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Proceedings Paper

Acousto-optic Spectrometer For Radio Astronomy
Author(s): Gordon Chin; David Buhl; Jose M. Florez
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Paper Abstract

One of the most significant developments in radio astronomy has been the recent discovery of over 50 different molecules in the interstellar medium. These observations have changed our picture of the distribution of mass in the galaxy, altered our understanding of the process of star formation, and has also opened up a new and lively field of interstellar chemistry. This achievement was made possible not only by the development of sensitive heterodyne receivers (front-end))in the centimeter and millimeter range, but also by the construction of sensitive RF spectrometers (back-end) which enabled the spectral lines of molecules to be detected and identified. Traditionally spectrometers have been constructed as banks of discrete adjacently tuned RF filters or as digital auto-correlators. However, a new technique combining acoustic bending of a collimated coherent light beam by a Bragg cell followed by detection by a sensitive array of photodetectors (thus forming a RF acousto-optic spectrometer (AOS) promises to have distinct advantages over older spectrometer technology. An AOS has wide bandwidth, large number of channels, high resolution, and is compact, light weight, and energy efficient. These factors become very important as heterodyne receivers are developed into the submillimeter, far infrared, and 10 micronspectral ranges and as more observations are performed from remote, airborne, or spaceborne platforms. We give a short description and report of existing AOS backends in Australia and Japan but will concentrate on our recent construction of a proto-type AOS at Goddard Space Flight Center. The GSFC AOS uses a discrete bulk acoustic wave Itek Bragg Cell, 5 mW Helium-Neon laser, and a 1024 element Reticon CCPD array. The analog signals from the photodiode array are digitized, added and stored in a very high-speed custom built multiplexer board which allows us to perform synchronous detection of weak signals. The experiment is controlled and the data is displayed and stored with an LSI-11 microcomputer system with dual floppy disks. We will report the performance of the GSFC AOS obtained from our initial tests. We also will give a description of an integrated SAW Bragg cell which will miniaturize a complete AOS system into a 1x3 inch package.

Paper Details

Date Published: 22 August 1980
PDF: 8 pages
Proc. SPIE 0231, 1980 Intl Optical Computing Conf I, (22 August 1980); doi: 10.1117/12.958830
Show Author Affiliations
Gordon Chin, NASA/Goddard Space Flight Center (United States)
David Buhl, NASA/Goddard Space Flight Center (United States)
Jose M. Florez, NASA/Goddard Space Flight Center (United States)

Published in SPIE Proceedings Vol. 0231:
1980 Intl Optical Computing Conf I
William T. Rhodes, Editor(s)

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