Saturable time-varying mirror based on an ENZ material

TL;DR

This paper demonstrates a switchable, saturable time-varying mirror based on an ITO-Au stack that significantly enhances reflectivity and extends the frequency content of reflected pulses, enabling advanced spectral manipulation for optical applications.

Contribution

Introduces a novel ITO-Au based time-varying mirror with saturation behavior and unprecedented spectral broadening capabilities beyond pump bandwidth.

Findings

Reflectivity modulated ten-fold with saturation at high pump intensity

Frequency content of reflected pulses extended up to 31 THz

Mirror response time shortened from 110 fs to below 30 fs

Abstract

We report a switchable time-varying mirror, composed of an ITO-Au stack, which can be efficiently modulated in time with over a ten-fold increase in reflectivity, with a change of 0.6. Upon interacting with the time-varying mirror, the frequency content of a reflected pulse is extended to 31 THz. This originates from the shortening of the response time of the mirror beyond saturation, as confirmed by a time-varying model and by further four-wave mixing experiments. A temporal response unbounded by the pump bandwidth opens new avenues for spectral manipulation from time-varying systems with impact for communication networks, optical switching and computing. We report a switchable time-varying mirror, composed of an ITO-Au bilayer, displaying a ten-fold modulation of reflectivity ($\Delta R \approx 0.6$), which saturates for a driving pump intensity $I_{\mathrm{pump}}\approx 100$~GW/cm$^2$. Upon interacting with the saturated time-varying mirror, the frequency content of a reflected pulse is extended up to 31 THz, well beyond the pump spectral content (2.8 THz). We interpret the spectral broadening as a progressive shortening of the mirror rise time from 110 fs to sub 30 fs with increasing pump power, which is confirmed by four-wave mixing experiments and partially captured by a linear time-varying model of the mirror. A temporal response unbounded by the pump bandwidth opens new avenues for spectral manipulation from time-varying systems with impact for communication networks, optical switching and computing.