Propagating and evanescent waves in absorbing media

TL;DR

This paper compares the behavior of propagating and evanescent waves in absorbing media and draws analogies with quantum particles, highlighting how imaginary components affect wave decay, phase shift, and absorption efficiency.

Contribution

It introduces a unified framework for understanding wave behavior in absorbing media, linking optical and quantum scattering phenomena with new insights on maximizing absorption.

Findings

Imaginary dielectric constant causes exponential decay and phase shifts.

Imaginary potential leads to additional scattering, affecting absorption.

Bound states significantly enhance wave absorption.

Abstract

We compare the behavior of propagating and evanescent light waves in absorbing media with that of electrons in the presence of inelastic scattering. The imaginary part of the dielectric constant results primarily in an exponential decay of a propagating wave, but a phase shift for an evanescent wave. We then describe how the scattering of quantum particles out of a particular coherent channel can be modeled by introducing an imaginary part to the potential in analogy with the optical case. The imaginary part of the potential causes additional scattering which can dominate and actually prevent absorption of the wave for large enough values of the imaginary part. We also discuss the problem of maximizing the absorption of a wave and point out that the existence of a bound state greatly aids absorption. We illustrate this point by considering the absorption of light at the surface of a metal.