Near infrared wide-band spectroscopy with 27-MHz resolution

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Abstract
For the first time, the resolution of a spectrometer capable of recording very wide spectral ranges is better than 10(-3) cm(-1). This performance, obtained by multipassing an existing Fourier interferometer, is initially intended to get Doppler-limited spectra around 20 microm. The halfwidth of the actual unapodized apparatus function can now be meaningfully expressed in frequency units and is found to be 27 MHz. With such an apparatus it becomes possible to record, from adequate sources, sub-Doppler spectra within wide spectral ranges in the visible and the near ir where the resolution can be easily of the order of 20 times less than the width of the Doppler profiles. The tilt-compensated multipass system which may be used to increase by 3 the resolution of already built Fourier interferometers is described together with the first results obtained on our instrument.