What is Image Intensifier tube and How does it work?

2021-09-13

What is Image Intensifier tube and How does it work?

An image intensifier tube is a device that intensifies (or amplifies) low light level images to levels that can be seen by human eye or detected by digital image sensors.

All modern image intensifier tube are consist of three main components, a photocathode,

a Micro-channel Plate(MCP）and a phosphor screen. The characteristics of each components will contribute to the overall quality of the resulting image.

Image intensifier tubes collect the existing ambient light such as starlight , moonlight, or from artificial sources such as streetlights or infrared illuminators.

The low level of incoming light, which consists of photons, enters the tube through its input window and strikes the photocathode(a very light sensitive layer deposited on the inside of the image intensifier tube input window that converts the photons into electrons and releases them into the vacuum of the tube). Once released by the photocathode, these photo-electrons are accelerated and focused by a high electrical field towards the MCP (MCP is a thin glass disc, less than a half a millimeter thick,which contains millions of small channels)

When an electron coming from the photocathode strikes the wall of one channel, serval secondary electrons are generated by the impact. each of these secondary electrons will in turn be accelerated with the MCP by another high electrical field, once again striking the inner wall of the channel, and generating even more secondary electrons. This process is repeated along the depth of the MCP channels. For each electron that enters the MCP, approximately one thousand electrons are generated and subsequently accelerated from the output of the MCP by a third electrical field towards the phosphor screen.(The phospher screen is a thin phosphorous light emitting layer depositated on the inside of the output window of the intensifier tube  which converts the electrons back into photons.)

When the multiplied flow of electrons out of the MCP strike that layer, tens of thousands of photons will be generated for every single photon that was initially converted by the photocathode.

This entire multistage process creates and intensified image, much brighter than the original image, which ca subsequently be seen by the human eye.