Time reflection emerges as the dual phenomenon of conventional reflection at a spatial interface, and it is induced by an abrupt and spatially uniform change in time of the optical properties of a material, forming a temporal interface. Strong time reflections require ultrafast processes and large modulation amplitudes—conditions that are challenging to achieve. In this work, we demonstrate a new regime for efficient pulse reversal of a pulse that can be accessed through moderate, adiabatic modulation of a plasmonic waveguide. Considering a zinc oxide waveguide with optically tunable carrier concentrations, we show that a slow modulation of the plasma frequency can support efficient temporal reflections based on the reversal of the group velocity rather than of the phase velocity. While interference phenomena do not time-reverse in this setting, the pulse temporal evolution and dispersion do. Our theory unveils the role of broken spatial symmetries in this process and the associated momentum evolution, with opportunities to realize exotic temporal scattering processes within realistic optical setups.

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• Light propagation, transmission & absorption
• Plasmonics
• Time crystals
• Metamaterials
• Waveguides
• T-symmetry