Theory of electromagnetic wave frequency upconversion in dynamic media

TL;DR

This paper develops a general theory describing electromagnetic wave frequency upconversion in media with decreasing refractive index, revealing energy partitioning limits and efficiency bounds for such processes.

Contribution

It introduces a unified theoretical framework for wave frequency upconversion in dynamic media with decreasing permittivity or permeability.

Findings

Frequency upconversion involves energy partitioning into low-frequency modes.

Efficiency limits are derived for media with decreasing permittivity.

Efficiency bounds are also established for media with decreasing permeability.

Abstract

Frequency upconversion of an electromagnetic wave can occur in ionized plasma with decreasing electric permittivity and in split-ring resonator-structure metamaterials with decreasing magnetic permeability. We develop a general theory to describe the evolution of the wave frequency, amplitude, and energy density in homogeneous media with a temporally decreasing refractive index. We find that upconversion of the wave frequency is necessarily accompanied by partitioning of the wave energy into low-frequency modes, which sets an upper limit on the energy conversion efficiency. The efficiency limits are obtained for both varying permittivity and varying permeability.