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Disputation Richarda Niemann

Feb 21, 2024 | 04:00 PM
Thema der Dissertation:
Sum-frequency generation microscopy: infrared sub-diffractional imaging of surface phonon polaritons
Abstract: Various super-resolution imaging techniques have been established to overcome the diffraction limit of light. Most of these techniques are limited to resonance imaging in the visible regime, while approaches for the mid- to far-infrared (IR) regime are rare. However, sub-diffractional resolution in the IR is highly relevant when studying phonon polaritons (PhPs), quasi-particles which enable deeply sub-wavelength light confinement in the IR.
This work introduces a novel approach to IR sub-diffractional imaging of PhPs by wide-field sum-frequency generation (SFG) microscopy. Here, the phonon polariton fields are upconverted with a visible laser, resulting in a non-linear SFG signal. This provides IR resonance information at a spatial resolution of 1.4 µm (~ λIR/9) that is well below the IR-diffraction limit. By using a tunable IR free-electron laser (FEL), polaritons can be excited across the whole mid- to far-IR range.
I will demonstrate that the newly developed SFG microscope can be used to image both localized and propagating PhP modes. Localized PhPs were observed in SiC microresonators, where the high spatial resolution allows for microscopic identification of different mode profiles. The observation of propagating PhP modes on an AlN substrate is shown to be enabled by interferometric imaging. Finally, I will discuss hybridized PhPs in a 2D metasurface consisting of SiC microresonators on a SiC substrate. Here, SFG spectro-microscopy allows for two complementary approaches to measure the polariton dispersion, namely angle-dependent resonance imaging and polariton interferometry. The analysis revealed the effect of strong coupling on the localization of polaritons, as well as the formation of photonic edge states.

Time & Location

Feb 21, 2024 | 04:00 PM

Hörsaal A (1.3.14)
Fachbereich Physik, Arnimallee 14, 14195 Berlin