Scattered Light in a DMD based Multi-Object Spectrometer
2010
The DMD (Digital Micromirror Device) has an important future in both ground and space based multi-object
spectrometers. A series of laboratory measurements have been performed to determine the scattered light properties of a
DMD. The DMD under test had a 17 μm pitch and 1 μm gap between adjacent mirrors. Prior characterization of this
device has focused on its use in DLP (TI Digital Light Processing) projector applications in which a whole pixel is
illuminated by a uniform collimated source. The purpose of performing these measurements is to determine the limiting
signal to noise ratio when utilizing the DMD as a slit mask in a spectrometer. The DMD pixel was determined to scatter
more around the pixel edge and central via, indicating the importance of matching the telescope point spread function to
the DMD. Also, the generation of DMD tested here was determined to have a significant mirror curvature. A maximum
contrast ratio was determined at several wavelengths. Further measurements are underway on a newer generation DMD
device, which has a smaller mirror pitch and likely different scatter characteristics. A previously constructed instrument,
RITMOS (RIT Multi-Object Spectrometer) will be used to validate these scatter models and signal to noise ratio
predications through imaging a star field.
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