Patent ID: 7535004

Claim:
A Fourier transform infrared spectrophotometer comprising: a main interferometer section operable to perform a sample measurement operation, said main interferometer section including a beam splitter, a fixed mirror, a movable mirror, and a phase plate disposed between said beam splitter and either one of said fixed and movable mirrors; a control interferometer section having a quadrature control system for separating two types of polarization components from an interference signal combined through said beam splitter, and detecting said separated polarization components so as to calculate a position of said movable mirror based on a phase relationship between the detection signals and respective wavenumbers of the detection signals; means for hangingly supporting said movable mirror in such a manner as to set an initial position of said movable mirror at a gravitationally balanced position; a center-burst-position detection section operable, based on an input of a plurality of interference signals from said control interferometer section and a plurality of interferograms from said main interferometer section, to subject respective intensities of said interferograms to an addition processing while correcting a positional deviation of said movable mirror in each of said interferograms, so as to obtain a cumulative interferogram, and detecting a center burst position having a maximum intensity value in said cumulative interferogram; a center-burst-position storage section operable to store said detected center burst position; and a measurement-start-position determination section operable, based on said center burst position stored in said center-burst-position storage section, to determine a measurement start position of said movable mirror during said measurement operation.