Orange surface waveguide laser in Pr:LiYF4 produced by a femtosecond laser writing

Depressed-cladding surface channel waveguides were inscribed in a 0.5 at.% Pr:LiYF4 crystal by femtosecond Direct Laser Writing. The waveguides consisted of a half-ring cladding (inner diameter: 17 µm) and side structures ("ears") improving the mode confinement. The waveguide propagation loss was as low as 0.14 ± 0.05 dB/cm. The orange waveguide laser operating in the fundamental mode delivered 274 mW at 604.3 nm with 28.4% slope efficiency, a laser threshold of only 29 mW and linear polarization (π), representing record-high performance for orange Pr waveguide lasers.