UFR de Physique

Propositions de stages en laboratoire -- M2

Les offres sont actualisées en mai. Par exemple, les offres de stages pour l'année universitaire 2015-2016 seront mises en place en mai 2015, les offres de stages pour l'année universitaire 2016-2017 seront mises en place pour en mai 2016, etc.

Monitoring of OH radical using Faraday rotation spectroscopy

  • Option Lumière-Matière, Générique du parcours Lumière-Matière
  • Laboratoire: Laboratoire de Physico-Chimie de l'Atmosphère (LPCA)
  • Responsable du stage: CHEN Weidong (chen@univ-littoral.fr, 03 28 65 82 64)
  • Co-responsable(s): Tong-Nguyen BA
  • Mots clés: Faraday rotation, Infrared spectroscopy, OH radical, gas sensing instrument
  • Fiche complète en PDF : Fiche complète en PDF

The hydroxyl radical (OH) is a major atmospheric oxidant that removes 85% CO, 90% CH4, 30% SO2, 50% NO2, and most volatile organic compounds (VOCs) from the Earth’s atmosphere. Therefore, reliable and real-time assessment of the concentration change of OH in the atmosphere is crucial for understanding present and predicting future the atmospheric oxidation capacity, hence the regional air quality and global climate change trends. Faraday rotation spectroscopy (FRS) is a promising spectroscopic technique capable of providing accurate, self-calibration, interference-free and unbiased in-situ measurements of paramagnetic molecules with ultra-high sensitivity. FRS relies on the measurement of a rotation angle of the polarization plane of incident probing laser light, which is induced by Faraday rotation effects resulting from interaction of laser beam with paramagnetic species (such as OH, HO2, etc) in a magnetic field, to infer the concentration of the molecule in interaction PNAS 106 (2009) 12587. FRS technique offers shot-noise limited high detection sensitivity Sci. Rep. 5 (2015) 9096. We recently demonstrated a prototype of FRS instrument for OH radical detection Opt. Express 19 (2011) 2493. Using an active optical path-length of L=25 cm, we achieved a 1σ (SNR=1) detection limit of 8.2×108 OH radicals/cm3. This work showed the potential of realizing a novel, simple, cost-effective, compact, auto-calibration sensor suitable for OH radical monitoring in smog chamber and in-situ field observation. In order to further improve the detection sensitivity, we propose to implement long path absorption approach in the previously developed FRS instrument : using a multipass absorption cell (with an effective absorption pathlength of some tens of meters) to gain a factor of 10-100 in sensitivity in order to lower the detection limit down to less than 107 OH radicals/cm3.