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Cryogen-free heterodyne-enhanced mid-infrared Faraday rotation spectrometer

Author(s): Wang, Yin; Nikodem, Michal; Wysocki, Gerard

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Abstract: A new detection method for Faraday rotation spectra of paramagnetic molecular species is presented. Near shot-noise limited performance in the mid-infrared is demonstrated using a heterodyne enhanced Faraday rotation spectroscopy (H-FRS) system without any cryogenic cooling. Theoretical analysis is performed to estimate the ultimate sensitivity to polarization rotation for both heterodyne and conventional FRS. Sensing of nitric oxide (NO) has been performed with an H-FRS system based on thermoelectrically cooled 5.24 μm quantum cascade laser (QCL) and a mercury-cadmium-telluride photodetector. The QCL relative intensity noise that dominates at low frequencies is largely avoided by performing the heterodyne detection in radio frequency range. H-FRS exhibits a total noise level of only 3.7 times the fundamental shot noise. The achieved sensitivity to polarization rotation of 1.8 × 10-8 rad/Hz1/2 is only 5.6 times higher than the ultimate theoretical sensitivity limit estimated for this system. The path- and bandwidth-normalized NO detection limit of 3.1 ppbv-m/Hz1/2 was achieved using the R(17/2) transition of NO at 1906.73 cm-81.
Publication Date: 14-Jan-2013
Electronic Publication Date: 7-Jan-2013
Citation: Wang, Yin, Nikodem, Michal, Wysocki, Gerard. (2013). Cryogen-free heterodyne-enhanced mid-infrared Faraday rotation spectrometer. Optics Express, 21 (1), 740 - 740. doi:10.1364/OE.21.000740
DOI: doi:10.1364/OE.21.000740
EISSN: 1094-4087
Pages: 740 - 740
Type of Material: Journal Article
Journal/Proceeding Title: Optics Express
Version: Final published version. This is an open access article.

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