Sensing fabrication errors in diffraction gratings using high dynamic range imaging.

We describe the design of a simple instrument for the identification and characterization of fabrication errors in diffraction gratings. The instrument uses an uncooled charge-coupled device (CCD) camera and a high dynamic range imaging process to detect the light scattered off a grating under test in the focal plane of a lens. We demonstrate that the instrument can achieve a dynamic range around nine orders of magnitude and we show that we are able to clearly identify small, periodic fabrication errors in two test gratings that could not be detected with microscopic techniques.