Elliptically polarized second-harmonic generation by local magnetic field in terahertz chiral metamaterials

Abstract

Elliptically polarized second-harmonic generation (SHG) is achieved in the terahertz region with a chiral metamaterial consisting of a gold gammadion and a doped GaAs cut wire under circularly polarized excitation. Remarkable SHG-circular dichroism (SHG-CD) is attributed to the local magnetic field induced by the magnetic resonance in the chiral gammadion and the current generated in the GaAs wire. The SHG-CD follows the parity conservation when the parity of the chiral metamaterial changes. The maximal modulation depth of the ellipticity and the polarization rotation angle of the SHG reach 91% and 72°, respectively, resulting from the change of the second harmonic field current density with different wire lengths. This work deepens the understanding of the nonlinear optical effect in metamaterials and puts forward the chiral metamaterials as efficient and helicity-tunable nonlinear terahertz sources.