DESIGN AND PERFORMANCE OF A DOUBLE BEAM, DOUBLE PASS INFRARED SPECTROPHOTOMETER

Author Institution: The Perkin-Elmer CorporationLast year at Columbus, M. Golay described studies made by Perkin-Elmer comparing various spectrometric systems. Eight systems for double beam, double pass infrared spectrometers were discussed. Of these, one system was chosen as the most desirable for conversion of the Perkin-Elmer Model 21 to a double pass, double beam spectrophotometer. This system, which operates on an optical null principle, is characterized by beam switching at a frequency 2f, by chopping of an intermediate slit image at 3f and by decoding at f. A double pass spectrophotometer has been constructed according to this principle. The conversion parts consist of a single mechanical sub-assembly and quite minor electronic modifications. As expected, the reduction of scattered light is the main performance advantage