Nonlinear absorption in dielectric metamaterials

TL;DR

This paper investigates how nonlinear absorption affects dielectric metamaterials, revealing that it dampens resonances and lowers the threshold for nonlinear effects, impacting their use in optical applications.

Contribution

It provides a detailed analysis of nonlinear absorption effects in dielectric metamaterials, including the impact on resonances and threshold intensities, which was not previously characterized.

Findings

Nonlinear absorption dampens electric and magnetic Mie resonances.

Magnetic resonance is more affected due to larger free-carrier absorption at longer wavelengths.

Field concentration reduces the nonlinear absorption threshold by about 30 times.

Abstract

We solve the nonlinear Maxwell equations in an InP-based dielectric metamaterial, considering both two-photon absorption and photo-induced free-carrier absorption. We obtain the intensity-dependent reflection, absorption, and effective permittivity and permeability of the metamaterial. Our results show that nonlinear absorption dampens both the electric and magnetic Mie resonance, although the magnetic resonance is more affected because it occurs at longer wavelengths where the free-carrier absorption cross section is larger. Owing to field concentration in the metamaterial at resonance, the threshold intensity for nonlinear absorption is smaller by a factor of about 30 compared to a homogeneous layer of the same thickness. Our results have implications on the use of dielectric metamaterials for nonlinear applications such as frequency conversion and optical limiting.