Dual modulation Faraday rotation spectroscopy of HO2 in a flow reactor

Brian Brumfield, Wenting Sun, Yin Wang, Yiguang Ju, Gerard Wysocki

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22 Scopus citations


The technique of dual modulation Faraday rotation spectroscopy (DM-FRS) has been applied to achieve technicalnoise- limited detection of HO2 at the exit of an atmospheric pressure flow reactor. This was implemented by combining direct current modulation at 51 kHz of an external cavity quantum cascade laser system with 610 Hz modulation of the magnetic field generated by a Helmholtz coil. The DM-FRS measurement had a 1.5 times better signal-to-noise ratio than a conventional FRS measurement acquired under identical flow reactor conditions. High harmonic detection of the FRS signal also eliminated the substantial offset associated with electromagnetic interference pickup from the Helmholtz coils that is observed in the conventional FRS spectrum. A noise equivalent angle of 8.9 × 10-9 rad Hz-1/2 was measured for the DM-FRS measurement, corresponding to a 3s detection limit for HO2 of 0.35 ppmv Hz-1/2.

Original languageEnglish (US)
Pages (from-to)1783-1786
Number of pages4
JournalOptics Letters
Issue number7
StatePublished - Apr 1 2014

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics


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