Abstract
A model L40 American Time Products standard ambient temperature light chopper has been adapted to operate at liquid helium cooled temperatures. The application was in a 2−13 μ three−channel rocketborne infrared radiometer. The chopper tines were copper plated and indium gasket material was inserted between the adjoining tine mount surfaces. These two mechanical modifications, combined with the development of a high−efficiency, chopper−drive circuit, made the adaptation to operation at liquid helium temperatures complete. Locating the chopper in a focal plane away from the detector−preamplifier assembly made it possible to effectively eliminate chopper related capacitive, magnetic, and microphonic coherent noise.
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