Measuring the flatness of focal plane for very large mosaic CCD camera (original) (raw)
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Measuring the flatness of focal plane for very large mosaic CCD camera
Ground-based and Airborne Instrumentation for Astronomy III, 2010
Large mosaic multiCCD camera is the key instrument for modern digital sky survey. DECam is an extremely red sensitive 520 Megapixel camera designed for the incoming Dark Energy Survey (DES). It is consist of sixty two 4k×2k and twelve 2k×2k 250-micron thick fully-depleted CCDs, with a focal plane of 44 cm in diameter and a field of view of 2.2 square degree. It will be attached to the Blanco 4-meter telescope at CTIO. The DES will cover 5000 square-degrees of the southern galactic cap in 5 color bands (g, r, i, z, Y) in 5 years starting from 2011.
2016
Large mosaic multiCCD camera is the key instrument for modern digital sky survey. DECam is an extremely red sensitive 520 Megapixel camera designed for the incoming Dark Energy Survey (DES). It is consist of sixty two 4k×2k and twelve 2k×2k 250-micron thick fully-depleted CCDs, with a focal plane of 44 cm in diameter and a field of view of 2.2 square degree. It will be attached to the Blanco 4-meter telescope at CTIO. The DES will cover 5000 square-degrees of the southern galactic cap in 5 color bands (g, r, i, z, Y) in 5 years starting from 2011. To achieve the science goal of constraining the Dark Energy evolution, stringent requirements are laid down for the design of DECam. Among them, the flatness of the focal plane needs to be controlled within a 60-micron envelope in order to achieve the specified PSF variation limit. It is very challenging to measure the flatness of the focal plane to such precision when it is placed in a high vacuum dewar at 173 K. We developed two image based techniques to measure the flatness of the focal plane. By imaging a regular grid of dots on the focal plane, the CCD offset along the optical axis is converted to the variation the grid spacings at different positions on the focal plane. After extracting the patterns and comparing the change in spacings, we can measure the flatness to high precision. In method 1, the regular dots are kept in high sub micron precision and cover the whole focal plane. In method 2, no high precision for the grid is required. Instead, we use a precise XY stage moves the pattern across the whole focal plane and comparing the variations of the spacing when it is imaged by different CCDs. Simulation and real measurements show that the two methods work very well for our purpose, and are in good agreement with the direct optical measurements.
Pixel area variation in CCDs and implications for precise photometric calibration
2007 IEEE Nuclear Science Symposium Conference Record, 2007
Images with smooth and moderately flat illumination are commonly used to calibrate pixel to pixel sensitivity variation without consideration that some structure on short spatial scales may be due to reallocation of area between pixels. Errors in the position of pixel boundaries have the effect of repartitioning charge between pixels but do not affect the total charge collected. Since the resulting errors tend to cancel when combining signal from adjacent pixels, this effect has gone largely unnoticed. However proposed wide field astronomical surveys, which strive to achieve high photometric precision with coarse spatial sampling, must take this into account. We present simple analysis techniques to identify how much flat field structure is due to systematic and random variations in pixel area, rather than sensitivity, as a function of row/column direction and spatial frequency. Analysis of data from CCDs made with radically different technologies and pixel sizes by different manufacturers suggests that pixel size variation in the column direction probably dominates QE variations on short spatial scales for all CCDs. Refinements to flat field calibration methods and tests to confirm their efficacy are proposed.
The monitoring of a few critical parameters during epitaxal growth is necessary in order to obtain high quality III-V semiconductor heterostructures. We have developed an electronic circuit that is able to perform realtime analysis of the spatial distribution and intensity of RHEED (reflected high energy electron diffraction) patterns by means of a CCD camera. Besides being used for obtaining information from RHEED patterns, the new system can also be employed for in situ and real time stress measurements during molecular beam epitaxy of lattice mismatched heterostructures. RHEED LASER CELL CELL HEATED WINDOW HEATER MIRROR BEAM-SPLITTER CCD e-GUN SCREEN Fig. 1. Scheme of stress measurement and RHEED systems implemented on the MBE chamber.
Flat-field calibration of CCD detector for long trace profiler
Advances in Metrology for X-Ray and EUV Optics II, 2007
The next generation of synchrotrons and free electron lasers requires x-ray optical systems with extremely highperformance, generally, of diffraction limited quality. Fabrication and use of such optics requires highly accurate metrology. In the present paper, we discuss a way to improve the performance of the Long Trace Profiler (LTP), a slope measuring instrument widely used at synchrotron facilities to characterize x-ray optics at high-spatial-wavelengths from approximately 2 mm to 1 m. One of the major sources of LTP systematic error is the detector. For optimal functionality, the detector has to possess the smallest possible pixel size/spacing, a fast method of shuttering, and minimal nonuniformity of pixel-to-pixel photoresponse. While the first two requirements are determined by choice of detector, the non-uniformity of photoresponse of typical detectors such as CCD cameras is around 2-3%. We describe a flat-field calibration setup specially developed for calibration of CCD camera photo-response and dark current with an accuracy of better than 0.5%. Such accuracy is adequate for use of a camera as a detector for an LTP with performance of ~0.1 microradian (rms). We also present the design details of the calibration system and results of calibration of a DALSA CCD camera used for upgrading our LTP-II instrument at the ALS Optical Metrology Laboratory.
Cryogenic focal plane flatness measurement with optical zone slope tracking
SPIE Proceedings, 2011
We describe a non-contact optical measurement method used to determine the surface flatness of a cryogenic sensor array developed for the JDEM mission. Large focal planes envisioned for future visible to near infra-red astronomical large area point-source surveys such as JDEM, WFIRST, or EUCLID must operate at cryogenic temperatures while maintaining focal plane flatness within a few 10's of μm over half-meter scales. These constraints are imposed by sensitivity conditions that demand low noise observations from the sensors and the large-field, fast optical telescopes necessary to obtain the science yield. Verifying cryogenic focal plane flatness is challenging because μm level excursions need to be measured within and across many multi-cm sized sensors using no physical contact and while situated within a high-vacuum chamber. We have used an optical metrology Shack-Hartmann scheme to measure the 36x18 cm focal plane developed for the JDEM mission at the Lawrence Berkeley National Laboratory. The focal plane holds a 4x8 array of CCDs and HgCdTe detectors. The flatness measurement scheme uses a telescope-fed micro-lens array that samples the focal plane to determine slope changes of individual sensor zones.
Cryogenic focal plane flatness measurement with optical zone slope tracking
Infrared Sensors, Devices, and Applications; and Single Photon Imaging II, 2011
We describe a non-contact optical measurement method used to determine the surface flatness of a cryogenic sensor array developed for the JDEM mission. Large focal planes envisioned for future visible to near infra-red astronomical large area point-source surveys such as JDEM, WFIRST, or EUCLID must operate at cryogenic temperatures while maintaining focal plane flatness within a few 10's of μm over half-meter scales. These constraints are imposed by sensitivity conditions that demand low noise observations from the sensors and the large-field, fast optical telescopes necessary to obtain the science yield. Verifying cryogenic focal plane flatness is challenging because μm level excursions need to be measured within and across many multi-cm sized sensors using no physical contact and while situated within a high-vacuum chamber. We have used an optical metrology Shack-Hartmann scheme to measure the 36x18 cm focal plane developed for the JDEM mission at the Lawrence Berkeley National Laboratory. The focal plane holds a 4x8 array of CCDs and HgCdTe detectors. The flatness measurement scheme uses a telescope-fed micro-lens array that samples the focal plane to determine slope changes of individual sensor zones.
A CCD system for photometry of direct and spectroscopic images
NASA Conference …, 1984
The authors are using a charge-coupled device (CCD) for direct imagery at the focus of a ground-based telescope and for high dispersion spectroscopy of stars. The CCD is an RCA SID 53612 thinned, buried channel array of 512×320 30-micron square pixels that are back-...
Characterization of the geometry of an array of CCD pixel detectors
EXA05 International Conference on Exotic Atoms and Related Topics
The pixel distance as well as the relative orientation of an array of 6 CCD pixel detector chips have been determined with accuracies of about 1 nm and 50 µrad, respectively. This accuracy satisfies the needs of modern crystal spectroscopy experiments in the field of exotic atoms. Two different measurements have been attempted by illuminating masks in front of the detector array by a remote source of radiation. In one case an aluminum mask was irradiated with X-rays and in a second attempt a nanometric quartz wafer was illuminated by a light bulb. Both methods gave consistent results with a smaller error for the optical method. Furthermore, the thermal expansion with temperature of the CCDs could be determined.
Space Telescope Astrometry from CCD images
Celestial Mechanics & Dynamical Astronomy, 1980
The astrometric application of the Wide Field Camera and the Planetary Camera is reviewed. It is shown that the digital image centering algorithms can yield a positional accuracy of 0.1 milli-arcsecond. Deconvolution of CCD's sensitivity, non-flatness of the filters, and crinkling of the CCD surface may limit the positional accuracy to 1 milli-arcsecond.