Fourier transform spectrometers are essential for probing the infrared properties of solids, liquids, and gases, in particular their vibrational absorption bands that provide a fingerprint of their composition. The increasing demand for portable spectrometers enabling broadband infrared measurements requires alternatives to the well-known device configuration, in which the sample is probed by two interfering beams incoming from the same light source but traveling with an optical path difference tuned by a moving optical element. In such a configuration, a detector records the transmitted light as a function of the path difference. This yields an interferogram, which is then Fourier transformed to obtain the transmittance spectrum with an excellent resolution. However, devices with moving optical elements do not provide the robustness and cost-effectiveness required by portable spectrometers. In this context, Michael H. Köhler and co-workers propose an alternative Fourier transform spectrometer configuration, in which a fixed concave mirror forms a spatial image of the whole interferogram on a detector array. In contrast with other static configurations, no lens is included in the design. This allows reducing dispersion and temperature-dependence effects, and thus improving the spectrometer performance. A broadband mid-infrared operation from 2800 cm^-1 to 600 cm^-1 with a 12 cm^-1 resolution is demonstrated.

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