Complete Characterization of sub-pixel Response of Near-Infrared Detectors Spots-O-Matic

1. October 14, 2009 Detectors for Astronomy, Garching Complete Characterization of sub-pixel Response of Near-Infrared Detectors (Spots-O-Matic) Tomasz Biesiadzinski, Greg Tarl�, Michael Howe, Curtis Weaverdyck, Michael Schubnell, Wolfgang Lorenzon

2. 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

3. 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 (~1.87mm) Capacitive Coupling (~2%) Sub-pixel structure (pixel geometry, defects�)

4. 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 mm 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).

5. 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 > � the size of a pixel Note small random defects (~5%) that could affect galaxy shape reconstruction for weak lensing. If there was signal being lost at the edge of the pixels there would have been gutters. It took several days to obtain the scan that you see here using the spot-o-matic. wouldn�t it be wonderfull if�If there was signal being lost at the edge of the pixels there would have been gutters. It took several days to obtain the scan that you see here using the spot-o-matic. wouldn�t it be wonderfull if�

6. October 14, 2009 Detectors for Astronomy, Garching Spots-O-MaticConcept Simultaneously scan an array 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

7. 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 6mm PSF assume this is represenatative of the entire detecto. Can use this to create more realistic PSF models as a function of position within a pixelassume this is represenatative of the entire detecto. Can use this to create more realistic PSF models as a function of position within a pixel

8. October 14, 2009 Detectors for Astronomy, Garching Point Source Photometry (SNe) withoutSpots-o-Matic correction Picked this plate scales since it was considered for JDEM. While very large plate scales are possible while keeping good photometric precision, upper limits do exits. These limits can be raised with the spots-o-matic.Picked this plate scales since it was considered for JDEM. While very large plate scales are possible while keeping good photometric precision, upper limits do exits. These limits can be raised with the spots-o-matic.

9. October 14, 2009 Detectors for Astronomy, Garching You can apparently use large plate scale for point sources but it�s unlikely it will be that good for weak lensingYou can apparently use large plate scale for point sources but it�s unlikely it will be that good for weak lensing

10. 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 space is an ideal environment for weak lensing because of the stability of the psf after first bullet Many of the concepts currently under consideration for JDEM utilize NIR pixels with large plate scale for a weak lensing survey. It is not clear at this time if such an approach can be successfully employed A deeper question is if it�s even possible to do weak lensing with such large plate scales and with NIR detectorsspace is an ideal environment for weak lensing because of the stability of the psf after first bullet Many of the concepts currently under consideration for JDEM utilize NIR pixels with large plate scale for a weak lensing survey. It is not clear at this time if such an approach can be successfully employed A deeper question is if it�s even possible to do weak lensing with such large plate scales and with NIR detectors

11. October 14, 2009 Detectors for Astronomy, Garching 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 What we�ve done so far is the first step in the pocess to produce a working spots-o-matic; we�ve characterized the optics same knife edge technique that was used for the spot-o-maticWhat we�ve done so far is the first step in the pocess to produce a working spots-o-matic; we�ve characterized the optics same knife edge technique that was used for the spot-o-matic

12. October 14, 2009 Detectors for Astronomy, Garching Lens Characterization Runs raw signal near best focus put an arrow to indicate best focusraw signal near best focus put an arrow to indicate best focus

13. October 14, 2009 Detectors for Astronomy, Garching Measured PSF�s of the Lens at Different F-stops

14. 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 mm Fitted s = 6.6 mm f / # 2.8: on axis FWHM = 4.7 mm Fitted s = 2.9 mm f / # 5.6: on axis FWHM = 5.8 mm Fitted s = 2.8 mm f / # 5.6: off axis Fitted s = 3.4 mm The distortions due to the figure of the lens do not compete with the diffraction limit at f 5.6 Size of the spot continues to decrease down to f 2.8The distortions due to the figure of the lens do not compete with the diffraction limit at f 5.6 Size of the spot continues to decrease down to f 2.8

15. October 14, 2009 Detectors for Astronomy, Garching Conclusion The Spots-O-Matic will provide ? ~ 2 mm 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.