Light scattering from a magnetically tunable dense random medium with weak dissipation : ferrofluid

TL;DR

This paper investigates how a magnetically tunable ferrofluid affects light scattering, transmission, and reflection, revealing the interplay of disorder, partial order, and weak dissipation in controlling light transport and localization.

Contribution

It introduces a semi-phenomenological model combining disorder and Bragg scattering in ferrofluids, supported by experimental observations, to explore light behavior near Anderson localization conditions.

Findings

Transmission and reflection decrease when tuned to Bragg condition

Partial spatial order enhances scattering and localization

Experimental results qualitatively agree with theoretical predictions

Abstract

We present a semi-phenomenological treatment of light transmission through and its reflection from a ferrofluid, which we regard as a magnetically tunable system of dense random dielectric scatterers with weak dissipation. Partial spatial ordering is introduced by the application of a transverse magnetic field that superimposes a periodic modulation on the dielectric randomess. This introduces Bragg scattering which effectively enhances the scattering due to disorder alone, and thus reduces the elastic mean free path towards Anderson localization. Our theoretical treatment, based on invariant imbedding, gives a simultaneous decrease of transmission and reflection without change of incident linear polarisation as the spatial order is tuned magnetically to the Bragg condition, namely the light wave vector being equal to half the Bragg vector (Q). Our experimental observations are in qualitative agreement with these results. We have also given expressions for the transit (sojourn) time of light and for the light energy stored in the random medium under steady illumination. The ferrofluid thus provides an interesting physical realization of effectively a "Lossy Anderson-Bragg" (LAB) cavity with which to study the effect of the interplay of spatial disorder, partial order and weak dissipation on light transport. Given the current interest in propagation, optical limiting and storage of light in ferrofluids, the present work seems topical.