Dresden 2020 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 16: Plasmonics and Nanooptics I: Local Probes and Raman (joint session O/CPP)

CPP 16.5: Vortrag

Montag, 16. März 2020, 11:30–11:45, WIL A317

Polarization-sensitive near-field optical nanoscopy for investigating optical phonon anisotropies at mid-infrared to THz wavelengths — •Lukas Wehmeier¹, Tobias Nörenberg¹, Thales V. A. G. de Oliveira^1,2, J. Michael Klopf², Susanne C. Kehr¹, and Lukas M. Eng^1,3 — ¹Technische Universität Dresden, Germany — ²Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Germany — ³ct.qmat, Dresden-Würzburg Cluster of Excellence - EXC 2147, Technische Universität Dresden, Germany

Polarization-sensitive techniques, such as ellipsometry, are of essential value when investigating optically anisotropic (low-dimensional) materials. Yet, polarization is often neglected in scattering scanning near-field optical microscopy (s-SNOM) and spectroscopy. In a first attempt towards quantitative nano-ellipsometry, we demonstrate here the phonon-enhanced resonant near-field excitation when using both p- and s-polarized incident photons. Notably, we find their near-field responses to be on the same order of magnitude [1]. We apply this s-SNOM mimic for inspecting a broad set of crystalline perovskite materials, i.e. BiFeO₃, PbZrTiO₃, SrTiO₃, and LiNbO₃. Their phonon resonances are easily excited by our setup, making use here of the broad tunability range of the free-electron laser FELBE at Dresden-Rossendorf, Germany [1,2]. Hence, we are able to resonantly excite specific phonons, i.e. a single type of vibronic bonding within the crystal in our s-SNOM setup [2].

[1] L. Wehmeier et al., Phys. Rev. B 100, 035444 (2019).

[2] L. Wehmeier et al., Appl. Phys. Lett., submitted (2019).