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See Inside December 2007

Glow for the Dark

New kind of night vision for the clearest images yet

In 1868 Swedish physicist Anders Ångström discovered that the sky always has a slight glow to it. The light emanates from molecules excited by sunlight or cosmic rays in the upper atmosphere. At night, the amount of airglow is comparable to the light from the full moon spread over the entire sky. But because most of it lies in the short-wave infrared range, the light remains largely invisible—at least to human eyes. Researchers have now devised a camera that could effectively detect this glow to see in the dark better than ever before.

Conventional digital imagers typically rely on silicon, and they do not detect nightglow. But sensors made with germanium, another common semiconductor, can. The problem is that growing germanium crystals using standard semiconductor techniques often leads to defects that can reduce the sensitivity of any resulting sensors. Making high-yield germanium sensors free of defects is very hard, driving up costs and limiting their widespread use.

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