Wire mesh interference filters for the infrared
Visinsky, Walter Louis
Low, Frank J.
Master of Science
D. R. Bates (1951) proposed that a principle cooling mechanism for the upper atmosphere is the emission from an atomic oxygen magnetic dipole transition at 63u. Due to the absorption by water vapor this emission is not seeable at ground level, but at 50,000 feet conditions are such that the existence of the line is proveable assuming the existence of a filtering device to isolate the line emiss ion. The design considerations and construction of an interference filter using wire mesh as the reflecting surfaces to operate at 63u is given. Testing of a completed interference filter that operates in second order at 63u indicates that such a device would give the necessary characteristics - small bandwidth, high transmission - to isolate the line emission from the background radiation. The testing of two reference interference filters that operate in second order at 60 and 66u is also given. With interference filters designed to isolate a particular order there must be a means of rejecting all other transmission bands. For the interference filters described above a system is described that will eliminate all radiation below 45u and above 80u so that the only energy detectable will be the second order transmissions of the three interference filters. Finally the use of the interference filters in an experiment to detect the 63u atomic oxygen transmission is described. The expected intensities of the line emission and the emission of water vapor at 50,000 feet (the background) indicated that the use of the interference filters should have proven the existence of the emission line in the upper atmosphere. The experiment was flown at 50,000 feet but a failure in the chopper motor and the filters losing their tautness prevented obtaining any useful data.