Saturable Time-Varying Mirror Based on an Epsilon-Near-Zero Material
Romain Tirole, J. B. Pendry, Jakub Dranczewski, Taran Attavar, Benjamin Tilmann, Yao‐Ting Wang, Paloma A. Huidobro, Andrea Alù, John B. Pendry, Stefan A. Maier, Stefano Vezzoli, Riccardo Sapienza
Abstract
We report a switchable time-varying mirror, composed of an indium-tin-oxide--gold bilayer, displaying a tenfold modulation of reflectivity ($\mathrm{\ensuremath{\Delta}}R\ensuremath{\approx}0.6$), which saturates for a driving-pump intensity ${I}_{\mathrm{pump}}\ensuremath{\approx}100\phantom{\rule{0.2em}{0ex}}\mathrm{GW}/{\mathrm{cm}}^{2}$. 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 below 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 enables applications for spectral manipulation from time-varying systems with impact for communication networks, optical switching, and computing.