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20 January 2012 Heterodyne-enhanced Faraday rotation spectrometer
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A novel heterodyne-enhanced Faraday rotation spectroscopic (H-FRS) system for trace gas detection of nitric oxide (NO) is demonstrated. The system is based on a quantum cascade laser emitting at ~5.2 μm and a mercury cadmium telluride photodetector (both thermoelectrically cooled). The heterodyne detection is performed at 30MHz, where the laser relative intensity noise is significantly smaller than at low frequencies. With an implementation of active interferometer stabilization technique, the current system shows total noise level that is only 5.4 times above the fundamental shot-noise limit and the Faraday rotation angle sensitivity of 2.6 × 10-8 rad/√Hz. The NO detection limit of 30.7 ppb-v/√Hz was achieved for the R(8.5)e NO transition using 100 Gauss magnetic field and 0.15 m optical path length.
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Yin Wang, Michal Nikodem, Jake Hoyne, and Gerard Wysocki "Heterodyne-enhanced Faraday rotation spectrometer", Proc. SPIE 8268, Quantum Sensing and Nanophotonic Devices IX, 82682F (20 January 2012);

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