|Category:||Head-Mounted Equipment [HMD/NVG/Glasses]|
|Object Name:||Cats Eyes NVG Image Intensifier Assembly|
|Year of Manufacture:||circa 1990|
|Location:||Main Object Store|
Cats Eyes NVG
This is an Image Intensifier used in the Cats Eyes NVGs. Image intensifiers convert low levels of light photons into electrons, amplify those electrons, and then convert the electrons back into photons of light. Photons from a low-light source enter an objective lens which focuses an image into a photocathode. The photocathode releases electrons via the photoelectric effect as the incoming photons hit it. The electrons are accelerated through a high-voltage potential into a microchannel plate (MCP). Each high-energy electron that strikes the MCP causes the release of many electrons from the MCP in a process called secondary cascaded emission. The MCP is tilted to encourage more electron collisions, thus increasing the amount of emission of secondary electrons.
The electrons all move in a straight line due to the high-voltage difference across the plates, which preserves collimation, and where one or two electrons entered, thousands may emerge. A separate (lower) charge differential accelerates the secondary electrons from the MCP until they hit a phosphor screen at the other end of the intensifier, which releases a photon for every electron. The image on the phosphor screen is focused by an eyepiece lens. The amplification occurs at the microchannel plate stage via its secondary cascaded emission. The phosphor is usually green because the human eye is more sensitive to green than other colours. These devices are identified by ‘Gen’ numbers standing for Generation and today these are at Gen III
Human visual spectral sensitivity ranges from about 400 nm to 700 nm whereas the more third generation tubes are sensitive from about 600 nm to a little over 900 nm. The "Gen III" tubes are about 4 to 5 times more sensitive to night sky illumination than the "Gen II" tubes but they also cost significantly more. But all military types perform significantly better than commercially available Intensifiers.