Redepositing electrons on photocathode ?

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SUMMARY

The discussion centers on the sensitivity loss of image intensifier tubes, specifically regarding the photocathode's ability to produce free electrons. Users Starman and Zz clarify that the sensitivity loss is not due to a depletion of electrons but rather due to oxidation and surface degradation of the photocathode material. Zz emphasizes that applying a reversed high voltage for electron redeposition is ineffective and could further damage the photocathode. Recoating the photocathode may be possible, depending on the alkali metal used and substrate characteristics, but it is not guaranteed to restore functionality.

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  • Understanding of image intensifier tube components, including photocathodes and micro channel plates.
  • Knowledge of electron behavior in vacuum tubes and high-voltage applications.
  • Familiarity with alkali metals and their properties in photocathode applications.
  • Basic concepts of thin film coating techniques and their dependency on substrate characteristics.
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  • Research the properties and applications of different alkali metals used in photocathodes.
  • Explore techniques for thin film coating and its impact on photocathode performance.
  • Investigate methods for assessing and mitigating oxidation and surface degradation in photocathodes.
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Optoelectronic engineers, technicians working with image intensifier tubes, and researchers focused on photocathode technology and restoration methods.

starman2006
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Redepositing electrons on photocathode ??

Hello All
I'm new to the forum and have a question i hope one of you can answer.
I have 3 surplus image imtensifier tubes...all of which have lost there sensiitivity to one degree or another. To review; an image intensifier tube conssits of a photo cathode ( a thin layer of alkili metals deposited on a glass window) ... a micro channel plate...and a phosper screen...all located inside a vacuum tube. When a photon of light hits the photocathode it knocks an electron free...the electron is then accelarted by a high voltage to the micro channel plate, where it knocks off more electrons...and then these electrons are accelerated by another high voltage and hit the phospor screen producing light. In the image tubes i have, the photo cathodes have lost sensitivity...that is they have lost some of their ability to produce a free electron when a photon of light strikes. My question is...would there be some way to resupply the alkili metals of the photo cathode with electrons...perhaps by supplying the photochode with a REVERSED high voltage..causing electrons to redeposit into the alkili metals or is that to much to hope for.
Thanks for any help you may be able to give.
Starman
 
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Er.. no. The lost in "sensitivity" is not due to a depletion of electrons in the photocathode - the photocathode is always grounded, even during operations. If not, you will have a charging effect and the photocathode will stop working efficiently after only a few seconds. So the material itself is not depleted with electrons. Thus, back bombardment will not help and in fact, may even destroy it more.

Oxidation, surface degradation, etc.. all cause the cathode to change characteristics over time. Depending on what kind of alkali metal that was used, it may be possible to recoat the surface, but this isn't guaranteed since thin film coating depends on many things, including substrate characteristics.

So no, back bombardment will not work.

Zz.
 

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