Theory of strong localization effects of light in disordered loss or gain media

TL;DR

This paper develops a comprehensive theory describing how strong localization effects of light interact with absorption or gain in disordered media, revealing significant renormalizations and implications for random lasers and oscillatory behaviors.

Contribution

It introduces a selfconsistent Cooperon resummation approach incorporating energy conservation and gain/absorption effects via a generalized Ward identity, advancing understanding of light localization in complex media.

Findings

Finite gain-induced correlation volume smaller than mean free path

Renormalizations depend on whether gain/absorption is in scatterers or background

Implications for random laser feedback and oscillations

Abstract

We present a systematical theory for the interplay of strong localization effects and absorption or gain of classical waves in 3-dimensional, disordered dielectrics. The theory is based on the selfconsistent Cooperon resummation, implementing the effects of energy conservation and its absorptive or emissive corrections by an exact, generalized Ward identity. Substantial renormalizations are found, depending on whether the absorption/gain occurs in the scatterers or in the background medium. We find a finite, gain-induced correlation volume which may be significantly smaller than the scale set by the scattering mean free path, even if there are no truly localized modes. Possible consequences for coherent feedback in random lasers as well as the possibility of oscillatory in time behavior induced by sufficiently strong gain are discussed.