Light diffusion and localization in 3D nonlinear disordered media

TL;DR

This paper investigates how light propagates and localizes in three-dimensional disordered media with nonlinear effects, using advanced numerical simulations to reveal diffusion behaviors and a novel nonlinear laser phenomenon.

Contribution

It introduces a comprehensive 3D numerical framework to study linear and nonlinear light transport in disordered media, demonstrating the modulational instability random laser phenomenon.

Findings

Quantitative agreement with experimental diffusion constants.

Evidence of non-exponential decay in transmitted pulses.

Demonstration of modulational instability leading to localized states.

Abstract

Using a 3D Finite-Difference Time-Domain parallel code, we report on the linear and nonlinear propagation of light pulses in a disordered assembly of scatterers, whose spatial distribution is generated by a Molecular Dynamics code; refractive index dispersion is also taken into account. We calculate the static and dynamical diffusion constant of light, while considering a pulsed excitation. Our results are in quantitative agreement with reported experiments, also furnishing evidence of a non-exponential decay of the transmitted pulse in the linear regime and in the presence of localized modes. By using an high power excitation, we numerically demonstrate the ``modulational instability random laser'': at high peak input powers energy is transferred to localized states from the input pulse, via third-order nonlinearity and optical parametric amplification, and this process is signed by a power-dependent non-exponential time-decay of the transmitted pulse.