|Category:||Head-Mounted Equipment [HMD/NVG/Glasses]|
|Object Name:||Cats Eyes NVG Image Intensifier Assembly|
|Year of Manufacture:||Unknown|
|Location:||Archive 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.
The Cats Eyes NVG system allows for the combination of both a direct visual and an intensified image to be presented to the pilot's eyes. The two images are combined in a 1:1 relationship and complement each other. The Head-Up Display is seen through a direct visual path, and it is not degraded by unnecessary image intensification as it would be with conventional NVG systems. Additionally, the direct vision path through the optical combiner arrangement makes monitoring of cockpit displays and instruments considerably easier while the ability to scan either side of the combiners enhances peripheral vision and ensures better spatial awareness. The direct vision path also removes problems normally associated with light to dark transitions as the intensified image becomes progressively more noticeable as the direct visual image fades. The FLIR image on a HUD is viewed directly and by a simple IR tracker the Image Intensifiers can be turned off whenever the HUD image comes into the field of view of the Cats Eyes.
The folding of the Cats Eyes optical system results in a circular 30 degrees field-of-view with some clipping of the image in the lower right and lower left. The system is compact and rugged, and the restrictions on head mobility imposed by the depth of conventional NVG systems are avoided. While the system incorporates a single handed quick release mechanism for the helmet interface, it can be configured to include an automatic separation system on ejection and designed growth will enable it to accept the latest image intensifier technology as it becomes available. The benefits of the system have been extensively proven in low-level night attack flying trials, which used a fully integrated NVG-compatible cockpit and Forward Looking Infra-Red (FLIR) generated head-up display imagery, together with a head-down multifunction display.
Cats Eyes NVG were sold to the US Marine Corps for the AV8-B and performed well in combat during the 1990-91Gulf War.