Dresden 2020 – scientific programme
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O: Fachverband Oberflächenphysik
O 9: Plasmonics and Nanooptics I: Local Probes and Raman (joint session O/CPP)
O 9.5: Talk
Monday, March 16, 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 Oliveira1,2, J. Michael Klopf2, Susanne C. Kehr1, and Lukas M. Eng1,3 — 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).