# Epsilon-near-zero nonlinearity enhancement in the extreme ultraviolet

## TL;DR

This paper shows how a thin aluminum foil can enhance extreme ultraviolet light interactions, leading to new tools for manipulating XUV radiation.

## Contribution

First experimental demonstration of XUV plasmon-enhanced spectral modification using epsilon-near-zero resonances in aluminum.

## Key findings

- Efficient spectral modification at peak intensities as low as 380 GW/cm2 using aluminum foil.
- Achieved through ultrafast heating and saturation effects in epsilon-near-zero resonances.

## Abstract

Materials with a vanishing dielectric constant provide an ideal platform for achieving plasmon-enhanced light-matter interactions and are widely employed in various cutting-edge nonlinear photonics applications. In this study, we present the first experimental demonstration of extreme ultraviolet (XUV) plasmon-enhanced self-driven spectral modification using a submicrometric foil of aluminium. This is achieved through the excitation of widely tunable Ferrell-Berreman epsilon-near-zero resonances with extremely low absorption. Our angle-dependent measurements of spectral modulation enhancement, supported by theoretical analysis, reveal efficient spectral modification at peak intensities as low as 380 GW/cm2, which we attribute to ultrafast heating and saturation effects. These findings mark a breakthrough in the enhancement of typically weak nonlinearities in the XUV regime through nonlinear plasmonics, potentially paving the way for unprecedented tools for the manipulation and control of XUV radiation.

The first experimental demonstration of extreme ultraviolet (XUV) plasmon-enhanced self-driven spectral modification using a submicrometric foil of aluminium. These findings mark a breakthrough in enhancing XUV nonlinearities.