Berlin 2024 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 24: Plasmonics and Nanooptics III: Light-Matter Interaction and Spectroscopy

O 24.6: Vortrag

Dienstag, 19. März 2024, 11:45–12:00, MA 042

Surface phonon polariton ellipsometry — •Giulia Carini, Richarda Niemann, Niclas Sven Müller, Martin Wolf, and Alexander Paarmann — Fritz Haber Institute, Berlin, Germany

Phonon polaritons are light-matter electromagnetic waves emerging in polar crystals from the hybridization of infrared impinging photons with IR-active phonon resonances. The light-matter coupling appears in the bulk polariton dispersion as an avoided crossing and gives rise to a spectral region - known as reststrahlen band (RB) - where the material optically behaves like a metal, only supporting evanescent surface waves, while light propagation inside the crystal is prohibited. The excitation of surface phonon polaritons (SPhPs) requires special experimental schemes to overcome the momentum mismatch between SPhPs and free-space radiation.

In our contribution, we investigate surface phonon polaritons at the interface between gallium phosphide (GaP) and air in momentum-domain by means of the Otto-type prism coupling geometry, a total internal reflection-based approach. Furthermore, we combine this technique with spectroscopic ellipsometry to enable the acquisition of both amplitude and phase information of the reflected waves along the whole RB of GaP. The adjustability of the prism-sample air gap width enables a systematic study of the ellipsometry parameters' dependence on the optical coupling efficiency. In particular, we show that combined observation of both ellipsometry parameters - amplitude and phase - provides a powerful toolkit for the detection of SPhPs, even in the presence of high optical losses.

Keywords: phonon polaritons; ellipsometry; gallium phosphide; Otto-type prism coupling geometry; light-matter coupling