Photocathode
A photocathode (also known as a photocathode ) is a detector for photons that converts incident photons into free electrons using the external photoelectric effect .
Photo cathode consist of a thin semiconductor - metal layer or having a low work function , which in an evacuated (as a vessel on the inside of a window of transparent is applied carrier substrate). The layer thickness is typically a few 10 nm, so that the layers are semi-transparent.
Older photocells carried the photocathode inside on the back of the glass bulb; the layer thickness could therefore be higher in these. The spectral sensitivity varies depending on the material and is in the range between near ultraviolet and near infrared .
In addition to photocells, photocathodes are also used in image converter tubes , image intensifiers , photomultipliers and image pick-up tubes .
Vidicons photocathodes (image pickup tubes) consist of individual metal islands isolated from one another. The image information is created as a charge image and is read out with an electron beam. Conversely, material surfaces can be examined with regard to their structure and composition by irradiating them as a photocathode in a vacuum with light of certain wavelengths and thus determining the work function ( photoelectron spectroscopy ).
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- ^ Dieter Meschede: Optics, light and laser . Vieweg + Teubner, 2008, ISBN 978-3-8351-0143-2 , p. 392 ( limited preview in Google Book search).