Efficient femtosecond laser written Nd:YAG channel waveguide laser with an output power of more than 1 W

Femtosecond lasers are widely used for three-dimensional volume micro-structuring of dielectric materials. The fabrication of buried channel waveguides inside these materials is interesting especially for the production of passive and active optical devices. The advantages of dielectric waveguide lasers are high optical gain, high damage threshold, and a good overlap between pump mode and laser mode. Neodymium-doped YAG with its high emission cross-section, long fluorescence lifetime, good thermal conductivity, and high mechanical stability is a well suited material for waveguide lasers. This paper reports on stress-induced waveguides which are fabricated using a chirped pulse amplification femtosecond laser system providing laser pulses at a wavelength of 775 nm, a pulse duration of 140 fs, pulse energies up to 1 mJ, and a repetition rate of 1 kHz. Pairs of parallel tracks with a distance of 20 mum to 30 mum are inscribed to the polished surface of Nd:YAG crystal using focused laser pulses with energy of 1muJ. Waveguiding is observed between all written pairs of tracks. Waveguide losses are measured to be as low as 1.4 dB/cm at a wavelength of 1064 nm for pairs of tracks separated by 25 mum. Laser experiments are performed by coupling the light of a Ti: Sapphire laser operating at a wavelength of 808 nm into the waveguide with a lens of 25 mm focal length. The coupling losses are measured to be 30%.