Hybrid or Monolithic ? Pixel detectors for future LHC experiments
Complete Characterization of sub-pixel Response of Near-Infrared Detectors ( Spot s -O-Matic )
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Transcript of Complete Characterization of sub-pixel Response of Near-Infrared Detectors ( Spot s -O-Matic )
October 14, 2009 Detectors for Astronomy, Garching
Complete Characterization of sub-pixel Response of Near-Infrared Detectors (Spots-O-Matic)Tomasz Biesiadzinski, Greg Tarlé, Michael Howe, Curtis
Weaverdyck, Michael Schubnell, Wolfgang Lorenzon
October 14, 2009 Detectors for Astronomy, Garching
Outline Why do we care about sub-pixel response? The Spot-O-Matic
Our first look at intra-pixel response Barron et al., “Subpixel Response Measurement of Near-Infrared
Detectors”, PASP (2007) Spots-O-Matic
Concept Effects of sub-pixel structure
Simulation of errors on point source photometry and simulated Spots-O-Matic correction
Weak lensing considerations Possible errors Shape projection capabilities
Spots-O-Matic Progress Lens characterization
October 14, 2009 Detectors for Astronomy, Garching
Under-sampling for Survey Telescopes
Modern survey telescopes employ under-sampling to improve survey speed. Precision photometry or galaxy shape measurements (for Weak Lensing) in
under-sampled telescopes requires dithering and/or well-characterized intra-pixel response.
For under-sampled NIR survey telescopes, sub-pixel detector properties become important Charge Diffusion (~1.87m) Capacitive Coupling (~2%) Sub-pixel structure (pixel geometry, defects…)
Well SampledUnder-sampled (Assuming Perfect Pixel)
October 14, 2009 Detectors for Astronomy, Garching
Looking Inside a Pixel - the Pixel Response Function (PRF) as measured by the Spot-O-Matic
Single ~1 m spot projector (Spot-o-Matic)
2 dimensional scan over several pixels mapping the internal response
Objective: Determine the largest plate scale a telescope can have while still delivering 1% photometric precision for point sources (e.g. SNe).H2RG-102 one dimensional scan (and
fit to data points) showing effects of charge diffusion and capacitive coupling
October 14, 2009 Detectors for Astronomy, Garching
Spot-O-Matic Results
For detectors with high quantum efficiency, better than 1% photometry is achieved with PSF’s > ½ the size of a pixel
Note small random defects (~5%) that could affect galaxy shape reconstruction for weak lensing.
2 dimensional scan of an individual pixel response
Summation over multiple pixels showing uniform photometry
October 14, 2009 Detectors for Astronomy, Garching
Spots-O-MaticConcept
Simultaneously scan anarray of 160000 spots (400 x 400) to rapidly characterize the sub-pixel response of an entire detector Standard 17.5 cm x 17.5cm
photolithography mask Illuminated by NIR laser Each spot scans a 5 by 5 pixel array
6 axis computer controlled stage X and Y axis to perform a 2D scan of the entire detector Z axis to sample focal “plane” over depth of focus tip, tilt, rotation stages to make sure the image and detector are co-planar and scan is
aligned with rows/columns Use a commercial 50mm lens to demagnify and focus the image
Zeiss Planar T* 1.4/50ZF IR, optimized for NIR light (optics, AR coatings) 28 cm object distance, 6.2 cm image distance, -1/4.5 magnification Cold laser line filter inside dewar blocks out-of-band light
October 14, 2009 Detectors for Astronomy, Garching
Simulation of the use the Spots-o-Matic to Improve Photometry Simulated Spots-o-
Matic signal obtained by convolving Spot-o-Matic Scan with 6m PSF
October 14, 2009 Detectors for Astronomy, Garching
Point Source Photometry (SNe) withoutSpots-o-Matic correction
All fitted fluxes are within ±0.3% of the true values
3.6% of SNe have fluxes with more than 1% error 0.4% of SN have fluxes with
more than 2% error
Large plate Scale 0.81 arcsec/pixel = 0.11 Pixels
Small plate scale 0.23 arcsec/pixel = 0.39 Pixels
October 14, 2009 Detectors for Astronomy, Garching
Errors are now at the sub 0.1% level
All fitted fluxes are within ±0.2% of the true values
Point Source Photometry (SNe) withSpots-o-Matic correction
Large plate Scale 0.81 arcsec/pixel = 0.11 Pixels
Small plate scale 0.23 arcsec/pixel = 0.39 Pixels
October 14, 2009 Detectors for Astronomy, Garching
Spots-O-Matic & Weak Lensing Dithering
Reconstructs diffraction limited seeing in under-sampled telescopes at the expense of survey speed
Compensates for intrapixel structure A complete Spots-o-Matic scan can reduce the number of
dithers required to achieve a given level of shape discrimination
Simulations have yet to be performed to quantify this Can large plate scale HgCdTe detectors be used for
shape reconstruction? Spots-o-Matic data will provide the answer Elliptical “galaxies” and point sources (PSF calibration
“stars”) will be projected onto real detectors and shapes will be extracted
Sub-pixel features mapped by the Spots-O-Matic will be used to correct the shapes for known intrapixel response and determine the errors after correction
October 14, 2009 Detectors for Astronomy, Garching
Spots-O-Matic Lens Characterization Questions
Can a lens produce small enough spots? What is the f-stop that results in minimum
spot size? Lens quality vs. diffraction limit How does the spot size change with
location in the field of view? Knife edge technique
Scaned the spot repeatedly across a knife edge1 (razor blade) while focusing in z.
The spatial derivative of the signal at best focus gives a one dimensional profile of the lens PSF
1Firester, A. H., Heller, M. E., & Sheng, P. 1977, Appl. Opt., 16, 1971
October 14, 2009 Detectors for Astronomy, Garching
Lens Characterization RunsFocusing in Z AxisRaw Signal
Obtained Scans at f / # 5.6, 2.8 and 1.4 on lens axis
At f / # 5.6, 7.5 cm off axis Planned Spots-O-Matic mask range
October 14, 2009 Detectors for Astronomy, Garching
Measured PSF’s of the Lens at Different F-stops
October 14, 2009 Detectors for Astronomy, Garching
Lens Characterization Results Obtained spot sizes (Demagnified by
factor of 4.5): f / # 1.4: on axis
FWHM = 5.4 m Fitted = 6.6 m
f / # 2.8: on axis FWHM = 4.7 m Fitted = 2.9 m
f / # 5.6: on axis FWHM = 5.8 m Fitted = 2.8 m
f / # 5.6: off axis Fitted = 3.4 m
Manufacturer indicated diffraction limited psf at f/# 5.6 Complicated structure at lower f-stops likely due to lens defects Can’t measure FWHM in the off-axis scan (due to low signal to noise) but the fit
indicates ~17% deterioration of from on axis Plan to scan at f/# 2.8 which appears to be a better choice for the Spots-O-Matic Spots-o-Matic spot size will be m (as determined by fwhm/2.35)
October 14, 2009 Detectors for Astronomy, Garching
Conclusion The Spots-O-Matic will provide ~ 2 m resolution
scans of an entire HgCdTe detector in ~ 1 day. With a standard lens it can be used on visible CCDs with
likely better resolution The spot size is not significantly degraded at the
periphery of the field of view Now that we have characterized the optics we are
proceeding with final design and construction of the Spots-o-Matic.
We expect first scans by Spring 2010 in time to influence JDEM instrument design.