Diffusion in Translucent Media

Diffusion in Translucent Media

Azriel Z. Genack, 
Department of Physics, Queens College and
Graduate Center of the City University of New York, Flushing, New York 11367

Diffusion is the result of repeated random scattering. It governs a wide range of phenomena from Brownian motion, to spin transport in magnetic materials, electronic conduction, heat flow through window panes, neutron flux in fuel rods, and the dispersion of light in human tissue. It is universally acknowledged that the diffusion model fails in translucent samples thinner than the mean free path in which waves propagate ballistically. We show in optical measurements and numerical simulations that the scaling of transmission and the profiles of average intensity for random illumination and for excitation of transmission eigenchannels have the same form in translucent as in opaque media [1]. Paradoxically, the robustness of the diffusive character of steady-state transport in thin samples explains puzzling observations of suppressed optical and ultrasonic delay times relative to predictions of diffusion theory well into the diffusive regime. The source for the common characteristics of propagation in translucent and diffusive media is the shared statistics of transmission eigenvalues.

Reference

[1] Z. Shi and A. Z. Genack, Nature Comm. 9, 1862 (2018).