A scanning darkfield laser scatterometer is used to produce maps of surface defects on optical component surfaces. This instrument was originally developed for the examination of silicon wafers. The short depth of filed, high resolution darkfield imaging design of the scattering measurement head, enables the instrument to examine the cleanliness and surface condition of transparent as well as opaque optical surfaces, including coated surfaces.

The measurement system consists of a laser illuminated darkfield optical head mounted on a linear translation stage, a spinning chuck, and a data acquisition and display system. The instrument is capable of resolving the ac scattered light component to two parts in 10⁹ for scattering sites smaller than the pixel size (50 microns). The dc sensitivity of the instrument is roughly one part in 10⁶ (1 ppm).

The instrument has been successfully used in inspecting mirror substrates before and after coating and in developing cleaning techniques. Operation of the system and some data will be presented.