Efficient epsilon-near-zero metasurface for time-varying applications and time diffraction

Time-varying metasurfaces have recently emerged as a new topic of interest for control of light at the nanoscale and exploration of fundamental physics. We demonstrate time diffraction from a time slit in an unstructured metasurface. In a pump-probe experiment, excitation of the Berreman mode of a thin film of Indium-Tin-Oxide over gold leads to strong, efficient all-optical modulation of the film, and to time diffraction of the probe. In comparison to previous works in unstructured epsilon-near-zero films, we obtain a 6 nm frequency shift and a 23 nm broadening using lower intensities and a significantly lower thickness of 40 nm, which demonstrates the minimal footprint of the structure. The deeply subwavelength nature of the sample makes a time-varying interpretation simple and efficient, paving the way for time-dependent architectures for ultrafast optical experiments.