2022-07-04 17:10:19
How do Night Vision Goggles work?Most night vision devices rely on an image intensifier tube, which uses ambient low-light processes as a sort of jumpstart for a process that creates tens of thousands of photons for each original photon. While these devices may use infrared light, they are by no means reliant on them.
The first component of an image intensifier tube is a photocathode, a very thin layer of conductive metal that, when struck by a photon, releases electrons due to the photoelectric effect.
This layer of metal is generally coated with a thin film of protective material, perhaps aluminum oxide, to prevent large positive ions from poisoning the photocathode. This film lowers the efficiency of the photocathode but increases its lifetime tremendously.
These electrons travel through the tube (which is a vacuum), accelerating under the influence of a strong electric field. This acceleration is important for inducing secondary electron emission in the next component of the image intensifier tube, the micro-channel plate detector.
The micro-channel plate detector, true to its name, is a plate with very small holes in it.
These channels are tiny, about 10 micrometers in diameter. Naturally, a single plate contains thousands of these channels. When an electron enters the plate, it bombards the sides of the channel (unless it entered almost perfectly parallel to the channel). If the electron strikes the side with enough energy, it induces the release of more electrons.
These micro-channels have the added benefit of keeping the electrons in the same general position from when they went in, reducing fuzziness. If the electrons were allowed to fly around willy-nilly, the end result would be akin to white noise on a television set.
For each micro-channel, every electron bounce with sufficient energy releases more electrons as they travel down the tube, resulting in a final wave of electrons three to four orders of magnitude larger than the original. This swarm of electrons makes its way to the final component of the image intensifier tube, the phosphor screen.
The phosphor screen is made of a material which releases photons when struck by electrons.
Photons hit a photocathode, which releases electrons. These electrons are multiplied by a micro-channel plate detector. The multiplied electrons hit a phosphor screen, which releases photons that you can see.
368 views14:10