Enhanced nonlinear refractive index in epsilon-near-zero materials

TL;DR

This paper demonstrates that epsilon-near-zero materials, specifically Al-doped ZnO thin films, can significantly enhance the nonlinear refractive index, enabling ultrafast and large light-induced changes in material properties.

Contribution

The study introduces a universal approach to enhance nonlinear refractive index using ENZ materials, with experimental validation on AZO films showing a six-fold increase in $n_2$.

Findings

Six-fold increase in Kerr nonlinear refractive index at ENZ wavelength

Ultrafast light-induced refractive index changes of order unity

Demonstration of a new paradigm for nonlinear optics

Abstract

New propagation regimes for light arise from the ability to tune the dielectric permittivity to extremely low values. Here we demonstrate a universal approach based on the low linear permittivity values attained in the epsilon-near-zero (ENZ) regime for enhancing the nonlinear refractive index, which enables remarkable light-induced changes of the material properties. Experiments performed on Al-doped ZnO (AZO) thin films show a six-fold increase of the Kerr nonlinear refractive index ($n_2$) at the ENZ wavelength, located in the 1300 nm region. This in turn leads to ultrafast light-induced refractive index changes of the order of unity, thus representing a new paradigm for nonlinear optics.