Volume electric dipole origin of second-harmonic generation from metallic membrane with non-centrosymmetry patterns

TL;DR

This paper analytically and numerically investigates second-harmonic generation in thin metallic films with non-centrosymmetric patterns, revealing that the dominant electric dipole source originates from the entire volume of the membrane.

Contribution

It demonstrates that volume electric dipoles significantly contribute to SHG in thin metallic membranes, contrasting with the surface-dominated mechanism.

Findings

Bulk SH polarization density is comparable to surface polarization.

Electric dipole originates from the entire volume, not just the surface.

Retardation effects are negligible due to thin film thickness.

Abstract

In this article, we analytically study second harmonic (SH) generation from thin metallic films with subwavelength, non-centrosymmetry patterns. Because the thickness of the film is much smaller than the SH wavelength, retardation effects are negligible. The far-field SH intensities are thus dominated by an effective electric dipole. These analytical observations are further justified numerically by studying the effect of polarization of the fundamental field on both the SH signal and the electric dipole. It is demonstrated that bulk SH polarization density is comparable with its surface counterpart. The electric dipole, consequently, originates from the entire {volume of the metallic membrane, in contrast to the fact that SH generation from metal surface is generally dominated by a surface dipole.