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Proceedings Paper

PSF and MTF measurement methods for thick CCD sensor characterization
Author(s): P. Z. Takacs; I. Kotov; J. Frank; P. O'Connor; V. Radeka; D. M. Lawrence
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Paper Abstract

Knowledge of the point spread function (PSF) of the sensors to be used in the Large Synoptic Survey Telescope (LSST) camera is essential for optimal extraction of subtle galaxy shape distortions caused by gravitational weak lensing. We have developed a number of techniques for measuring the PSF of candidate CCD sensors to be used in the LSST camera, each with its own strengths and weaknesses. The two main optical PSF measurement techniques that we use are the direct Virtual Knife Edge (VKE) scan as developed by Karcher, et al.1 and the indirect interference fringe method after Andersen and Sorensen2 that measures the modulation transfer function (MTF) directly. The PSF is derived from the MTF by Fourier transform. Other non-optical PSF measurement techniques that we employ include 55Fe x-ray cluster image size measurements and statistical distribution analysis, and cosmic ray muon track size measurements, but are not addressed here. The VKE technique utilizes a diffraction-limited spot produced by a Point-Projection Microscope (PPM) that is scanned across the sensor with sub-pixel resolution. This technique closely simulates the actual operating condition of the sensor in the telescope with the source spot size having an f/# close to the actual telescope design value. The interference fringe method uses a simple equal-optical-path Michelson-type interferometer with a single-mode fiber source that produces interference fringes with 100% contrast over a wide spatial frequency range sufficient to measure the MTF of the sensor directly. The merits of each measurement technique and results from the various measurement techniques on prototype LSST sensors are presented and compared.

Paper Details

Date Published: 2 July 2010
PDF: 12 pages
Proc. SPIE 7742, High Energy, Optical, and Infrared Detectors for Astronomy IV, 774207 (2 July 2010); doi: 10.1117/12.856738
Show Author Affiliations
P. Z. Takacs, Brookhaven National Lab. (United States)
I. Kotov, Brookhaven National Lab. (United States)
J. Frank, Brookhaven National Lab. (United States)
P. O'Connor, Brookhaven National Lab. (United States)
V. Radeka, Brookhaven National Lab. (United States)
D. M. Lawrence, Brookhaven National Lab. (United States)

Published in SPIE Proceedings Vol. 7742:
High Energy, Optical, and Infrared Detectors for Astronomy IV
Andrew D. Holland; David A. Dorn, Editor(s)

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