CEAS by optical feedback and its extension into the mid-infrared with quantum cascade lasers

Recent advances in the development of distributed feedback quantum cascade lasers (DFB-QCL) have extended the number of molecular species that can be detected with very high sensitivity by OF-CEAS (Optical Feedback Cavity Enhanced Absorption Spectroscopy). These lasers allow to work in the mid-infrared (MIR) to probe intense transitions of the fundamental level of gaseous species. This allows to gain 2 to 3 orders of magnitude in sensitivity compared to the overtone transitions traditionally exploited by OF-CEAS instruments in the near infrared.

QCL-OFCEAS Instrument Performance :

The LAME team of LIPhy has demonstrated the good suitability of QCL lasers for the OF-CEAS method. Several instruments have been developed with a typical sensitivity of the order of 10-9/cm^-1 in absorption unit for an acquisition time of 1s. Combined with a small volume of gas analyzed (20 cm³) and a short response time (1s), this very high sensitivity is exploited for various fields of application as illustrated by the recent developments of OF-CEAS spectrometers designed with QCL operating at room temperature:

4.30µm : Measurement of the CO₂ isotope ratio for the ¹³C carbon isotope, ¹⁷O containing and doubly substituted minority isotopes (¹⁶O¹³C¹⁸O). This instrument is developed for the analysis of air bubbles trapped in ice within the Subglacior project. The sensitivity on the isotope ratio measurement is of the order of 0.1 ‰ in a few minutes.
4.46µm : N₂O, 546 and 456 isotope ratio measurement for atmospheric chemistry (first demonstration of QCL coupling in an optical cavity, [Maisons,2010])
5.26µm : NO for breath analysis, atmospheric chemistry and outdoor air quality monitoring. Detection limit: < 100pptv in 10s.
5.65µm : HCHO (formaldehyde) for plasma analysis and indoor air quality monitoring. Detection limit: 60 pptv at 10 Hz, with potentially formic acid at the ppb level [Gorrotxategi-Carbajo, 2013].

Spectre OF-CEAS (points noirs) enregistré en 100 ms avec de l’air ambiant. L’ajustement de la simulation, réalisé en temps réel, est tracé en gris. On distingue trois raies d’absorption de l’eau et un doublet faible de H₂CO centré à 1769.46 cm^-1. Une simulation tirée de la base de données HITRAN est tracée en rouge et bleu (décalé pour plus de clarté). La courbe inférieure montre les résidus de l’ajustement [Gorrotxategi-Carbajo, 2013].

Collaborations :

Alcatel Thales III-V lab, Palaiseau, France ;
Laboratoire de Physique des Plasmas (LPP), Ecole Polytechnique, Palaiseau, France ;
Laboratoire de Glaciologie et Geophysique de l’Environnement (LGGE), Grenoble, France ;
Laboratoire TIMC-IMAG (CHU de Grenoble), équipe PRETA, Grenoble, France.

Actors

Daniele ROMANINI
Irène VENTRILLARD