Fourier transform infrared spectrometer

Abstract

In an FTIR, a beam splitter, fixed mirrorand movable mirrorare shared by a main interferometerincluding a multiwavelength infrared light sourceand a control interferometerincluding a semiconductor laser. A first detectordetects infrared interference light generated by the main interferometerand transmitted through or reflected by a sample. A second detectordetects monochromatic interference light generated by the control interferometer. A spectrum creatordetermines an optical path difference between an optical path via the fixed mirrorand an optical path via the movable mirror, based on the intensity and uncalibrated oscillation wavelength of the monochromatic interference light detected by the second detector, and creates a spectrum by performing fast Fourier transform on an interferogram which shows a distribution of the intensity of the infrared interference light detected by the first detectorwith respect to the optical path difference. An oscillation wavelength calibratorlocates an absorption peak of carbon dioxide from the peaks in the spectrum created by the spectrum creator, and compares a wavenumber or wavelength of the absorption peak with a true absorption wavenumber or wavelength of carbon dioxide to determine a calibrated oscillation wavelength of the semiconductor laser