Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The discovery of graphene and its unique optical and electronic properties triggered intense developments in a vast number of optoelectronic applications, especially in spectral regions that are not easily accessible with conventional semiconductors. Particularly in the THz regime, where the free-carrier interaction with low energetic photons usually dominates, detectors and modulators based on graphene often feature an improved response time. Nevertheless, the light-matter interaction suffers from the small interaction volume. One way to enhance the efficiency of such devices at elevated frequencies, is patterning graphene into plasmonic structures like disks. In addition to the increased linear absorption, the plasmon resonance also creates a strong, surface-localized field that enhances the nonlinear optical response. While experimental studies so far have focused on hot carrier effects, theoretical studies also suggest an increase of the nonlinearity beyond thermal effects. Here we present polarization dependent pump-probe measurements on graphene disks that enable disentangling the contributions of thermal and plasmonic nonlinearity. An increase of the pump-induced transmission is observed when pump and probe radiation are co-polarized. To further elucidate the interplay of thermal and plasmonic effects, we develop a model that supports the origin of the polarization dependent enhancement of the observed THz nonlinearities.