The measurement of energy deposited in optical coatings on windows or mirrors is necessary for the non-destructive estimation of damaae thresholds which are of particular significance in laser optics. Such measurements are very difficult to perform by observing energy loss from a light beam incident on the optical element, since the absorbed energy is very low (ppm range) and at these levels absorption and scattering of the light are difficult to quantify separately. The technique described below offers a sensitive, non-invasive approach to calculating peak temperatures reached at the surface of the element under pulsed conditions. Results are reported for a variety of mirror surfaces and substrates.