Dans ce travail, nous nous intéressons à la spectroscopie optique par réflexion d’une vapeur diluée de césium infiltrée dans des opales artificielles Langmuir-Blodgett. Après une étude microscopique de la structure des opales, nous rapportons des expériences de réflexion, transmission et diffraction (sans atomes) effectuées sur diverses opales, dans le but d’explorer la propagation du champ lumineux dans ces milieux. En effectuant des expériences de réflexion sélective, nous observons que pour une polarisation TM, le signal atomique s’annule à 45° et à l’angle de Brewster, et entre ces deux zéros le signe du signal est inversé. Cet effet était prédit théoriquement mais n’avait jamais été observé. Nous rapportons aussi les expériences de spectroscopie par réflexion d’une vapeur infiltrée dans diverses opales et pour différentes longueurs d’onde. Sur des opales multicouches, nous observons des spectres sub-Doppler en incidence oblique, dont la forme est sensible à l’incidence, la polarisation et la longueur d’onde. Ces spectres ont été interprétés comme une signature d’un confinement tridimensionnel. Les expériences sur une opale multizone montre que sur une opale monocouche, nous observons aussi un signal sub-Doppler où il n’y a pas de confinement tridimensionnel. / In this work, we are interested in reflection optical spectroscopy of diluted cesium vapor infiltrated in Langmuir-Blodgett artificial opals. After a microscopic study of the structure of opals, we report experiments of reflection, transmission and diffraction (without atoms) carried out on various opals, with the aim of exploring the propagation of the light field in these media. By carrying out selective reflection experiments, we observe that for a TM polarization the atomic signal vanishes at 45° and the Brewster angle, and between these two zeros the sign of the signal is reversed. This effect was predicted theoretically but had never been observed. We also report the experiments of reflection spectroscopy of a vapor infiltrated in various opals and for different wavelengths. On multi-layered opals, we observe sub-Doppler spectra in oblique incidence, the shape of wich in sensitive to incidence, polarization and wavelength. These spectra were interpreted as a signature of a three-dimensional confinement. Experiments on a multi-zone opal show that on a monolayer opal, we also observe a sub-Doppler signal where there is no three-dimensional confinement.

<p>The University of Massachusetts S-band frequency-modulated, continuous-wave radar (UMass FMCW) was deployed to monitor the growth of the convective boundary layer over northern Alabama during the Verification of the Origins of Rotation in Tornadoes Experiment-Southeast (VORTEX-SE). The Doppler spectra collected in 2016 from the vertically-pointing UMass FMCW contain “spurs”, or spurious spectral peaks, caused by high-voltage switching power supplies in the traveling wave tube amplifier. In the original data processing scheme for this radar, a median filtering method was used to eliminate most of the spurs, but the largest ones persisted, which significantly degraded the quality of derived radar moments (e.g., reflectivity, Doppler velocity, and spectrum width) and hindered further analysis of these data (e.g., boundary layer height tracking). </p><p><br></p><p>In this study, a novel “in-painting” image processing technique was applied to remove the spurs in the Doppler spectra. We hypothesized the in-painting method would exhibit superior performance to the median filter at removing large spectral peaks, and also improve downstream radar products derived from the spectra. First, a Laplacian filter identified and masked spikes in the spectra that were characteristic of the spurs in shape and amplitude. The in-painting method then filled in masked areas based on surrounding data. Via a histogram analysis, the in-painting method was found to be more effective than the median filter at removing the large spurs from the Doppler spectra. The radar moments were then recomputed using a coherent power (CP) technique, resulting in cleaner reflectivity, Doppler velocity, and spectrum width data. Improvement was also found downstream when a boundary layer height detection algorithm was applied to the moments generated from the in- painted spectra. Output from the boundary layer height detection algorithm was then used to verify forecast boundary layer height from the Advanced Regional Prediction System (ARPS) model for the 31 March 2016 VORTEX-SE tornadic case study. </p>

<p>Biodynamic imaging (BDI) is a high-content optical imaging technology based on Fourier-domain digital holography and Doppler spectroscopy of intracellular dynamics. There are three main functions of the BDI technique, which are optical coherence imaging (OCI), motility contrast imaging (MCI) and tissue dynamics spectroscopy (TDS). OCI is related to <em>en face</em> optical coherence tomography (OCT) using partially coherent speckle generated by broad-area illumination with coherence detection through digital holography. MCI provides noninvasive functional imaging by treating intracellular motility as an endogenous dynamic imaging contrast agent. TDS produces broad-band Doppler fluctuation power spectra that contain the ensemble of all intracellular motions by collecting and extracting depth-resolved quasi-elastic dynamic light scattering from inside multicellular living tissue. This thesis presents the development and applications of BDI systems. Doppler spectral clustering analysis is demonstrated when comparing fresh canine lymphoma biopsies and their corresponding flash-Frozen samples. Doppler spectral phenotyping analysis is used to identify a non-predictive phenotype of TDS that shows a systemic red-shift of frequencies. Doppler spectral shift analysis is used to monitor bacterial infection of living tissue. </p>

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