Recognition of damage in polarizing transmission-grating facets.

An optical setup was built for microscopic damage inspection on transmission-grating facets composed of a gold-wire structure. Contrast improvement was achieved by exploiting the polarizing properties of these gratings in the near-infrared region. Spatial filtering yields an additional contrast enhancement and reduces unwanted signals caused by the periodic support structure. An image-processing algorithm is developed that evaluates the number and the size of the faults in a grating facet with high accuracy from only one digital image.