digicon
{{Short description|Photoelectric effect-derived light detector}}
A digicon detector is a spatially resolved light detector using the photoelectric effect directly. It uses magnetic and electric fields operating in a vacuum to focus the electrons released from a photocathode by incoming light onto a collection of silicon diodes. It is a photon-counting instrument, so most useful for weak sources.{{Cite web|url=http://www.stsci.edu/instrument-news/handbooks/ghrs/GHRS_35.html|title=The Digicon Detectors|website=www.stsci.edu}} One of digicon's advantages is its very large dynamic range and it results from the short response and decay times of silicon diodes.{{Cite book|title=Detection and Spectrometry of Faint Light|last=Meaburn|first=J.|publisher=Springer Science+Business Media, B.V.|year=2012|isbn=9789027711984|location=Dordrecht|pages=36}}
Development
In 1971, E.A. Beaver and Carl McIlwain successfully demonstrated a way in which silicon diodes can be used in digital tube by placing a silicon diode array that contained 38 elements in the same chamber as a photocathode. The design and manufacture of the Digicon tube is attributed to John Choisser of the Electronic Vision Corporation.{{Cite book|title=Advances in Electronics and Electron Physics|last=Morgan|first=B.L.|last2=Airey|first2=R.W.|last3=McMullan|first3=D.|publisher=Academic Press|year=1976|isbn=0120145545|location=London|pages=761}}
Digicon detectors were used on the original instruments for the Hubble Space Telescope, but are very rarely used in new designs, where CMOS active-pixel detectors can achieve the same performance without the need for large electric fields or complicated vacuum assemblies.{{citation needed|date=February 2016}} For instance, there were two pulse-counting Digicon detectors in the Goddard High Resolution Spectrograph installed on the Hubble Space Telescope from 1990–1997, used to record ultraviolet spectra.{{Cite book|url=https://books.google.com/books?id=67joCAAAQBAJ&pg=PA186|title=Astronomy and Astrophysics Abstracts: Volume 42 Literature 1986|last=Böhme|first=S.|last2=Esser|first2=U.|last3=Hefele|first3=H.|last4=Heinrich|first4=I.|last5=Hofmann|first5=W.|last6=Krahn|first6=D.|last7=Matas|first7=V. R.|last8=Schmadel|first8=L. D.|last9=Zech|first9=G.|date=2013|publisher=Springer Science & Business Media|isbn=978-3-662-12382-9|page=186}} Digicon is also used in digital imaging such as the case of a scanning gage using Digicon imaging tube, which generates a two-dimensional view with high spatial resolution when an object is scanned past the Digicon.{{Cite book|title=Practical Applications of Neutron Radiography and Gaging|last=Berger|first=Harold|publisher=ASTM International|year=1976|isbn=0803105355|location=Philadelphia, PA|pages=72}}