Linear frequency conversion of light via time-varying metasurface

Abstract

The frequencies of electromagnetic waves are found to be linearly converted as the waves propagate through a temporally varying medium.In addition, effective temporal control of the medium, be it artificial or natural, through which the waves are propagating, lies at the heart of linear optical frequency conversion. In this study, we demonstrated tailorable linear frequency conversion with rapidly time-variant metasurfaces at THz frequencies. The proposed metasurface is designed for the sudden merging of two distinct meta-atoms into a single one upon ultrafast optical excitation. From this spectrally-engineered temporal boundary onward, the resonance frequency component of the merged meta-atom is radiated. In addition, temporal coherence of the two original resonating modes with respect to the abrupt temporal boundary is found to be strongly related to the amount of frequency conversion as well as the phase of the converted wave.