2010-2013:
IRCSET - Marie Curie INSPIRE fellowship,
Laser Spectroscopy Group, Physics department, University College Cork,
Ireland, and Forschungszentrum Jülich GmbH, Institut für Energie
und Klimaforschung, IEK-8: Troposphäre, Jülich, Germany.
Project:
Broadband cavity-enhanced absorption spectroscopy with long
optical resonators for ultra-sensitive trace gas detection.
2008-2010:
IRCSET Post-doc,
Laser Spectroscopy Group, Physics department, University College Cork,
Ireland. Project:
Broadband cavity-enhanced absorption spectroscopy for the
characterization of local sea-to-air exchange processes.
2007-2008: Marie Curie
Host fellowship for the transfer of knowledge, Laser
Spectroscopy Group, Physics department, University College Cork,
Ireland. Project: Transfer of expertise in atmospheric
monitoring of urban pollutants (TEAM-UP).
2006-2007: Lecturer and
researcher assistant, Physics department, University of Angers. Project:
Light scattering spectroscopy by atomic gases.
2003-2006: - Ph. D. in Physics,
Laboratoire des Propriétés Optiques des Matériaux et
Applications, UMR CNRS 6136, University of Angers, France.
- Lecturer assistant
(moniteur CIES), University of Angers.
Group: Molecular and Atmospheric
Spectroscopy (Angers, France)
Supervisors: Pr. Michel Chrysos,
Dr. Florent Rachet
Title:
Light scattering
spectroscopy by atomic gas mixtures
Context:
The Raman spectrum commonly recorded by a
molecular fluid features the superposition of a standard
contribution dependent on the permanent molecular polarizability
alone, together with a far weaker contribution due to the
interactions between different molecules, mostly two bodies,
usually referred to as the "collision-induced" spectrum. This
last contribution is therefore proportional to the square of the
gas density and is generally highly anisotropic. In the late
60’s, the ‘anisotropic collision-induced’ Raman scattering has
been proved in atomic gases thanks to a conventional right-angle
Raman setup and using gas densities varying from 10 up to 150
amagats. In the late 70’s, Proffitt and Frommhold were the
pioneers measuring the weak and delicate isotropic profiles by
atomic gases and provided a procedure to calibrate the
intensities on an absolute scale. Precise knowledge of these
spectra is indispensable for the determining of macroscopic
electro-optical properties of the medium, such as its refractive
index, its Kerr constant, etc… and also, at a microscopic scale,
for the understanding of the structure of the very short range
inter-atomic interactions (polarizability tensor, energy
potential surface) for which quantum effects mainly participate.
For the last two decades, the
group in Angers has developed a Raman set-up particularly
adapted to the detection of extremely low photon fluxes,
enabling detection of intensities as low as a few photons per
week (i.e. equal to the light flux we would receive on the Earth
from the flame of a candle settled on the Moon). With this
expertise, precise measurements of the very weak, far wings of
Raman spectra of all pure rare gases were possible. My thesis
presents the first experimental and theoretical
collision-induced Raman spectra for two rare gas mixtures, Ne-Ar and Kr-Xe. Such heteronuclar systems are
crucially relevant in order to explain the phenomenon of opacity
observed in the atmospheres of planets.
Group: Laser Spectroscopy Group
(Cork, Ireland)
Supervisor: Dr Andy Ruth
Context:
Application and development
of Cavity enhanced absorption methods for the
spectroscopic detection and characterization of tropospherically
relevant trace species of the atmosphere in the UV, visible and
near infrared
spectral regions. In this context the Laser Spectroscopy Group
in Cork has developed new instrumentation based on
ultra-sensitive BroadBand Cavity-Enhanced Absorption
Spectroscopy (BBCEAS) in order to bridge the gap between
working laboratory experiments and apparati enabling field
studies. Of all new technologies that have been developed in
recent years in atmospheric science, methods that are based on
high finesse optical cavities appear to be the most promising
approach for trace gas detection due to the high spatial and
temporal resolution. The key aspect of the new innovations from
the Cork group is on experimental versatility of the instrument,
its robustness and size.
Open-path BBCEAS instrument set
up at SAPHIR, Jülich, Germany
Wavenumber-resolved interaction-induced Raman scattering
by a gaseous atomic mixture. S. Dixneuf, M.
Chrysos and F. Rachet, J. Raman Spectrosc.36, 139 (2005).
(Link)
Accurate pair-anisotropy models out of a set of input
experimental moments via a novel non-linear inversion method.
M. Chrysos and S. Dixneuf, J.
Raman Spectrosc.36, 158 (2005).
(Link)
Induced anisotropy of (Ar)2: A
state-of-the-art semiempirical model. M. Chrysos and S.
Dixneuf, J. Chem. Phys.122, 184315
(2005).
(Link)
On a singularity-free pair-polarizability anisotropy
model for atomic gases. M. Chrysos, S. Dixneuf and
F. Rachet, J. Chem. Phys.124,
234303 (2006).
(Link)
The time-dependence of molecular iodine emission from
Laminaria digitata. S. Dixneuf, A. A. Ruth, S. Vaughan, R. M.
Varma and J. Orphal,
Atmos. Chem. Phys.9,
823-829(2009).
(Link)
Long optical cavities for open-path monitoring of
atmospheric trace gases and aerosol extinction.
R. M. Varma , D. Venables, A. A. Ruth, U. Heitmann, E. Schlosser
and S. Dixneuf, Applied
Optics48 (4), B159-B171 (2009).
(Link)
Isotropic and
anisotropic collision-induced Raman scattering by monoatomic gas
mixtures: Ne-Ar. S. Dixneuf, M. Chrysos and F. Rachet, Phys.
Rev. A 80, 022703 (2009).
(Link)
Anisotropic
collision-induced Raman scattering by the Kr : Xe gas mixture.
S. Dixneuf, M. Chrysos and F. Rachet, J. Chem. Phys. 131,
074304
(2009). (Link)
Anisotropic
collision-induced Raman scattering by Ne-Ne: Evidence for a
nonsmooth spectral wing. M. Chrysos, S. Dixneuf and F. Rachet,
Phys. Rev. A 80, 054701 (2009).
(Link)
Molecular
iodine emission rates and photosynthetic performance of
different thallus parts of Laminaria digitata (Phaeophyceae)
during emersion. U. Nitschke, A. A. Ruth, S. Dixneuf* and D. B.
Stengel, Planta 233, 737-748 (2011). (Link)
The near
infrared cavity-enhanced absorption spectrum of methyl cyanide.
D. M. O'Leary, A. A. Ruth, S. Dixneuf, J. Orphal and R. Varma,
J. Quant. Spectrosc. Radiat. Transf., doi:
10.1016/j.jqsrt.2012.02.022 (2012).
17th International Conference on Spectral Line
Shapes (ICSLS), June 21-25 2004, Université Pierre et Marie
Curie, Paris, France.
Invited talk:
Recent advances in the far wings of collision-induced scattering
profiles by atomic gases.
Deuxième Colloque Cinétique des Plasmas :
Recherches et Applications (CIPRA2), 6-8 April 2005, Rouen,
France. Spectres de diffusion de la lumière induits par le
mélange atomique Ne-Ar.
EGU General Assembly, April 20-24 2009,
Vienna, Austria. Invited talk:
Incoherent Broadband Cavity-Enhanced Absorption Spectroscopy
for the time-dependent study of iodine
emission from Laminaria Digitata.
Symposium on Cavity Enhanced Absorption
Spectroscopy at the
International Symposium on Molecular
Spectroscopy, 64th
Meeting, Ohio State University,
Columbus, USA, 22-26 June
2009. Time-dependent emission of molecular iodine
from brown seaweed: an application of
incoherent broadband cavity-enhanced absorption spectroscopy.
Liège colloquium Traces
and Tracers, May 2-6 2011, Liège, Belgium. Molecular iodine
emission rates of different thallus parts of Laminaria
digitata determined using incoherent broadband
cavity-enhanced absorption spectroscopy.
Goldschmidt 2011, session
Significance of Iodine in Biogeochemistry and the
Environmental Sciences: Special Session Commemorating the
Bicentennial of the Discovery of Iodine, August 15-19 2011,
Prague, Czech Republic. Molecular iodine emission rates from
Laminaria digitata as a function of algal part,
irradiance and temperature.
European Conference on Nonlinear Optical
Spectroscopy (ECONOS 2004), April 4-6 2004, Erlangen, Germany.
Frequency-resolved interaction-induced light
scattering by a gaseous atomic mixture.
Optimisation of a pair-anisotropy out of a set of
experimental moments via a nonlinear inversion method.
European
Conference On Nonlinear Optical
Spectroscopy (ECONOS 2005), April 11-12 2005, Oxford, England.
Collision-induced light scattering bandshapes by the
Kr-Xe gaseous mixture.
Nonlinear inversion and the trace spectrum of (Ar)2.
Gordon Research Conference on Oscillations
and Dynamic Instabilities in Chemical Systems, July 13-18 2008,
Colby College, Waterville, Maine, USA.
In situ detection of molecular
iodine emission bursts from Laminaria digitata.
Cavity-enhanced
spectroscopy user meeting, June 26-29 2011,
Kingston, Canada.
The
near-IR absorption spectra of gaseous trace
constituents using Fourier-transform broadband
cavity-enhanced absorption spectroscopy.
Laser
Spectroscopy Group
23 February 2012