Highly efficient Gd, Lu co-doped KYW:Yb³⁺ planar and channel waveguide lasers

Waveguide lasing is achieved in crystalline Gd3+, Lu3+ co-doped KY(WO4)2:Yb3+ (KYW) thin layers grown on undoped substrates. While the optimum Yb concentration for lasing of 1-3at.% leads to a refractive-index contrast between layer and substrate of only a few times 10-4, further increase up to 10-2 can be achieved by co-doping the layer with large amounts of optically inert Gd and Lu ions. The resulting fundamental-mode waveguides have much smaller thickness, thus greatly facilitating microstructuring by ion beam etching. In such KYW:Gd,Lu,Yb layers, in which the Yb ion exhibits spectropcopic properties very similar to those in KYW:Yb, we have demonstrated planar waveguide lasing with 82% slope efficiency and channel waveguide lasing with 61% slope efficiency, with pump thresholds of only 18 mW and 5 mW, respectively.