Subsurface damage control and measurement is critical on a wide range of optical elements. The amount of subsurface damage present in an optic determines its yield strength, the amount of laser power that the optic can handle, and the flatness that can be maintained during the coating process. In these days of reduced tolerance for mission failure, it is critical to have accurate knowledge of the condition of an optic before sending it into space. Destructive tests provide very accurate measurements of subsurface damage, but such testing can be time consuming and an uncertainty always remains: Does the finished part have the same subsurface properties as the measured sample? Various laser scattering techniques currently provide non-destructive measurement of subsurface measurement, but these measurements are all indirect. The laser scattering techniques directly measure the amount of laser light scattered from a surface and below, which is then correlated to an approximate depth of subsurface damage that might produce the measured amount of scattering. In contrast, the technique presented here is both a non-destructive and direct measurement of the depth and extent of subsurface damage. Because it is a direct measurement, subsurface damage depth can be reported in real time, allowing for in-process corrections and optimizations. This paper presents the measurement setup and offers an example of the experimental output provided by this new method.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.