Generation of microstripe cylindrical and toroidal mirrors by localized laser evaporation of fused silica

We report a new technique for the rapid fabrication of micro-stripe cylindrical and toroidal mirrors with a high ratio (> 10) of the two principal radii of curvatures (RoC1/RoC2), and demonstrate their effectiveness as mode-selecting resonator mirrors for high power planar waveguide lasers. In this process, the larger radius of curvature (RoC1) is determined by the planar or cylindrical shape of the fused silica substrate selected for laser processing, whilst the other (RoC2) is produced by controlled CO2 laser-induced vaporization of the glass. The narrow stripe mirror aperture is achieved by applying a set of partially-overlapped laser scans, with the incident laser power, the number of laser scans and their spacing being used to control the curvature produced by laser evaporation. In this work, a 1 mm diameter laser spot is used to produce grooves of cylindrical/toroidal shape with 240 µm width and 16 mm length. After high reflectance coating, these grooves are found to provide excellent mode selectivity as resonator mirrors for a 150 µm core Yb:YAG planar waveguide laser, producing high brightness output at more than 300 W. The results show clearly that the laser-generated micro-stripe mirrors can improve the optical performance of high power planar waveguide lasers when applied in a low-loss mode-selective resonator configuration.