Significant enhancement of third harmonic generation in graphene layers placed on a random grating supporting plasmonic Anderson localized states

Abstract

We first theoretically investigate the third-harmonic generation (THG) in a metasurface in which trilayer graphene is deposited over a periodic structure of GaP-CaF2 unit cells. The results of simulation confirm that the output intensity of third-harmonic wave enhances by 229 times around the resonance frequency compared to a bare trilayer graphene surrounded by air. This is due to increase of nonlinear response because of the field enhancement in the graphene layer owing to the excitation of graphene plasmons. Second, to obtain more enhancement for THG, we propose and simulate a metasurface in which the trilayer graphene is deposited on a disordered GaP-CaF2 grating. For this random structure, significant THG occurs at multiple resonance frequencies induced by Anderson localization effect. Our simulation results demonstrate that the maximum output intensity of THG wave increases by 125 times compared to the periodic structure and 28,625 times compared to the bare trilayer graphene. The effects of disorder level are investigated on the output intensity of the THG signal. The number of peaks and the maximum value of THG wave increase with the disorder level. Finally, we study dependence of THG output intensity on the Fermi energy level of graphene. The emission peaks of the THG wave are blue-shifted as Fermi energy increases. Our theoretical prediction of significant enhancement of THG in the graphene based disordered structures needs some experimental evidences in the future to be employed in different applications such as imaging of biological tissues.