasers

Gd3$+$(29.5\%)-Lu3$+$(29.0\%)-Tm3$+$(1.5\%) co-doped KY(WO4)2 layers were grown onto KY(WO4)2 substrates by liquid-phase epitaxy. Ridge-type channel waveguides with a thickness of 6.6 $\mu$m and a width of 7.5--12.5 $\mu$m were microstructured 1.5 $\mu$m deep by Ar$+$-beam milling and overgrown with pure KY(WO4)2 as a cladding layer. An upper limit of ~0.11 dB/cm for the waveguide propagation loss at the laser wavelength was determined. Laser experiments with butt-coupled dielectric mirrors demonstrated maximum output powers of 149 mW and 76 mW and slope efficiencies of 31.5\% and 17.0\% when pumping at 794 nm and 802 nm in TM and TE polarization, respectively. The lowest threshold was 7 mW. The laser wavelength was found to shift from 1930 nm via 1906 nm to 1846 nm for outcoupling efficiencies from 2\% via 8\% to 2x8\%.