UV-Deflectometry: No parasitic reflections

Phase Measuring Deflectometry (PMD) is an established method to measure specular freeform surfaces such as eyeglass lenses. For transparent objects however, parasitic reflections originating from the rear side of the specimen currently render an examination without specific preparation impossible. Whereas a purely algorithmic approach will be presented elsewhere at this conference, we will demonstrate a hardware solution based on ultraviolet illumination. As most specimens of interest are not transparent in the ultraviolet regime, no parasitic reflections occur. So far, this idea has only been presented in a theoretical way due to a practical problem: How to achieve the required illumination pattern without an expensive ultraviolet projection system? In this contribution we present a novel concept and first experimental results using a quartz mask with a grid composed of multiple Gaussian lines. For each line the desired intensity distribution is accomplished by a suitable dithering structure. The whole device is illuminated from behind and moved laterally. We minimized the required motion range by an optimized layout of the grid.