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Disputation Christopher Jeffrey Winta

17.12.2020 | 16:15
Der Titel der Dissertation lautet:
Second-Harmonic Phonon Spectroscopy Using an Infrared Free-Electron Laser
Abstract: Nonlinear optical spectroscopy constitutes a powerful tool for the investigation of crystalline solids and their structure. Apart from improved sensitivity compared to linear techniques, it offers additional experimental degrees of freedom which can be used to selectively study different symmetry components of the nonlinear signal. The mid-infrared spectral region is particularly interesting as it contains optical phonon resonances which themselves carry symmetry information.
Making use of an infrared free-electron laser (IR FEL), this work explores the potential of IR second-harmonic generation (SHG) as a symmetry-sensitive phonon spectroscopy. To this end, a comprehensive IR SHG study of the model system α-quartz is performed, presenting the technique as a highly sensitive tool to study optical phonons as well as symmetry changes upon structural phase transitions in noncentrosymmetric polar crystals.
Further, second-harmonic phonon spectroscopy is employed for the study of nanophotonic metamaterials, specifically atomic-scale superlattices composed of polar semiconductors. With layer thicknesses on the order of just a few atomic monolayers, new optic phonon modes arise at the many interfaces which are investigated using IR SHG and cause a unique and strongly anisotropic dielectric response of the the heterostructure.
Finally, perspectives on future second-harmonic phonon spectroscopy experiments are discussed.

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17.12.2020 | 16:15