MEMS-based Spectrogra phs P. Spanò INAF Osservatorio Astronomico di Brera, ITALY Recent Advances on their Optical Design STScI, Baltimore June 25, 2010
MEMS-based Spectrographs P. Spanò INAF Osservatorio Astronomico di Brera, ITALY Recent Advances on their Optical Design STScI, Baltimore June 25, 2010.
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MEMS-based Spectrograp
hs
P. Spanò INAF
Osservatorio Astronomico di Brera, ITALY
Recent Advances on
their Optical Design
STScI, BaltimoreJune 25, 2010
MEMS-based Spectrographs: Advances on their Optical Design
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INAF & O.A.Brera
Since 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, 2010
Merate Observatory
STScI Baltimore June 25, 2010
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MEMS-based Spectrographs: Advances on their Optical Design
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We, GOLEM (Gruppo Ottiche e LEnti Merate) are a small team of astronomers and engineers located in Merate
We 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 wavelengths
More recently, we were involved in space-based projects, like SPACE (now EUCLID)
From ground to SPACE
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SPACE
STScI Baltimore June 25, 2010
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ESA led a study to merge together the two Dark Energy missions, SPACE and DUNE into EUCLID
Weak-lensing and BAOs as probes for DE
1.2m shared telescope
VIS + NIR photometry
NIR spectroscopy
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Digital Micromirror Devices
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DMD principles - I
DMD 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° angle
DMD surface
DMD micromirror
ON: +12°
OFF: -12°
Incident ray
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DMD principles - II
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DMD principles - III
Tilt 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
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DMD illumination geometry - I
Rotation axis of the DMD mirror
45°
45°
Reflected ray
DMD area
DMD micromirror
DMD normal
0° 24°(angle w.r.t. DMD normal)
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DMD illumination geometry - II
4º
28º
23º
23º
17.9º
24º
Minimum and maximum
Equal amplitude One perpendicular to field
4º
20º
16.73º
16.73º
24º
17.9º
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RITMOS (Meyer et al. 2004)
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F/8 beam
0.8” micromirrors (@Mees 0.6m tel.)
11’x8’ FoV (@Mees 0.6m tel.)
0.39-0.49 um
R=6000
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IRMOS(MacKenty et al. 2004)
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F/5.6 beam
17um micromirrors (=0.2”@KPNO 4m)
3’x2’ FoV (@KPNO 4m)
0.85-2.5 um (ZJHK)
R=300-3000
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SPACE DMD-baseline(Content et al., Durham Univ.)
F/2.2 beam
14um micromirrors (=1” @ 1.2m)
49’x34’ FoV
0.9-1.7 um
R=400
Very complex mirrors, large & heavy, complex mechanisms
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SPACE DMD altenative I(by Grange et al., Lab. Astroph. Marseille)
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F/2.7 beam
14um micromirrors (=0.9” @ 1.2m)
26’x14’ FoV
1.0-1.7 um
R=400
Simpler, smaller, reduced performances
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SPACE DMD altenative II(by Spanò et al., INAF)
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F/4 beam
14um micromirrors (=0.6” @ 1.2m)
20’x11’ FoV
0.9-1.75 um
R=400
Very compact, small field
50cm
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TIR prisms
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TIR on beamers
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Beamer Requirements
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Example of TIR image quality
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(Bow
ron,
et
al. S
PIE
5186,2
003)
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DMD @ Galileo Telescope
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A simplified approach
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Modular design, simple layout, cheap optics
Low resolution
“Large” field of view
High efficiency
“Off-the-shelf” optics
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The starting idea(Zamkotsian et al., ASP Conf. 207, 2000)
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F/7 beam
Proposed for NIRMOS
Two spherical mirrors and a convex spherical grating
1:1 Offner-like design
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The design
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Two arms: Spectro & Imaging
Wavelengths: 400-800 nm
Spectral resolution: 250
Focal ratio: F/4
FoV: 4.5’x7’
Detectors: 2kx2k (spect.), 1kx1k (imaging)
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Optical Design
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Optical details
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Slits and spectra
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Mechanical layout
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Summary DMD spectrographs with enhanced FoV can be
designed with faster beams
TIR prisms can be very effective to keep size very small
Simpler designs if Offner-type configurations are selected
STScI Baltimore June 25, 2010
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