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Proceedings Paper

Faraday rotation spectroscopy of nitrogen dioxide based on a widely tunable external cavity quantum cascade laser
Author(s): Christian A. Zaugg; Rafal Lewicki; Tim Day; Robert F. Curl; Frank K. Tittel
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Paper Abstract

Faraday Rotation Spectroscopy (FRS) is a technique for the sensitive and selective detection of paramagnetic molecules or radicals such as NO, NO2, O2 or OH-. Moreover FRS is suitable for atmospheric measurements due to the insensitivity to non-paramagnetic interfering molecules such as H2O and CO2. Experimental results of an FRS sensor for the NO2detection employing an external-cavity quantum cascade laser (EC-QCL) are reported. The CW EC-QCL exhibits modehop free (MHF) tuning between 1600 cm-1 and 1650 cm-1. This allows targeting the optimum 441←440 Q-branch NO2transition at 1613.25 cm-1. A rotation of the polarization state of the initially linearly polarized laser light is observed when an AC magnetic field is applied to the NO2 cell, placed between two nearly crossed Rochon polarizers. This rotation of the polarization state is proportional to the NO2 concentration and can be determined by a photodetector located after the second polarizer. For long-term continuous measurements a second branch consisting of a detector and reference cell filled with 0.2 % NO2 in N2 is used to lock the laser to the selected NO2 transition. A minimum detection sensitivity (1σ) of 1 parts per billion (ppbv) was obtained for a 1 sec lock-in time constant (TC).

Paper Details

Date Published: 24 January 2011
PDF: 7 pages
Proc. SPIE 7945, Quantum Sensing and Nanophotonic Devices VIII, 79450O (24 January 2011); doi: 10.1117/12.874819
Show Author Affiliations
Christian A. Zaugg, ETH Zurich (Switzerland)
Rafal Lewicki, Rice Univ. (United States)
Tim Day, Daylight Solutions Inc. (United States)
Robert F. Curl, Rice Univ. (United States)
Frank K. Tittel, Rice Univ. (United States)

Published in SPIE Proceedings Vol. 7945:
Quantum Sensing and Nanophotonic Devices VIII
Manijeh Razeghi; Rengarajan Sudharsanan; Gail J. Brown, Editor(s)

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