Low-loss fs-laser-written surface waveguide lasers at >2  µm in monoclinic Tm³⁺:MgWO₄

Surface channel waveguides (WGs) based on a half-ring (40-60-µm-diameter) depressed-index cladding (type III) geometry are fabricated in monoclinic Tm³⁺:MgWO₄ by femtosecond (fs) laser writing at a repetition rate of 1 kHz. The WGs are characterized by confocal laser microscopy and μ-Raman spectroscopy. A Tm³⁺:MgWO₄ WG laser generates 320 mW at ∼2.02µm with a slope efficiency of 64.4%. The WG emits a transverse single-mode and linear polarization (E||N_m). A remarkable low loss of <0.1dB/cm is measured for the WG. Vibronic laser emission at ∼2.08µm is also achieved.