Characterization of MOEMS devices for the instrumentation of next generation space telescope

Instrumentation of the Next Generation Space Telescope (NGST) will include a Multi-Object Spectrograph (MOS) in order to record simultaneously several hundred spectra in a single observation run. The selection of the objects in the field of view will be done by a MOEMS-based device: a micro-shutter array (MSA). In Laboratoire d'Astrophysique de Marseille, we have developed since several years different tools for the modeling and the characterization of these MOEMS-based slit masks. We are now developing a new bench for the measurement of the contrast value. The contrast is the amount of non-selected flux from sky background and bright sources passing through the multi-slit device. Contrast measurement have been carried out on the micro-mirror array fabricated by Texas Instrument. We can address several parameters in our experiment, as the size of the source, its location with respect to the micro-elements, the wavelength, and the input and output pupil size. In order to measure the contrast, the micro-mirrors are tilted between the ON position (towards the spectrograph) and the OFF position (towards a light trap). Contrast exceeding 400 has been measured for a 10° ON/OFF angle and values exceeding 6000 for a 20° ON/OFF angle.