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Mirror coatings: cold reflections.

Mirror coatings: Cold reflections

The most comprehensive tests to date of how well various mirror coatings reflect radiation over a wide range of wavelengths and temperatures have uncovered some surprising effects. The tests, conducted by Virgil E. Sanders of the Los Alamos (N.M.) National Laboratory and his co-workers, reveal that the ability of silver, gold and copper coatings to reflect ultraviolet light unexpectedly declines when they are chilled to 80 kelvins. In the infrared range, metal coatings show the opposite behavior, becoming better reflectors at lower temperatures.

"The big surprise was that it was the same for all the metal coatings," Sanders says. "It seems to be some general phenomenon that is not well understood. It's not talked about in the literature."

The testing was part of a Strategic Defense Initiative program to evaluate coatings for use as mirrors in high-powered lasers. Such lasers generate so much energy that mirrors and other optical elements absorb significant amounts of light, converting it to heat. The heat often distorts the mirrors and sometimes even melts them. The new tests confirm that at the infrared wavelengths at which nigh-powered lasers would operate, silver consistently reflects light better than the other metal coatings, but a layered hafnia-silica glass coating performs even better than the metals.
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Title Annotation:tests on how well various mirror coatings reflect radiation for use in high-powered lasers
Publication:Science News
Date:Apr 13, 1991
Words:212
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