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Quantitative characterization of the x-ray imaging capability of rotating modulation collimators with laser light

Gaither III, C. C., III and Schmahl, E. J. and Crannell, C. J. and Dennis, B. R. and Lang, F. L. and Orwig, L. E. and Hartman, C. N. and Hurford, G. J. (1996) Quantitative characterization of the x-ray imaging capability of rotating modulation collimators with laser light. Applied Optics, 35 (34). pp. 6714-6726. ISSN 0003-6935.

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We developed a method for making quantitative characterizations of bi-grid rotating modulation collimators (RMC ’s) that are used in a Fourier transform x-ray imager. With appropriate choices of the collimator spacings, this technique can be implemented with a beam-expanded He -Ne laser to simulate the plane wave produced by a point source at infinity even though the RMC ’s are diffraction limited at the He -Ne wavelength of 632.8 nm. The expanded beam passes through the grid pairs at a small angle with respect to their axis of rotation, and the modulated transmission through the grids as the RMC ’s rotate is detected with a photomultiplier tube. In addition to providing a quantitative characterization of the RMC ’s, the method also produces a measured point response function and provides an end-to-end check of the imaging system. We applied our method to the RMC ’s on the high-energy imaging device (HEIDI) balloon payload in its preflight configuration. We computed the harmonic ratios of the modulation time profile from the laser measurements and compared them with theoretical calculations, including the diffraction effects on irregular grids. Our results indicate the 25-in. (64-cm) x-ray imaging optics on HEIDI are capable of achieving images near the theoretical limit and are not seriously compromised by imperfections in the grids.

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Additional Information:© 1996 Optical Society of America. Received 23 October 1995; revised manuscript received 23 February 1996. C.C. Gaither acknowledges the support of the National Academy of Sciences/National Research Council Research Associateship Program. C.N. Hartman acknowledges the support of the NASA Goddard Space Flight Center (GSFC) Code 730 (especially D. Krueger, D. Dalton, and D. Andrucyk). We are indebted to the GSFC Space Technology Division, Code 710 (Stephen Graham and Jeffrey Travis) for the test electronics. We are also indebted to the GSFC Optics Branch, in particular to John Ostankowski for advice and encouragement with this effort and to Paul Hannon for the schematic design of the advanced laser calibration facility. We thank Julie Ann Watko for assistance with the facility layout and sizing the components. This research was supported in part at the GSFC by NASA Research and Technology Operating Plan 370-04-07 and by the National Science Foundation/Research Experiences for Undergraduates site grant ATM 9400746. At the Catholic University of America, this research was supported in part by NSG 5066. At Caltech this research was supported in part by NAS 5-30792. At the University of Maryland this research was partially supported by NASA grant NAG 5-2001.
Subject Keywords:Fourier transform imaging; imaging systems; laser; applications; optical testing; rotating modulation collimators; x-ray imagers
Issue or Number:34
Record Number:CaltechAUTHORS:GAIao96
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4310
Deposited By: Lindsay Cleary
Deposited On:09 Mar 2020 14:56
Last Modified:02 Oct 2019 23:11

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