Berlin 2015 – scientific programme
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O: Fachverband Oberflächenphysik
O 36: Plasmonics and Nanooptics
O 36.10: Poster
Tuesday, March 17, 2015, 18:15–21:00, Poster A
Pump-probe infrared near-field nanospectroscopy on germanium and silicon — •Frederik Kuschewski1, S.C. Kehr1, B. Green2, S. Kovalev2, M. Gensch2, and L.M. Eng1 — 1Institut für Angewandte Photophysik, TU Dresden, 01062 Dresden, Germany — 2Helmholtz-Zentrum Dresden-Rossendorf, 01314 Dresden, Germany
Scattering-type scanning near-field optical microscopy (s-SNOM) is a versatile method to map the optical properties on the nanoscale. In combination with novel pulsed THz radiation sources, ultra-short dynamics can be observed in materials of very high interest (e.g. graphene). However, these experiments use very high repetition rates. Here, we introduce a technique to detect minute pump effects in the near-field signal, capable of processing low pumping repetition rates and, hence, allowing for measurements of biological samples.
In s-SNOM, the optical is exctracted via the method of higher-harmonic demodulation, which is extended to a novel side-band technique that allows for the pure measurement of pump-induced effects. In a pilot experiment, we investigated pure Si, Ge and a SiGe thin-film sample under excitation by a Nd:YAG ps laser while near-field probing was carried out by a cw CO2 laser or by the tunable free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf.
All three samples show a time-variable pump-effect in the near-field when being probed at ∼10 µm wavelength. Moreover, image scans proof the resolution far beyond the diffraction limit. The experiment provides a definite proof of the applicability of our approach for investigating ultra fast phenomena in the near-field.