Dresden 2017 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 4: Plasmonics and Nanooptics I: Light-Matter Interactions

O 4.9: Vortrag

Montag, 20. März 2017, 12:30–12:45, TRE Ma

Strongly Enhanced Mid-Infrared Second Harmonic Generation from Weak Optical Phonon Modes — •Alexander Paarmann, Ilya Razdolski, Sandy Gewinner, Wieland Schöllkopf, and Martin Wolf — Fritz-Haber-Institut, Berlin, Germany

Mid-infrared second harmonic generation (SHG) spectroscopy [1] provides a unique access to optical phonon resonances in the nonlinear-optical response of polar dielectrics, representing an alternativ spectroscopic approach to established techniques like infrared or Raman spectroscopy. Specifically, the SHG signal is sensitive not only to resonances in the nonlinear susceptibility, but also to the local electromagnetic fields determined by the linear optics. Here, we demonstrate how this intertwined sensitivity can be exploited for enhancement of the SHG specfically for weak oscillators.

Our experiments employ intense, tunable and narrowband mid-infrared pulses from a free-electron laser to acquire SHG excitation spectra from 4H-SiC with the c-axis of the uniaxial crystal in the surface plane [2]. Depending on the crystal azimuthal angle, we observe sharp enhancement of the SHG yield at the frequency of a weak zone-folded mode that exists in 4H-SiC due to the layer stacking along the c-axis. Perspectives are discussed on how to use this effect to detect periodic lattice distortions in strongly correlated insulators.

[1] Paarmann et al., Appl. Phys. Lett. 107, 081101 (2015), [2] Paarmann et al., Phys. Rev. B 94, 134312 (2016)