Monitoring of hydroxyl free radicals by Off-Axis Integrated Cavity Output Spectroscopy
type: Dataset
description: The hydroxyl free radical (OH) plays a central role in atmospheric chemistry due to its high reactivity with VOCs and other trace species. In this thesis, we demonstrate the feasibility of OH radical detection by means of a compact sensor based on off-axis integrated cavity outpout spectroscopy (OA-ICOS) dedicated to laboratory studies. The developed system requires the coupling of a distributed feedback diode (DFB) emitting in near infrared (∼1435 nm) to a 50 cm long spherical high finesse cavity. The effective interaction path length reaches 1263 m. The off-axis injection of the laser beam allows a detection limit of 2,12 x 10¹¹ OH / cm³. The OA-ICOS is used in combination with wavelength modulation spectroscopy (WMS) by modulating the diode current at 10 kHz. This technique is efficient to remove 1/f noise in the signal. The developed WM-OA-ICOS setup achieves alower detection limit at 5,7 x 10¹⁰OH/cm³. While modulating DFB current, Residual Amplitude Modulation occurs. This background contribution was removed at the optical level by the implementation of a control-loop on the laser intensity before its onjection to the cavity. This stabilisation loop on WM-OA-ICOS achieves a detection limit 5,7 x 10⁹ OH/cm³ for an integration time of 100 s. RAM suppression at the optical level was first used to enhance the detection limit of WM-OA-ICOS setup. It makes our OA-ICOS system one of the most efficient in Noise Equivalent Absorption Sensitivity in the world and provides great opportunities for future development.
landing page: https://theses.hal.science/tel-00874400
identifier: NNT: 2012DUNK0327
keyword: cavite-optique
keyword: couplage-hors-daxe
keyword: coupling-outside-axis
keyword: infoeu-reposemanticsdoctoralthesis
keyword: modulateur-de-longueur-donde
keyword: modulator-of-wavelength
keyword: near-infrared
keyword: optical-cavity
keyword: physcondcm-genphysics-physicscondensed-matter-cond-matother-cond-matother
keyword: proche-infrarouge
keyword: radicals-oh
keyword: radicaux-oh
keyword: spectroscopie-laser
keyword: spectroscopy-laser
keyword: stabilisation-de-puissance
keyword: stabilization-of-power
keyword: theses
issued: 2026-05-09T08:04:55.827760
modified: 2026-05-09T08:04:55.827765
language: fr
contact point: Organization
  fn: CCSD

test_moissonnage_selune
type: Agent

Monitoring of hydroxyl free radicals by Off-Axis Integrated Cavity Output Spectroscopy
type: Distribution
format: HTML
access URL: https://theses.hal.science/tel-00874400
issued: 2026-05-09T08:04:55.829879
modified: 2026-05-09T08:04:55.805716