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ÉTUDE DE SPECTROSCOPIE LINÉAIRE ET NON-LINÉAIRE D'AÉROSOLS ATMOSPHÉRIQUES

Abstract : Aerosols are a key component of urban pollution and an essential component of atmospheric physico-chemistry. However, they are poorly characterised and new detection methods are necessary. In that purpose, the present work consists of three parts.
The first axis is the quantitative measurement of urban aerosols over Lyon by a new method combining optical remote sensing by Lidar and analysis of particles impacted on classical samplers. The composition and size distribution of the sampled aerosols are determined by scanning electronic microscopy and X-Ray microanalysis. The extinction and backscattering coefficients are computed from these data using a novel algorithm, which takes the fractal nature of the smaller particles into account.
These coefficients are then used to calibrate the Lidar signal inversion. We therefore get the comprehensive information from the filters to the agility of Lidar which gives an access to the spatial and temporal dynamics of global aerosol concentration. Simultaneously, an epidemiological study on exposure to aerosols was performed by the City of Lyon.
In the same time, in order to measure the catalytic efficiency of the particles surface, we are developing a simulation chamber designed to study a single particle levitated in a quadrupolar trap. We have developed optical non-destructive analysis methods. We determine the particle radius with Mie scattering pattern, composition with micro-Raman spectroscopy, and optical parameters useful for Lidar in an integrating sphere.
Microscopic spherical droplets behave as microcavities, which drastically enhance optical non-linear processes. In order to test new optical remote sensing techniques, we have studied the non-linear scattering by water droplets with radius up to 30 µm, and especially third harmonic generation pumped by ultrashort pulses. The angular distribution is much simpler than in the case of linear Mie scattering, and it depends very weakly on the droplet size. In the same time, our results suggest that the relative lengths of the laser pulse and the cavity may have an essential role in the generation of stimulated processes. This leads us to discuss a non-linear Lidar that could be selectively sensitive to smaller particles.
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Submitted on : Monday, January 23, 2006 - 4:55:08 PM
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Jérôme Kasparian. ÉTUDE DE SPECTROSCOPIE LINÉAIRE ET NON-LINÉAIRE D'AÉROSOLS ATMOSPHÉRIQUES. Physique [physics]. Université Claude Bernard - Lyon I, 1997. Français. ⟨tel-00011446⟩

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