Dancing in the Dark- page 5 | How Things Work | Air & Space Magazine
Pointers and illuminators that project infrared light, invisible to the human eye, enable ground commanders and combat controllers in Iraq and Afghanistan to identify targets and designate them for pilots with NVGs. (USAF/Tech. SGT. Scott Reed)

Dancing in the Dark

Night vision goggles can save a pilot's life or, if he hasn't had adequate training, take it.

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Sidebar: The Physics of NVGs

NVGs amplify ambient light that is virtually undetectable to the naked eye and convert it to the visual spectrum on two-dimensional screens in front of each eye. In each tube of the goggles, photons reflected from an object enter through optics that focus the image of the object on the front side of a gallium arsenide photocathode. The photocathode ejects electrons from its back side in proportion to the amount of photons coming in from the front. The process is accelerated by an electrical field that is generated by two AA batteries mounted on the helmet.

The freed electrons ricochet through a micro-channel plate, a thin wafer the size of a quarter with 10 million tiny glass tubules offset eight degrees from the incoming stream and coated on the inside with a material that releases additional electrons with each ricochet, amplifying the input signal thousands of times. The cascading electrons light up a phosphor screen in the eyepiece, painting just an inch or so from the pilot's eyes a representation, in shades of green, of the scene outside.

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