Thulium channel waveguide laser with 70% slope efficiency in a monoclinic double tungstate

Laser experiments on 1.5at.%, 5at.%, and 8at.% thulium-gadolinium-lutetium-yttrium co-doped, buried, ridgetype channel waveguides in a monoclinic potassium double tungstate demonstrate a maximum slope efficiency of 70% and output powers of 300 mW at ~1.9 μm.