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Octobre 2017

Me., 25.

Colloque de Physique

Exactly solvable models for light-matter interaction

Prof. Daniel Braak, University of Augsburg

Heure: 17:15 - 18:15h

Lieu: UNU-Perolles, Physics Department, building 8, auditorium 0.51, Chemin du Musee 3, 1700 Fribourg

I shall review developments in the theory of elementary models to describe the interaction of light (bosons) with matter (fermions), which have been motivated by the recent dramatic progress towards experimental realization of the so-called deep strong coupling region with possible applications to quantum computing. Relations with the classical theory of analytic functions and the role of discrete and continuous symmetries are especially emphasized.

Je., 26.

Présentation publique de thèse M.Sc.

Finite size effects in time-domain THz ellipsometry

Vjollca ZENKO,Physics Departement of the University of Fribourg

Heure: 16:15 - 17:15h

Lieu: Uni-Perolles, Physics Department, building 8, auditoire 0.51, Chemin du Musee 3, 1700 Fribourg Switzerland

My Master thesis reports scattering effects observed on small transparent samples of acrylic and LSAT using time-domain terahertz rotating analyzer ellipsometer (TD THz RAE). Studies in diffraction with small samples has been done for conducting materials, using conventional ellipsometry, that is with continuous wave in visible and infrared range. Also, theoretical results for conducting material were found regarding the diffraction effects in the spectrum of the ellipsometric angles psi and delta. I extend the subject to pulsed radiation in the THz range and dielectric materials with low and high index of refraction. The focus of my experimental work, using TD THz RAE, was to scan THz pulse profiles in time-domain and investigating about the origin of some unexpected pulses appearing in my scans. Eventually, I found out that these parasitic pulses were results due to the diffraction with the edge of my sample (diffracted pulses), or pulses which propagate inside the material from a side face to the other (side-face pulses). I supported my hypothesis of the side-face effect with a geometrical model which enabled me to calculated the time delay of a side-face pulse and my theoretical data matched well the experimental ones. For the diffracted pulse with the edge, I simply considered, in the theory of diffraction, the shadow zone which is illuminated by radiation which undergoes diffraction with edge. As conclusion, I ran a simulation which showed the interaction of a pulse with a rectangular sample, and the out coming confirmed my assumptions.

Novembre 2017

Je., 09.

Présentation publique de thèse Ph.D.

Laboratory based XAS measurements, Electron-induced double K-shell ionization of Sc, Cr and Cu and Chemical sensitivity of photoinduced Kbeta1,3 hypersatellite transitions in Cr compounds

Faisal ZEESHAN, Physics Department of the University of Fribourg

Heure: 17:00 - 18:00h

Lieu: UNI-Perolles, Physics Department, building 8, auditorium 0.51, Chemin du Musee 3, 1700 Fribourg, Switzerland

The thesis contains three different projects belonging to the domain of X-ray spectroscopy. The first one concerns the development of a laboratory-based setup for in-house X-ray absorption spectroscopy (XAS) measurements. The setup is based on the von Hamos crystal spectrometer of Fribourg using X-ray tubes as radiation sources. The new setup was characterized by measuring the XAS spectra around the K and L edges of several 3d, 4d and 5d transition metals. The edges energies, spectral shapes and absorption coefficients were determined from the data analysis and compared to existing experimental and theoretical data. In the second project the double K-shell ionization of Sc, Cr and Cu induced by electron impact was investigated. The project was also carried out in-house with the von Hamos crystal spectrometer operated in the direct geometry, using the anodes of Sc, Cr and Cu X-ray tubes as targets. The energies and natural line widths of the hypersatellites were determined. The ratios PKK of the double-to-single K-shell ionization cross sections were deduced from the measured relative intensities of the hypersatellites and the results were compared to the PKK values obtained by other groups with electrons, photons and via the nuclear electron capture process. In the third project, the influence of the chemical environment on the Kbeta1,3 hypersatellite transitions was investigated for the first time. The measurements were performed at SSRL using metallic Cr and three Cr compounds corresponding to different oxidation states. For comparison, the diagram Kbeta1,3 and valence-to-core (VtC) Kbeta2,5 transitions were also measured. Relevant dependencies of the energies, energy shifts, relative spectral intensities and line widths on the oxidation state, metal-ligand bond length or spin state could be demonstrated. The observed trends were compared to the ones of the diagram and VtC transitions.

Di., 22.10.2017 - Sa., 18.11.2017

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