Features of Local Electric Field Excitation in Asymmetric Nanocross Illuminated by Ultrafast Laser Pulse

Abstract

Features of the asymmetric nanocross including extinction spectrum, local electric field intensity, and temporal response of the local electric field under ultrashort laser illumination are investigated in this paper. It is found that, due to the simultaneous excitation of local electric fields in the arms that are perpendicular and parallel to the laser polarization direction of the asymmetric nanocross, extinction spectrum exhibits multiple resonant peaks and the position of the peaks can be tuned by changing the lengths of the arms. Simulation results disclose that there is a strong connection between optical response of the parallel and perpendicular arms. Moreover, temporal response of electric field in arms of the asymmetric nanocross shows that oscillations in the parallel arms start earlier than that of the perpendicular arms, and they are in phase when one of the parallel arms resonantly excited, which further reflects the relationship between the parallel and perpendicular arms. Therefore, we demonstrate that the perpendicular arm excitation is attributed to that of the nonresonant parallel arm in the asymmetric structure which cannot keep the overall electric neutrality of the nanostructure, and thus, perpendicular arms are activated to maintain this balance.