Scatter properties of polycrystalline YAG in the visible and near-infrared

Yttrium Aluminum Garnet (YAG) is an important laser host material. Ideal host materials have low loss at the laser transition frequency. This becomes more important as the gain length increases or a low gain transition is of interest. Unfortunately, single crystal YAG suffers from relatively high scatter caused by strain induced index of refraction variations generated by the growth method. For this reason polycrystalline YAG has been developed with virtually no strain. Furthermore, this material can be doped with concentrations that vary spatially. This can provide a tremendous advantage in matching the gain volume to the mode volume in a laser. However, because of the grain boundaries and porosity, polycrystalline materials have scatter loss. Angle resolved, in-plane scatter measurements of polycrystalline YAG and Nd: YAG are reported from 405 to 1064 nm. This covers the range of interest for laser operation but also with enough bandwidth to derive a physical understanding of the scatter mechanisms. A model is also applied to provide physical insight and interpolation and meaningful extrapolation of the experimental results.