Second-Harmonic Phonon Spectroscopy Using an Infrared Free-Electron Laser

PC Online Talk
Date: Nov 19, 2020
Time: 11:00 AM (Local Time Germany)
Speaker: Christopher Winta
FHI Department PC

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 detected signal. The mid-infrared spectral region is particularly interesting as it contains optical phonon resonances which themselves carry symmetry information.

Making use of the FHI free-electron laser (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.

Second-harmonic phonon spectroscopy is then employed for the study of functional material systems. Specifically, atomic-scale semiconductor superlattices and multiferroic thin films are investigated , showcasing the technique's unique capabilities and limitations. Finally, perspectives on how to further develop FEL-based nonlinear optical approaches are presented.

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