Causality and instability in wave propagation in random time-varying media

We develop a theoretical model to investigate wave propagation in media with random time-varying properties, where temporal fluctuations lead to complex scattering dynamics. Focusing on the ensemble-averaged field, we derive an exact expression for the average Green’s function in the presence of finite temporal disorder, and extend the analysis to the thermodynamic limit. In contrast to spatial disorder, causality prevents recurrent scattering, allowing us to achieve a non-perturbative solution. We introduce an effective medium description providing a simple analysis of the propagation regimes. Our findings offer new insights into wave dynamics in temporally disordered media, with potential applications in time-varying metamaterials, dynamic sensing, and imaging in turbulent or chaotic environments.

💡 Research Summary

In this paper the authors develop a rigorous theoretical framework for wave propagation in media whose properties fluctuate randomly in time. Starting from the scalar wave equation ∇²ψ − ε(t)c²∂²_tψ = 0, they introduce a time‑dependent “potential” V(t) that captures the random modulation of the refractive index or wave speed. The modulation is modeled as a sequence of N infinitesimally short kicks, V(t)=∑_{j=1}^{N}v_j δ(t−t_j), where the kick times t_j are uniformly distributed over a finite interval