Static Fourier-transform spectrometers have recently been developed that use two Wollaston prisms placed between two polarizers that form an interferogram in the spatial domain. By inclining the optic axis in the Wollaston prism, it is possible to eliminate the need for a second prism. Gluing the polarizers to the faces of the prism gives a single optical component spectrometer approximately 3 mm thick. The interferogram is localised behind the exit face of the prism where it can be recorded by a standard CCD video camera. This allows the spectrometer to be interfaced via a standard frame grabber to a computer which performs a Fourier transform of the data to give the spectrum of the input light. Fourier transform spectrometers can also be used as laser wavemeters where the precision of the wavemeter is set by the number of fringes within the interferogram. For a static Fourier transform spectrometer, the number of pixels across the CCD array limits this severely. However, the lack of moving parts within the spectrometer itself results in an extremely stable output interferogram. This inherent stability can be used to increase the precision beyond that dictated by the number of fringes within the interferogram. If it is assumed that the input light is monochromatic then a measurement of the fringe period gives the wavelength of the source to an arbitrarily high accuracy.
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