Making liquid crystals twitch under metamaterial-enhanced terahertz illumination: toward strong optical nonlinearity

We provide the first direct experimental evidence for the reorientation of liquid crystals by polarized radiation from a conventional, low power, oscillator-based terahertz time-domain spectrometer. Using a terahertz pump - optical probe setup, we observed that the reorientation occurs locally through the resonant amplification of the terahertz field in a specially designed planar metamaterial, adjacent to the liquid crystal layer, and increases with increasing incident terahertz intensity. Our work thus demonstrates that it is possible to induce strong optical nonlinearity in liquid crystals in the terahertz part of the spectrum, paving the way toward the development of new all-optical active terahertz devices as well as electric field sensors for localized resonant systems.