Pump coupling optimization of a native inhomogeneous planar waveguide laser

Planar waveguide laser is a promising candidate for high power solid state lasers. Normally the native inhomogeneous refractive index exists during fabrication process, this will apparently affect power scaling and beam quality. Few quantitative works have been reported to the optimization of this behavior and in practice, try and error routine is needed to set pump conditions. In this work, we manufactured a miniature composite Yb:YAG ceramic waveguide laser via non-aqueous tape casting method, refractivity index gradience is natively generated via border diffusion between the Yb:YAG and YAG layers. We found a simple and effective criterion to treat pump optimization by combining wave optics model and laser rate equations. Guided by this criterion, we obtained an experimental slope-efficiency about 66% with optimized pumping beam parameters. This method could be forward applied in similar designs and much higher power planar waveguide lasers.