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MEMS-based Spectrographs

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  1. MEMS-basedSpectrographs RecentAdvances on their OpticalDesign P. Spanò INAF Osservatorio Astronomico di Brera, ITALY STScI, Baltimore June 25, 2010

  2. INAF & O.A.Brera • Since 2003 O.A.Brera is one of the 19 institutes currently part of the InstitutoNazionalediAstrofisica (INAF) • 12 “Observatories” and 7 Institutes former belonging to the National Research Council (CNR) MEMS-based Spectrographs: Advances on their Optical Design

  3. Merate Observatory MEMS-based Spectrographs: Advances on their Optical Design

  4. Fromgroundto SPACE • We, GOLEM (Gruppo Ottiche e LEnti Merate) are a small team ofastronomers and engineerslocated in Merate • Weworksmainlyforground-basedtelescopes (e.g., the GRB shooterREM in La Silla, Chile) and focalplaneinstrumentation (e.g., X-shooter on ESO VLT in Paranal, Chile, again) foroptical-to-NIRwavelengths • More recently, wewereinvolved in space-basedprojects, likeSPACE (nowEUCLID) MEMS-based Spectrographs: Advances on their Optical Design

  5. SPACE MEMS-based Spectrographs: Advances on their Optical Design

  6. ESA led a studytomergetogether the two Dark Energy missions, SPACE and DUNE into EUCLID • Weak-lensing and BAOsasprobesfor DE • 1.2m sharedtelescope • VIS + NIR photometry • NIRspectroscopy MEMS-based Spectrographs: Advances on their Optical Design

  7. DigitalMicromirrorDevices MEMS-based Spectrographs: Advances on their Optical Design

  8. DMD principles - I Incidentray • DMD micromirror can tilt (alongitsdiagonal) by +/- 12 deg (in the Cinema DLP) • Theycorrespondtotwodifferentstates: On and Off • A third state (power off) exists, with a 0° angle ON: +12° OFF: -12° DMD micromirror DMD surface MEMS-based Spectrographs: Advances on their Optical Design

  9. DMD principles - II MEMS-based Spectrographs: Advances on their Optical Design

  10. DMD principles - III • Tilt happensalong the diagonalof the micromirror, so a 45 deg rotation of the deviceisrequiredtokeepchiefrayswithin a planeperpendicularto the DMD surface MEMS-based Spectrographs: Advances on their Optical Design

  11. Rotation axis of the DMD mirror Reflected ray 45° 45° DMD area DMD micromirror DMD illuminationgeometry- I 0° 24° (angle w.r.t. DMD normal) DMD normal MEMS-based Spectrographs: Advances on their Optical Design

  12. DMD illuminationgeometry - II 28º 16.73º 24º 16.73º 4º 17.9º 20º 17.9º 23º 24º 4º 23º Minimum and maximum Equal amplitude One perpendicular to field MEMS-based Spectrographs: Advances on their Optical Design

  13. RITMOS (Meyeret al. 2004) • F/8 beam • 0.8” micromirrors (@Mees 0.6m tel.) • 11’x8’ FoV (@Mees 0.6m tel.) • 0.39-0.49um • R=6000 MEMS-based Spectrographs: Advances on their Optical Design

  14. IRMOS(MacKentyet al. 2004) • F/5.6 beam • 17um micromirrors (=0.2”@KPNO 4m) • 3’x2’ FoV(@KPNO 4m) • 0.85-2.5um (ZJHK) • R=300-3000 MEMS-based Spectrographs: Advances on their Optical Design

  15. SPACE DMD-baseline(Contentet al., Durham Univ.) • F/2.2 beam • 14um micromirrors (=1” @ 1.2m) • 49’x34’ FoV • 0.9-1.7um • R=400 • Verycomplexmirrors, large & heavy, complexmechanisms MEMS-based Spectrographs: Advances on their Optical Design

  16. SPACE DMD altenative I(by Grange et al., Lab. Astroph. Marseille) • F/2.7 beam • 14um micromirrors (=0.9” @ 1.2m) • 26’x14’ FoV • 1.0-1.7um • R=400 • Simpler,smaller, reducedperformances MEMS-based Spectrographs: Advances on their Optical Design

  17. SPACE DMD altenative II(by Spanò et al., INAF) • F/4 beam • 14um micromirrors (=0.6” @ 1.2m) • 20’x11’ FoV • 0.9-1.75um • R=400 • Very compact, smallfield 50cm MEMS-based Spectrographs: Advances on their Optical Design

  18. TIR prisms MEMS-based Spectrographs: Advances on their Optical Design

  19. TIR on beamers MEMS-based Spectrographs: Advances on their Optical Design

  20. BeamerRequirements MEMS-based Spectrographs: Advances on their Optical Design

  21. Exampleof TIR imagequality (Bowron, et al. SPIE 5186,2003) MEMS-based Spectrographs: Advances on their Optical Design

  22. DMD @ Galileo Telescope MEMS-based Spectrographs: Advances on their Optical Design

  23. A simplifiedapproach • Modular design, simple layout, cheap optics • Low resolution • “Large” fieldofview • High efficiency • “Off-the-shelf” optics MEMS-based Spectrographs: Advances on their Optical Design

  24. The starting idea(Zamkotsianet al., ASP Conf. 207, 2000) • F/7 beam • Proposedfor NIRMOS • Twosphericalmirrors and a convexsphericalgrating • 1:1Offner-like design MEMS-based Spectrographs: Advances on their Optical Design

  25. The design • Twoarms: Spectro & Imaging • Wavelengths: 400-800 nm • Spectralresolution: 250 • Focalratio: F/4 • FoV: 4.5’x7’ • Detectors: 2kx2k (spect.), 1kx1k (imaging) MEMS-based Spectrographs: Advances on their Optical Design

  26. Optical Design MEMS-based Spectrographs: Advances on their Optical Design

  27. Opticaldetails MEMS-based Spectrographs: Advances on their Optical Design

  28. Slits and spectra MEMS-based Spectrographs: Advances on their Optical Design

  29. Mechanical layout MEMS-based Spectrographs: Advances on their Optical Design

  30. Summary • DMD spectrographswithenhancedFoV can bedesignedwithfasterbeams • TIR prisms can beveryeffectivetokeepsizeverysmall • SimplerdesignsifOffner-typeconfigurations are selected MEMS-based Spectrographs: Advances on their Optical Design