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PhD thesis Determination of Complex Refractive Index of suspended particles in controled environment by TeraHertz spectroscopy

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Date Limite Candidature : lundi 8 mars 2021

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General information

Reference : UMR8520-SOPBAR-001
Workplace : VILLENEUVE D ASCQ
Date of publication : Monday, February 15, 2021
Scientific Responsible name : Sophie Eliet Barois
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 September 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Scientific background:
On a global scale, aerosols are one of the major components involved in the calculation of the terrestrial radiative balance and therefore of the future evolution of the climate. Their contribution results from numerous direct or indirect effects, the intensity of which will be linked to their concentration in number and the nature of their sources, resulting in a wide variety of physico-chemical properties: particle size, morphology, chemical composition. At the local level, the health impacts of particulate pollution are now sufficiently documented to confirm the harmful role of particles on the health of populations, their toxicity also depending on the size and chemical composition of the particles. A better knowledge of the local and global impacts of aerosols therefore requires having these data on a global coverage with a high temporal resolution. Observation of the atmosphere by remote sensing makes it possible to obtain this crucial information, particularly from spectrometers on board satellite platforms. The challenge of these observations consists in reversing the optical signals recorded over the entire atmospheric column in order to determine the physicochemical properties of the aerosols. This operation requires knowledge of the optical properties and in particular the complex refractive indices (CRI) of aerosols. However, these ICRs are very poorly known in the TeraHertz spectral range (100 GHz-30 THz). It is therefore essential to carry out laboratory experiments in order to measure them. The STEPSON project foresees the development of a spectrometer allowing the characterization of aerosols between 0.2 and 5 THz. This transportable spectrometer can be coupled with other spectrometers (IR and visible) thus making it possible to obtain CRIs over a very wide spectral range never covered until now.

Missions and activities of the doctoral student
The student will have for mission to develop an experimental bench in order to record TeraHertz spectra of resuspended particles whose particle size and concentration will also be recorded.
He / She will have to optimize an existing numerical procedure in order to deduce from it the complex refractive indices of particles. These particles will initially be so-called “model” particles, spherical, calibrated in size and known composition. The student will then have a bank of real samples (desert dust, volcanic ash) on which he / she can carry out his experiments.
Once all these steps have been validated at the IEMN, the instrumentation will be coupled with other spectrometers (UV-Vis and IRTF) so as to acquire datasets from UV to TeraHertz under the same operating conditions.

Work Context

Professional and geographic context
The PhD student will join the Photonics-TeraHertz team of the Institute of Electronics, Microelectronics and Nanotechnologies (IEMN). The student will exercise his / her mission mainly at the central laboratory of the IEMN, located on the Campus Cité Scientifique in Villeneuve d'Ascq, accessible by metro (stop 4 Cantons). He / She will benefit from the instrumental and technical environment of the IEMN platforms. The student will be supervised by Professor Denis Petitprez from the Laboratory of Physico-Chemical Combustion and Atmosphere Processes (PC2A) and by Dr Sophie Eliet, Research Engineer at IEMN. The student will interact with the staff of PC2A and the Atmospheric Optics Laboratory (LOA) (located on the same university campus as the IEMN central laboratory) and will be able to benefit from the equipment and know-how according to the inherent needs of the subject

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