GB1103270A - Improvements in and relating to optical interferometers - Google Patents

Abstract

1,103,270. Photo-electric interferometers. SIR HOWARD GRUBB PARSONS & CO. Ltd. May 25, 1966 [June 10, 1965], No.24608/65. Heading G1A. [Also in Division G2] An interferometric spectrometer is used to produce concurrently three interferograms i.e. one for a sample substance, one for a comparison substance and a reference interferogram relating to the background energy in the interfering beam paths when neither a sample nor a comparison sample is present therein. From the interferograms, transmittance spectra may be obtained for the sample and comparison substances. A Michelson interferometer Fig. 1 (not shown) similar to one described in Patent Specification 1,056, 566 may be used. The sample and comparison substances are mounted in respective compartments of a holder (Fig. 3) with an empty compartment or open aperture providing the background reference and introduced in a predetermined sequence at regular increments or decrements of path difference of the two interfering beam paths of the interferometer, while this path difference is changed either continuously or in discrete steps. The absorption by the sample and comparison substances changes with the change in path length and is detected by a Golay cell, the output of which is recorded on a punched tape, representing the three concurrently recorded interferograms. The tape can be processed by a digital computer, and if the transmittance spectrum of the comparison substance obtained from this compares well with its spectrum obtained by known methods the transmittance (or absorption spectrum) of the sample is correct. Mathematical expressions used by the computer for obtaining this spectrum are given and their derivation obtained. Further comparison or sample substances may be arranged in the holder, to produce four or more concurrent interferograms.