PLANAR YAG/Yb:YAG/YAG WAVEGUIDES FABRICATED VIA TAPE CASTING: PREPARATION, MICROSTRUCTURE AND LASER EMISSION CHARACTERIZATION

Optical planar waveguides provide an alternative approach to free propagation in bulk materials for the realization of high power laser devices. In the case of solid state lasers pumped by highly divergent semiconductor lasers, guiding the pump beam allows to maintain high pump intensities in the active media over longer absorption lengths than those possible by free propagation. This in turn can provide advantages for the thermal dissipation of the pumped region. Ceramic fabrication processes can be successfully exploited for the realization of planar waveguides. Here we report the fabrication and the laser operation of a planar YAG/Yb:YAG/YAG waveguide fabricated by non-acqueous tape casting, already exploited for the preparation of multilayer Yb:YAG structures [1]. Two mixtures were prepared from commercial oxide powders: one with the stoichiometry of YAG and the other 20% Yb:YAG. The layered structure of the waveguide was prepared by the stacking of raw tapes, which were consequently compressed at elevated temperature into one piece. The ceramics were sintered under high vacuum and annealed in air. The 100 µm thick Yb doped layer sustains both the laser action, and the multimode wave guiding, due to its refractive index, higher than the undoped YAG substrate (estimated difference +.003 [2])..The waveguide, with a length of 8 mm, was end pumped in the guiding layer with a fiber coupled diode laser emitting at 968 nm, and inserted in a confocal cavity. The cavity is designed so that the fundamental mode cavity mode experiences free propagation in the doped layer, whereas the propagation of the pump beam is affected by the guiding action. Laser emission was obtained in quasi CW pumping regime, at a wavelength of 1029 nm, with a maximum slope efficiency of about 30% with respect to the absorbed pump power, and a maximum output power of 3.4 W.