Par Paul Deba - 28/04/2010
Address : Laboratoire d’ Astrophysique de Toulouse-Tarbes
. . . . . . . : 14 Av. Edouard Belin
. . . . . . . : 31400 Toulouse - France
. . . . . . . : Observatoire Midi-Pyrénées - Université de Toulouse
Office : RDC
Phone : (+33) 5 61 33 28 21
Fax : (+33) 5 61 33 28 40
Email : paul.deba at ast.obs-mip.fr
- Research and Technology actions about diffractive membrane space telescopes, namely Fresnel Diffractive Array Imagers (FDAI). Small size, ground-based FDAI prototypes have been engineered, built and integrated in order to assess their optical performances and validate such an optical scheme with a view to space missions by 2020-2025 horizon [Koechlin et al., Experimental Astronomy, 2005]. Technology Readiness Level 04 is aimed.
- R&T CNES 2004-2007 : 80-mm aperture generation I prototype, set up in cleanroom at C.E.S.R. → corroborated the concept in visible range (0.45 < λ < 0.65) μm on artificial targets. [Serre Ph.D.] [Serre et al., Applied Optics, 2009]
- R&T CNES 2008-2010 : 200-mm aperture generation II prototype attached along the Bischoffscheim refractor tube in Nice Observatory (O.C.A.) → Successful validation on real sky targets (angular resolution, dynamic range, sensitivity) for VIS - near IR (0.6 < λ < 0.9) μm. [Koechlin 2010]
- RTRA-STAE supports 2009-2011 FDAI-UV project : a 70-mm aperture generation III prototype is being designed and implemented to prove FDAI feasibility in the Ultra-Violet waveband, with reflecting-only optical surfaces making up the Receiver module.
- Involved in the phase zero study lead by CNES (2008-2010) about space FDAIs including the optical scenarios layout of Fresnel array and Receiver optics spacecrafts, the GNC strategies of the formation flying.
- Binary diffractive Optics :
200 mm square binary Fresnel arrays have been carved into thin substrates : copper-beryllium foil (e=50 μm), polyimide foil (e=100 μm)... Light is focused at order +1 of diffraction by many thousands void subapertures : home-made softwares compute their vectorized specifications and generate a toolpath file (Excellon-like). Then, a local company, Micro Usinage Laser, cut the toolpath patterns using a UV laser machine. Count with 250000 closed paths for a 200x200 mm foil that take till ~30 hours machining.
- Blazed diffractive Optics :
- By transmission → Fresnel lenses with co-phased zones, engraved into Silica discs. The latest made features kmax = 702 Fresnel zones, Φ = 58 mm, H = 1.7 μm zone transition height for blaze at λc = 800 nm. Manufactured by SILIOS technology (photolithography + ion etching process)
- By reflection → Concave diffractive Fresnel mirrors. This technology is under development for high quality imagery in the Ultra-Violet wavelengths and represents the core of FDAI-UV project.
- Classical Optics : mirror combinations, dichroic beamsplitter, achromatic doublet...
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