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Decades before there were highly
sensitive CMOS-based light sensors and
charge-coupled
devices (CCDs), light detection for image capturing was performed by vacuum
tubes called photomultiplier tubes (PMTs). They amplify light by releasing
electrons in response to a detector surface that answers to photon impingement.
PMTs are still more sensitive and of lower noise level than the silicon devices.
In fact, super-sensitive elements for many atom smashers and subterranean neutrino
detectors still use photomultiplier tubes for that reason. My first encounter with
a PMT was as part of a video
map rendering system used on the airport surveillance radar (ASR) display that
I worked on in the USAF. Air traffic controllers etched an overlay map of the airport
area on a plate of coated glass. It was placed in a box that swept a light beam
in synchronization with the ATC operator's PPI (plan position indicator) display
while the video stream was added to the actual radar display. The method was of
course crude by today's standards, but it actually worked quite well.
World's First Photon Counter
 Counting the photons, or light particles,
arriving from a star is the unusual occupation in which I. M. Levitt (left) and
William Blitzstein were engaged when this photograph was made at the Flower Observatory
in Highland Park, near Philadelphia. A photometer of their own design, which is
the first astronomical device to count such photons, is used by the two scientists
in their experiments. Levitt is shown adjusting the photomultiplier tube attached
to the eyepiece of the telescope while Blitzstein is seen tabulating results obtained
with two RCA Electronic Time Interval Counters, used to count electron impulses
generated by the phototube.
Posted August 22, 2022
(updated from original post
on 8/18/2015)
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