Er³⁺:YLiF₄ channeled waveguide laser near 2.7–2.8 µm fabricated by femtosecond laser inscription

We report, for the first time to our knowledge, a demonstration of robust waveguide lasing near 2.7–2.8 µm in an erbium-doped fluoride host. Femtosecond laser inscription was employed to fabricate 50- and 70-µm diameter channeled waveguides inside an Er³⁺:YLiF₄ crystal. The best power performance was obtained with the 70-µm diameter waveguide and 16% transmitting output coupler. The propagation loss and refractive index contrast were measured as 0.23 dB/cm and 7.1 × 10⁻⁴, respectively, for the 70-µm diameter waveguide. Both self-Q-switched (SQS) and continuous-wave (CW) operations could be obtained. During the SQS operation, as short as 240-ns pulses with average power of 51 mW, repetition rate of 368 kHz, and power slope efficiency of 15.2% were generated at the wavelength of 2717 nm with 465 mW of the pump power. During the CW operation, as high as 66 mW of output power was achieved at 2808 nm by using 460 mW of pump power at 798 nm, with a power slope efficiency of 19.6%.