Measurements of heat flow from surface defects in lithium triborate.

We present what is, to our knowledge, the first measurement of temperature distributions in a nonlinear optic resulting from absorption in a localized surface defect. These measurements were performed on principal cut samples of lithium triborate with damage spots centered on their front surfaces, pumped by a kW-scale continuous-wave laser. The changes in optical-path length associated with this heating were measured with a Mach-Zehnder interferometer, from which the temperature distribution could be inferred. These distributions have sharper features with larger magnitudes than would be expected with bulk-absorption heating. Comparison with both numerical and analytical models is used to qualify the measurements and to estimate the total power absorbed at a given site using this bulk material response. While sensitivity is dependent on the properties of the material of study, we demonstrate measurements of absorption levels of one part in 10