Yb:KGd(WO4)2 channel waveguide laser fabricated by ultrafast laser writing

High-power, waveguide-based microchip laser devices designed for integrated optical circuits. Here we report a channel waveguide laser fabricated in a Yb³⁺-doped KGd(WO₄)₂ (Yb:KGdW) crystal using an ultrashort pulse laser inscription technique. The laser beam was circularly polarized and was focused with ax20 microscope objective into the sample 430 mum beneath the surface and the sample was translated with a velocity of 6.0 mm/s. The waveguides were optimized for writing pulse energies of 0.3-0.5 muJ and it was observed that material laser damage arose at pulse energies exceeding ~ 0.35 muJ and additional cracking between the two written lines was evident at energies above 0.37 muJ. For the laser experiments a plane dielectric mirror coated for high transmission at 981 nm and high reflectivity in 1020-1100 nm range and output couplers (T=1%, 3% and 5%) were attached to the end faces of the Yb:KGdW waveguide. The maximum output power of up to 19 mW was produced using 5% output coupling at 1023 nm for 340 mW of pump power. The lasing thresholds were observed to be around 100 mW of incident pump power.