Climate change and its consequences are one of the most important issues humanity will have to face in the coming decades. Reliable modeling of climate change can only come from an accurate knowledge of the composition of the atmosphere. Over the last 20 years, an unprecedented number of satellite, balloon and ground-based measurement programs have been developed to sound the atmosphere using optical spectroscopy.
However, the current missions face two main issues: the lack of sensitive portable instruments for in-situ spectral acquisitions and the imperfect knowledge we have regarding the spectroscopic signature of molecules present in the atmosphere.
The main goals of my research program are: (1) to develop portable spectroscopic tools for in-situ detection of atmospheric trace gases, and (2) to measure the absorption parameters of gases of atmospheric importance for use in the analysis of atmospheric spectra and the retrieval of trace gas concentrations.
Spectroscopic characterization of trace gases
Measurements of the
concentration of atmospheric constituents rely greatly on
spectroscopic remote sounding acquisitions from satellite,
balloon-borne, or ground-based platforms.
The processing of the raw experimental data is limited by
our knowledge of the line positions, intensities, and
optical constants of each individual molecule. Incomplete
information on some important greenhouse gases currently
jeopardizes the remote sounding retrieval. Furthermore, many
gases still remain undetected through a total lack of
knowledge of their infrared spectra. Intensive studies of
the spectroscopic signatures of those trace gases are
essential for researchers to take full advantage of
atmospheric measurement data.
This ongoing project
is to make high-accuracy measurements of greenhouse gases
for atmospheric retrieval by mid-infrared tunable quantum
cascade laser spectroscopy. The source is a broadband
mid-infrared laser with a spectral range 7.69-11.83 mm. This
region covers the atmospheric spectral windows were
greenhouse gases are the most potent. There are multiple
molecules that require more accurate measurements. Priority
is given to those currently detectable by remote sensing
from satellites and aircrafts (e.g., glyoxal, methanol,
ethene, propyne, formaldehyde, acetone, and formic acid), or
those that should soon become detectable (e.g. HFCs).
An interesting
additional project is planned in parallel with the same
experimental setup. Analysis of the atmosphere of exoplanets
is a field in expansion. First results had showed a
surprising variety of atmospheric compositions with dominant
gases such as ammonia, methane and acetylene. New programs
like FINESSE (Fast INfrared Exoplanet Spectroscopic Survey
Explorer) may likely provide a large amount of raw data in
the mid-infrared. Proper analysis of those data will depends
on the availabilities of spectra broadened by exotic
molecules. Acquisitions of experimental reference spectra
will be soon performed in this facility.
Cavity-enhanced absorption and whispering-gallery mode spectroscopy
The analysis of atmospheric raw data from remote measurements depends strongly on the retrieval techniques used to extract the information. This can result in important discrepancies between different instruments and requires extensive validation efforts. In situ measurements of trace gas concentrations from balloon-borne or aircraft missions offer a solution to this problem by providing both precise volume-mixing ratio of trace gases at local geographical points and accurate reference values for remote sounding missions. Nevertheless, in situ measurements have always been limited mostly by the heaviness and cost of the payload missions.
New portable
instruments need to be developed to face this issue and
allow a more extensive use of this technique. Miniature
lasers, detectors, and electronic components are already
commercially available. The current main size limitation is
the length of the cavity. But this difficulty can now be
overcome by recent laser spectroscopy techniques. Two
techniques −cavity-enhanced absorption (CEA) spectroscopy
(also called ICOS for Off-axis Cavity Output Spectroscopy)
and whispering-gallery modes (WGM) spectroscopy− have shown
promising results. This project aims to
apply these techniques to the
mid-infrared spectral region where molecules have their
strongest signatures.
Capabilities
A new state-of-the-art facility, the Laser spectroscopy Laboratory, has been built to undertake my research program. This laboratory was mostly funded by the Canadian Foundation for Innovation (CFI) – Leader Opportunity Funds (now renamed John R. Evans Leaders Fund), the Nova Scotia Research and Innovation Trust (NSRIT) matching funds, and a NSERC Discovery Grant.
The masterpiece of the laboratory is a new tunable mid-infrared laser, the MIRcatTM from Daylight Solutions. This powerful laser has one of the largest broadband currently available in the mid-infrared and covers a spectral area corresponding to an important atmospheric spectral window.
Ongoing collaborative research program
In collaboration with Prof. Kimberly Strong and her research group at the University of Toronto, we have developed a research program to improve the reliability of data parameters and infrared cross-sections of greenhouse gases and ozone-depleting substances.
The two geometrical conformations of CFC-113 (Le Bris et al., 2007)
This program includes:
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Theoretical calculation of the optical parameters of atmospheric molecules
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Data acquisition and analysis of Fourier transform infrared spectra of greenhouse gases and ozone depleting substances.
Previous
Physical Chemistry: Spectroscopic studies of rare-earth crystals presenting optoelectronic applications
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Experimental study of the spectroscopic properties of crystals by absorption, emission and Raman spectroscopy
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Determination of crystal field parameters and energy levels of the rare-earth ions by numerical computation
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Implementation of photon echo and hole burning spectroscopy experimental setups
Atomic Physics: High-resolution laser spectroscopy experiments in optically-thick Caesium vapor
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Characterisation of two new spectroscopic techniques, the retrofluorescence and the optovoltaic techniques, to analyse vapour–metallic surface interactions
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Data analysis and theoretical modeling of atoms behaviour at the vapour–surface interface
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Numerical simulations and parametric fits of atomic spectra
Atmospheric Physics: Detection of atmospheric HNO3 molecules by high resolution IR spectroscopy
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Parametric fits of experimental data
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Numerical simulation of absorption line shape of methane induced by CO2 laser