# Refraction enhancement in plasmonics by the coherent control of plasmon resonances

## TL;DR

This paper demonstrates how coherent control of coupled plasmonic nanoantennas can enhance refraction and reduce absorption, enabling advanced optical switching and lossless wave propagation in plasmonic metamaterials.

## Contribution

It introduces a classical analogue of quantum EIR in plasmonics, enabling control over nanoantenna polarizability and absorption through phase-shifted coupling.

## Key findings

- Achieved zero absorption or amplification in plasmonic nanoantennas.
- Demonstrated large susceptibility with low dispersion at zero or negative absorption.
- Proposed applications in all-optical switching and lossless wave propagation.

## Abstract

A plasmonic nanoantenna probed by a plane-polarized optical field in a medium with no gain materials can show zero absorption or even amplification, while exhibiting maximal polarizability. This occurs through coupling to an adjacent nanoantenna in a specially designed metamolecule, which is pumped by an orthogonal optical field with phase shift. The introduced scheme is a classical counterpart of an effect known in quantum optics as enhancement of the index of refraction (EIR). In contrary to electromagnetically induced transparency (EIT), where the medium is rendered highly dispersive at the point of zero susceptibility and minimum absorption, in the EIR the system exhibits large susceptibility and low dispersion at the point of zero or negative absorption. The plasmonic analogue of the EIR allows for coherent control over the polarizability and absorption of plasmonic nanoantennas, offering a novel approach to all optical switching and coherent control of transmission, diffraction and polarization conversion properties of plasmonic nanostructures, as well as propagation properties of surface plasmon polaritons on metasurfaces. It may also open up the way for lossless or amplifying propagation of optical waves in zero-index to high refractive index plasmonic metamaterials

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Source: https://tomesphere.com/paper/1903.11888