DMD @ TNG

MEMS-based SpectrographsP. Span INAF Osservatorio Astronomico di Brera, ITALY

Recent Advances on their Optical Design

STScI, BaltimoreJune 25, 2010INAF & O.A.BreraSince 2003 O.A.Brera is one of the 19 institutes currently part of the Instituto Nazionale di Astrofisica (INAF)

12 Observatories and 7 Institutes former belonging to the National Research Council (CNR)

STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design2

Merate ObservatorySTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design3

STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design4We, GOLEM (Gruppo Ottiche e LEnti Merate) are a small team of astronomers and engineers located in MerateWe works mainly for ground-based telescopes (e.g., the GRB shooter REM in La Silla, Chile) and focal plane instrumentation (e.g., X-shooter on ESO VLT in Paranal, Chile, again) for optical-to-NIR wavelengthsMore recently, we were involved in space-based projects, like SPACE (now EUCLID)From ground to SPACESPACESTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design5

STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design6

ESA led a study to merge together the two Dark Energy missions, SPACE and DUNE into EUCLIDWeak-lensing and BAOs as probes for DE1.2m shared telescopeVIS + NIR photometryNIR spectroscopyDigital Micromirror DevicesSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design7

STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design8DMD principles - IDMD micromirror can tilt (along its diagonal) by +/- 12 deg (in the Cinema DLP)

They correspond to two different states: On and Off

A third state (power off) exists, with a 0 angleDMD surfaceDMD micromirrorON: +12OFF: -12Incident rayDMD principles - IISTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design9

STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design10DMD principles - IIITilt happens along the diagonal of the micromirror, so a 45 deg rotation of the device is required to keep chief rays within a plane perpendicular to the DMD surface

STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design11DMD illumination geometry - IRotation axis of the DMD mirror4545Reflected rayDMD areaDMD micromirrorDMD normal024(angle w.r.t. DMD normal)STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design12DMD illumination geometry - II428232317.924Minimum and maximumEqual amplitudeOne perpendicular to field42016.7316.732417.9RITMOS (Meyer et al. 2004)STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design13

F/8 beam0.8 micromirrors (@Mees 0.6m tel.)11x8 FoV (@Mees 0.6m tel.)0.39-0.49 umR=6000

IRMOS(MacKenty et al. 2004)STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design14F/5.6 beam17um micromirrors (=0.2@KPNO 4m)3x2 FoV (@KPNO 4m)0.85-2.5 um (ZJHK)R=300-3000

STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design15SPACE DMD-baseline(Content et al., Durham Univ.)F/2.2 beam14um micromirrors (=1 @ 1.2m)49x34 FoV0.9-1.7 umR=400Very complex mirrors, large & heavy, complex mechanisms

SPACE DMD altenative I(by Grange et al., Lab. Astroph. Marseille)STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design16

F/2.7 beam14um micromirrors (=0.9 @ 1.2m)26x14 FoV1.0-1.7 umR=400Simpler, smaller, reduced performancesSPACE DMD altenative II(by Span et al., INAF)STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design17F/4 beam14um micromirrors (=0.6 @ 1.2m)20x11 FoV0.9-1.75 umR=400Very compact, small field

50cmTIR prismsSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design18

TIR on beamersSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design19

Beamer RequirementsSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design20

Example of TIR image qualitySTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design21

(Bowron, et al. SPIE 5186,2003)DMD @ Galileo TelescopeSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design22

A simplified approachSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design23Modular design, simple layout, cheap opticsLow resolutionLarge field of viewHigh efficiencyOff-the-shelf opticsThe starting idea(Zamkotsian et al., ASP Conf. 207, 2000)STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design24

F/7 beamProposed for NIRMOSTwo spherical mirrors and a convex spherical grating1:1 Offner-like designThe designSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design25

Two arms: Spectro & ImagingWavelengths: 400-800 nmSpectral resolution: 250Focal ratio: F/4FoV: 4.5x7Detectors: 2kx2k (spect.), 1kx1k (imaging)Optical DesignSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design26

Optical detailsSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design27

Slits and spectraSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design28

Mechanical layoutSTScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design29

SummaryDMD spectrographs with enhanced FoV can be designed with faster beamsTIR prisms can be very effective to keep size very smallSimpler designs if Offner-type configurations are selected

STScI Baltimore June 25, 2010MEMS-based Spectrographs: Advances on their Optical Design30