The Production of Film Type Bolometers with Rapid Response

This paper deals with the methods and equipment used in the construction of small high speed bolometers. Particular attention is given to the Type G unit which is rugged, sensitive, and capable of being used satisfactorily with radiation modulated at 30 cycles per second. Special units can be used at considerably higher frequencies. Descriptions are given of methods and equipment for making the cellulose nitrate supporting film and for evaporating thin strips of gold onto this film. Deposition of electrodes and methods of testing for noise and sensitivity during the course of production are described. The use of metal back plates, separated from the bolometer strip by a small distance, is shown to be advantageous. With this construction, and a gas pressure of 20 mm of nitrogen, very satisfactory frequency characteristics are obtained. Gold black is used to increase the absorption of radiation in the vicinity of 10μ. It is pointed out that by controlling the gas pressure either resistive or conductive layers of gold black can be made. In the latter case it is possible to omit the underlying gold strip entirely. Photographs and descriptions of the equipment used for processing bolometers in batches of ten are given, and some of the more interesting points are described in detail. Data are given on frequency characteristics, useful life, and resistance to shock and temperature effects. Finally, brief comment is made on bolometers made of metals other than gold.