Hot electron dynamics in ultrafast multilayer epsilon-near-zero metamaterials

Realizing remarkable tunability in optical properties without sacrificing speed is critical to obtain all optical ultrafast devices. In this work, we investigate the ultrafast temporal behavior of optically tunable epsilon-near-zero (ENZ) metamaterials, operating in the visible spectral range. To perform this the ultrafast dynamics of the hot electrons is acquired by femtosecond pump-probe spectroscopy and studied based on a two-temperature model (2TM). We show that pumping with femtosecond pulses changes the effective permittivity of the metamaterial by more than 400%. This significant modulation is more pronounced in the ENZ region and we confirm this by the 2TM. The realized ultrafast modulation in effective permittivity, along with the ultrashort relaxation time of 3.3 ps, opens another avenue towards ultrafast photonic applications.