NPGS : Dammann Grating
This is an optical photo of one corner of a Dammann grating written in PMMA. The grating consists of 8x8 units cells, where each cell is 100 um square. The image is approximately 2.5 cells wide. The slightly darker areas were exposed by the beam (making a checker board pattern). The smallest features are the small squares which are 5.1 um on a side. Optical studies of the pattern show that the pattern itself has excellent resolution with near perfect uniformity.
This pattern was exposed on an insulating substrate where a top layer of ~10 nm of Al was evaporated before the exposure to eliminate writing distortions from charging. Before development of the PMMA, the Al was etched off in a solution of NaOH.