Talk:Image intensifier

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Contents 1 Infared is light! 2 Generation IV 3 response... 4 Removal of incorrect statement 5 IR and II ... the same principle? 6 History of... 7 Suggested addition

[edit] Infared is light!

The opening sentence

Unlike a thermographic camera, an image intensifier does not work in total darkness, when there is no light to amplify.

is incorrect, no? Infared light is still light, and a thermographic camera needs infared to function.

Scott5834 18:56, 7 August 2006 (UTC)

Fixed, made the comment more specific about what sort of light Astaroth5 19:39, 7 August 2006 (UTC)

[edit] Generation IV

I was under the impression that Generation IV was officially defined by the US government and has additional standards of amplification and image quality that must be met, besides being gated and filmless. Could you verify this and update accordingly? Gen IV is an existing technology and should be included.

I'd also add a link to here from SLS or starlight scope.

"As good as generation 2 was though, it was soon to be overshadowed by a new photocathode material." That rings kind of strangely to me. The photocathode material for Generations 0-2 is not specified. And it doesn't sound "encyclopedic" but maybe that's not a bad thing.

I'll try to find explanations of how the microchannel plate works... http://hea-www.harvard.edu/HRC/mcp/mcp.html http://www.sciner.com/MCP/MCP.htm Need to get permission to include them. Also, I believe some generation 3 intensifiers used cascades of MCPs to increase gain.

Resolution is maintained in different ways but the common (and simplest) method employed today is to place the plate very near the phosphor screen, minimizing the size of the intensifier tube and relying on the high-voltage field to accelerate the electrons to high kinetic energy in a short distance.

[edit] response...

Last I read, the US military still uses Gen 3 mainly, and Gen 4 is an unofficial designation by manufacturers which is why I distinguished it as such. To my knowledge no generation has ever had requirements, which is why you can get high-end Gen 2+ high-definition tubes that actually exceed the performance of poor Gen 3s. If this has changed, please correct me, but I wasn't able to find anything new on it.

Gen 1 and 2 use a "mutli-alkali" photocathode. I'm not sure of the individual composition of the alkalis in it. I don't know what Gen 0 used.

I agree microchannel plate should have its own article, as MCPs are also used in X-Ray tubes, and possibly other things. I've not heard of MCP cascades though I suppose it's possible.

--the original author

My mistake, I failed to find a single instance of MCP cascades and that is apparently due to the fact that a single MCP can saturate (run out of freeable electrons) relatively easily in high light levels, long before the photocathode burns out. Bombarding a second MCP with the amplified number of electrons from a first is very likely to saturate it. Besides, amplifying light in that way any more than a Generation III tube already does would amplify the noise just as much and probably not be very useful. Switch to thermal. ;)

[edit] Removal of incorrect statement

I've moved this statement here :

"Medical Image Intensifiers work the same way, except the end which receives the X-radiation after it's passed through the subject is coated with a rare earth (typically caesium iodide) which converts the incoming radiation to photons. The photons are accelerated and focussed via electrostatic deflection to an output lens. In older systems, a mirror was mounted above this lens, but now CCTV's are used. These devices are used in Fluorography."

because I'm certain it contains factual errors, photons CANNOT be accelerated electrostaticaly, they always travel at the speed of light in the material they're going through, and cannot be usefully deflected by electrostatic means either. Either the conversion of X-rays to photons is wrong, or the acceleration and deflection is wrong, not sure which. Astaroth5 20:01, 25 April 2006 (UTC)

[edit] IR and II ... the same principle?

I've wondered about this subject for a while. Do active IR sensors and passive visible-light sensors both count as image intensifiers? They seem to work on such different principles, i.e. altering wavelengths versus increasing amplitude. They are usually grouped together though, not just on Wikipedia.

Sometimes it seems like active IR = Gen 0, while passive light-amplification is Gen 1+. Is there no such thing as modern(ised) active IR? Is this called FLIR or is FLIR always passive?

Does passive IR = Thermographic camera and/or thermal imaging?

"... an image intensifier does not work in the total absense of visible (or near infra-red) light." Is near infra-red visible to the naked eye or not? I think the point of the sentence I quoted is that thermographic cameras work on far IR light emitted from warm objects, while Gen 0 II works on reflected far IR light supplied by a lamp, while Gen 1+ II works on ambient visible light, while even later IIs add capability to make (invisible?) IR light visible. Is that correct? Boris B 06:41, 15 August 2006 (UTC)

[edit] History of...

It'd be nice if someone could find print sources for early developments during WWII, that a history section could be expanded. I've so far only found references in web forums and articles (both on German R&D), such as one with pictures of the Vampir rifleman version (in Finnish) and vehicle mounted IR-searchlights. Trouble with the German imagery is that it can't probably be used due to EU copyright.Scoo 09:59, 16 August 2006 (UTC)

[edit] Suggested addition

User:Axharr added the following text to Night vision's stub for Image intensifier. Seems better served here than in the short summary. - Davandron | Talk 21:40, 19 March 2007 (UTC)

The photocathode detects a light image and converts the light image into a corresponding electron pattern. The MCP amplifies the electron pattern and the phosphor screen transforms the amplified electron pattern back to an enhanced light image. --> The photocathode is a photosensitive plate capable of releasing electrons when it is illuminated by light. The number of electrons released by the photocathode is proportional to the intensity of the light impinging on it. The photocathode operates by the principles of the photoelectric effect. More specifically, when a light photon enters the photocathode material and the energy of the photon exceeds the binding energy of an electron to an atom on the surface of the photocathode, the electron is excited from the valence band to the conduction band of the photocathode. The electron is then emitted from the photocathode unto the micro- channel plate. The MCP is a thin glass plate having an array of channels extending between one side (input) and another side (output) of the glass plate. The MCP is positioned between the photocathode and the phosphor screen, An incoming electron from the photocathode enters the input side of the MCP and strikes a channel wall. When voltage is applied across the MCP, these incoming or primary electrons are amplified, generating secondary electrons. The secondary electrons exit the channel at the output side of the MCP and are accelerated towards the phosphor screen. The secondary electrons exiting the MCP channel are negatively charged and are therefore, attracted to the positively charged phosphor screen, which is coated with phosphor. It should be understood that phosphor is any material that emits light when exposed to electron radiation. The energy of the secondary electrons colliding with the phosphor screen causes the phosphor on the screen to reach an excited state and release photons proportional to the quantity of the secondary electrons. The phosphor on the screen glows when photons are released. An eyepiece lens typically magnifies and collimates the glowing phosphor image.