Thermo-optic quality assessment of doped optical ceramics

The use of optical quality ceramics for laser applications is expanding, and with this expansion there is an increasing need for diagnostics to assess the quality of these materials. Ceramic material with flaws and contaminants yields significantly less efficient performance as laser gain media and can generate excessive amounts of waste heat. This is a concern that is especially relevant in high power laser applications where thermally induced damage can be catastrophic. In order to assess a set of ceramic and crystalline samples we induce and measure thermal lensing in order to produce a relative ranking based on the extent of the induced thermal lens. In these experiments thermal lensing is induced in a set of nine 10% Yb:YAG ceramic and single-crystal samples using a high power 940 nm diode, and their thermal response is measured using a Shack-Hartmann wavefront sensor. The materials are also ranked by their transmission in the visible region. Discrepancies between the two ranking methods reveal that transmission in the visible region alone is not adequate for an assessment of the overall quality of ceramic samples. The thermal lensing diagnostic technique proves to be a reliable and quick over-all assessment method of doped ceramic materials without requiring any a priori knowledge of material properties.