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MO: Fachverband Molekülphysik

MO 7: Poster 1

MO 7.23: Poster

Donnerstag, 23. September 2021, 17:30–19:30, P

Time Resolved THz Dynamics in Liquid Crystals — •Patrick Friebel, Klara Maria Neumann, Ivan Trancart, and Laura Cattaneo — Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany

Beyond the typical solid, liquid, and gaseous states of matter, certain materials exhibit mesophase properties, combining attributes of those categories. Liquid crystals (LCs), as a common example, show both solid-like order and fluid-like flow. So far, dynamics occurring within picosecond timescales in LCs are largely unexplored. They show resonant features in the THz spectral region [1], but a clear understanding of these signatures has yet to be developed. Here, we use few cycle THz pulses, generated via optical rectification in the organic crystal DSTMS, to perform both time-domain spectroscopy and resonant time-resolved birefringence measurements on various members of the nCB family of liquid crystals. The measured absorption spectra for uniformly aligned 5CB and 8CB, presenting nematic and smectic A phase, respectively, clearly indicate activity in the THz region. The THz induced birefringence associated with this activity shows oscillatory behaviour after the exciting pulse and thermalization within a few picoseconds. Our time resolved investigation includes dependences on THz-field strength, pump and probe polarization independently controlled with respect to the LC alignment, and temperature, covering phase transitions. Interpretation and attribution to intra- or inter-molecular origin of the data is supported by gas phase theoretical calculations. [1] Vieweg, N., et al., Optics Express, 2012. 20(27)