Density of states effects on emission and scattering of photons in plasmas

TL;DR

This paper investigates how the reduced photon density of states in plasmas influences emission, scattering, and spectral properties, highlighting subtle effects and the role of dissipative losses on these phenomena.

Contribution

It provides a detailed analysis of photon DOS effects in plasmas, including their impact on spectral linewidths, scattering, and Lamb shift, with considerations of dissipation.

Findings

Photon DOS in plasma is lower than in vacuum for frequencies above plasma frequency.

Dissipative losses reduce DOS effects but do not eliminate them.

Low-frequency DOS can grow indefinitely due to dissipation.

Abstract

Plasma supports electromagnetic waves propagation for frequencies higher than plasma frequency but features dielectric permittivity less than 1. This property leads to photon density of states (DOS) lower than in vacuum and should result in subnatural spectral linewidths, sub-Planckian spectrum of thermal radiation, and sub-Rayleigh scattering as well as in lower inelastic photon scattering including Raman scattering. Lamb shift will be altered as well though the decisive contribution from high-energy modes in this case makes the photon DOS effect rather small since plasma DOS converges with the vacuum one in the limit of infinite frequencies. We emphasize the basic character of all these phenomena though absolute values of corrections in many real experiments may appear to be small as compared to other factors. We found that dissipative losses make possible DOS effects smaller though not vanishing and additionally bring about indefinite growth of DOS in the low-frequency limit.