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Home > Teams > LAsers, Molecules and Environment > Themes > Analysis of gas traces

Analysis of gas traces

Guillaume MÉJEAN

Trace gas analysis is more and more demanded for applications in science, as well as in the civil and industrial world. In our group we develop, playing with high finesse cavities and their properties, instruments of different type to respond to some of these needs. A patent was obtained for the technique named OF-CEAS (Optical-Feedback Cavity-Enhanced Absorption Spectroscopy). Several devices have been built based on DFB diode lasers and deployed in different measurement campaigns, in the field and in laboratories. Active projects concern adapting this technique to Quantum Cascade Lasers (QCLs), that emit in the mid-infrared (from 4 to 20 µm and more). Moreover, in order to attain visible wavelengths, we develop systems based on femtosecond Titanium-Sapphire lasers, where the comb of frequencies generated by such a laser is injected into a high finesse cavity. This technique, demonstrated by our group back in 2002, goes under the name of Mode-Locked Cavity Enhanced Absorption Spectroscopy (ML-CEAS).


SARA : analyzer of gas traces

Environmental monitoring requires the analysis of chemical species present in small concentration. This same need exists in the industrial, medical, agro-alimentary domains and more. Our method based on a diode laser and a light trap (an optical resonator) allows to quantify in real time (1s) the traces of several molecules: e.g. those responsible for the greenhouse effect, some atmospheric pollutants, and also some products of human metabolism which can be found in the exhaled air.

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Flight of SARA in the sky of the North Pole

A new application opens up for the OF-CEAS high-finesse cavity laser spectrometer. This analyser of trace gases developed at LIPhy, tool part in the project ENRICHED coordinated by Valery Catoire and his group at the LPC2E laboratory in Orleans (France). This project aimed at collecting data concerning the evolution of stratosphere in Arctic region from winter to spring time. The objective is to supply data to the GIEC3 database which, up to now, does not take into account the lower atmosphere in the modelling of climatic change.

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Femtosecond laser measures trace of atmospheric radicals on the Antarctica continent

An instrument developed in our laboratory is currently analyzing trace amounts of radicals of relevant to atmospheric chemistry in Antarctica. Its working principle is the technique of Mode-Locked Cavity Enhanced Absorption Spectroscopy, "ML-CEAS", introduced in 2002 by Titus Gherman and Daniele Romanini. The instrument relies on the last 10 years of technical progress in robustness and reliability of commercial femtosecond lasers.

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Breath analysis

Optical-Feedback Cavity-Enhanced Absorption Spectroscopy (OF-CEAS) appears as a very promising laser spectroscopy technique for breath analysis. Fast and non-invasive measurements can be performed at a very high sensitivity with a good selectivity of the specie to be measured. This point is of particular importance as hundred of species are present in exhaled air. Furthermore, OF-CEAS offers additional advantages for medical diagnostic: it does not require a calibration with certified gas mixtures, its response time is faster than a single respiratory cycle, it allows the realization of compact and robust instruments that can be operated by non-specialist users in a medical environment.

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Some applications of the "MLCEAS"

The technique « ML-CEAS », «Mode Locked Cavity Enhanced Absoprtion Spectroscopy», was introduced in 2002 by our research group. Since then, several applications of this technique have been tested in the laboratory, demonstrating theversatility and robustness of this technique. Here we present some of these.

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