New astronomical instrument using MOEMS-based programmable diffraction gratings

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Programmable Micro-Diffraction Gratings (PMDG) are a new type of MOEMS, opening new observational capabilities in future astronomical instrumentation. Programmable gratings are based on a serial of parallel ribbons able to move out of the plane. By using electrostatic force, ribbons are actuated and a grating could be formed. A few ribbons are efficient enough to diffract the light; then, locally, this grating acts as a ON-OFF switch. If the spectrum is focused on this type of device, by setting ON and OFF a selected number of wavelengths, the spectral response of the spectrograph is programmable. Programmable gratings permit the design of programmable spectrometers, useful in space mission, like ESA Darwin mission. This mission will search, detect and characterize exo-planets, using high-contrast nulling interferometry, coupled with spectroscopic observation. We propose a new observational concept for Darwin using a programmable spectrometer. By tailoring the spectral response, sensitivity as well as signal to noise ratio of the instrument will be increased. A demonstrator breadboard with a PMDG device has been designed and built. This demonstrator, including adjustable sources (location, spectral type, brightness), permits the tailoring of spectral patterns by the PMDG component. Two parallel spectral and imaging channels are used for the optical analysis of the tailored signals. Typical exo-planet spectra have been generated and set by the PMDG. Simulated signatures of exo-planets with life forms are clearly revealed and characterized on the breadboard, demonstrating successfully our concept. Several new observational modes using PMDG devices in future astronomical instrumentation is then foreseen.