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||Nm). A remarkable low loss of <0.1dB/cm is measured for the WG. Vibronic laser emission at ∼2.08µm is also achieved.

Ultrafast laser inscribed waveguide lasers in Tm:CALGO with depressed-index cladding.

Depressed-index buried and surface channel waveguides (type III) are produced in a bulk 3.5 at.% Tm3+:CALGO crystal by femtosecond direct-laser-writing at kHz repetition rate. The waveguides are characterized by confocal microscopy and µ-Raman spectroscopy. Under in-band-pumping at 1679 nm (3H6 → 3F4 transition) by a Raman fiber laser, the buried channel waveguide laser with a circular cladding (diameter: 60 µm) generated a continuous-wave output power of 0.81 W at 1866-1947 nm with a slope efficiency of 71.2% (versus the absorbed pump power) and showed a laser threshold of 200 mW. The waveguide propagation losses were as low as 0.3 ± 0.2 dB/cm. The laser performance under in-band pumping was superior compared pumping at ∼800 nm (3H6 → 3H4 transition), i.e., the convetional pump wavelength. Vibronic laser emission from the WG laser above 2 µm is also achieved. The low-loss behavior, the broadband emission properties and good power scaling capabilities indicate the suitability of Tm3+:CALGO waveguides for mode-locked laser operation at ∼2 µm.