Broadband wide-angle absorption enhancement due to mode conversion in cold unmagnetized plasmas with periodic density variations

TL;DR

This paper theoretically investigates how periodic density variations in cold unmagnetized plasmas enhance electromagnetic wave absorption over wide angles and frequencies through mode conversion and photonic band effects.

Contribution

It demonstrates that periodic density structures significantly increase mode conversion efficiency and absorption across broad frequency and incident angle ranges.

Findings

Absorption is greatly enhanced within transmission bands.

Wave penetration depth increases, boosting resonance interactions.

Mode conversion efficiency is optimized by the interplay with photonic band structure.

Abstract

We study theoretically the mode conversion and the associated resonant absorption of p-polarized electromagnetic waves into longitudinal plasma oscillations in cold, unmagnetized and stratified plasmas with periodic spatial density variations. We consider sinusoidal density configurations for which the frequency band where mode conversion occurs is well included within a transmission band of the one-dimensional plasma photonic crystal. We calculate the mode conversion coefficient, which measures the fraction of the electromagnetic wave energy absorbed into the plasma, and the spatial distribution of the magnetic field intensity for various values of the wave frequency and the incident angle using the invariant imbedding theory of mode conversion. We find that the absorption is greatly enhanced over a wide range of frequency and incident angle due to the interplay between the mode conversion and the photonic band structure. The enhancement occurs because for frequencies within a transmission band, the wave reflection is strongly suppressed and the waves penetrate more deeply into the inhomogeneous region, thereby increasing the possibility for them to reach many resonance points where the dielectric permittivity vanishes.