Compact multichannel Fourier-transform spectrometer with a Savart-plate interferometer

We have proposed a Fourier-transform spectrometer that uses a multichannel detector and a shearing interferometer.1,2 Because this type of spectrometer contains no moving parts, it has many potential applications, including use as a compact sensor for field use and for time-resolved spectroscopy. In this paper, we present another version of multichannel Fourier-transform spectrometer. In this spectrometer, the radiation to be analyzed is split by a Savart-plate (a birefringent-prism combination) into two beams, and the two beams are recombined on the array detector, where they form forming an interference fringe (interferogram). The interferogram is electronically scanned (read out) and is Fourier-transformed in a computer to reconstruct the spectrum. Because these optics form a source-doubling Fourier transform, the extent of sample/source does not reduce the fringe visibility. As a result, a large field of view is attained. The optical system of the developed spectrometer is compact and stable, and it is easily aligned because of the in-line optical arrangement of the interferometer, which uses only one Fourier-transform lens. The optical system is about 200 mm long uses a Rutile Savart-plate (15 × 15 × 15 mm3). Experimental results of near-infrared defuse-reflectance spectra will be shown for several samples.