Fifty percent internal slope efficiency femtosecond direct-written Tm ³⁺:ZBLAN waveguide laser

We report a 790nm pumped, Tm³⁺ doped ZBLAN glass buried waveguide laser that produces 47mWat 1880nm, with a 50% internal slope efficiency and an M² of 1.7. The waveguide cladding is defined by two overlapping rings created by femtosecond direct-writing of the glass, which results in the formation of a tubular depressedindex- cladding structure, and the laser resonator is defined by external dielectric mirrors. This is, to the best of our knowledge, the most efficient laser created in a glass host via femtosecond waveguide writing.