Time reversal of surface plasmons

TL;DR

This paper explores the use of instantaneous time mirrors to achieve time-reversal focusing of surface plasmons on conducting sheets, analyzing how physical parameters affect refocusing quality and wave propagation.

Contribution

It models the effect of sudden changes in Drude weight on surface plasmons using Maxwell's equations and quantifies the resulting wave refocusing and additional free propagating waves.

Findings

Refocusing quality depends on source distance and electron relaxation time.

Instantaneous time mirrors generate both surface and free propagating waves.

Non-instantaneous mirrors cause blurring effects in wave focusing.

Abstract

We study in this work the so-called "instantaneous time mirrors" in the context of surface plasmons. The latter are associated with high frequency waves at the surface of a conducting sheet. Instantaneous time mirrors were introduced by M. Fink et al, with the idea that singular perturbations in the time variable in a wave-type equation create a time-reversed focusing wave. We consider the time-dependent three-dimensional Maxwell's equations, coupled to Drude's model for the description of the surface current. The time mirror is modeled by a sudden, strong, change in the Drude weight of the electrons on the sheet. Our goal is to characterize the time-reversed wave, in particular to quantify the quality of refocusing. We establish that the latter depends on the distance of the source to the sheet, and on some physical parameters such as the relaxation time of the electrons. We also show that, in addition to the plasmonic wave, the time mirror generates a free propagating wave that offers, contrary to the surface wave, some resolution in the direction orthogonal to the sheet. Blurring effects due to non-instantaneous mirrors are finally investigated.