arXiv subjects

Ernesto Pini

Publications and source records attributed to Ernesto Pini.

4 recordsLinked to original sources

arXiv2026

Generalized diffusion theory for radiative transfer in fully anisotropic scattering media

A generalized anisotropic-diffusion framework is developed for transport problem in media described by a tensorial scattering coefficient and a scalar Henyey--Greenstein asymmetry factor. In this regime the classical similarity relation between scattering and transport parameters fails, and each principal diffusion coefficient depends on all components of the microscopic scattering rate. Explicit expressions are derived for the direction-averaged mean free path, the diagonal elements of the diffusion tensor, and boundary condition lengths via rapidly convergent spherical-harmonics expansions, along with open-source implementations. The resulting predictions are validated against anisotropic Monte Carlo simulations, showing excellent agreement across broad ranges of structural anisotropy and phase-function asymmetry factors. The theory provides a compact, general route connecting microscopic anisotropic scattering to macroscopic diffusion coefficients and boundary conditions in bounded geometries.

physics.optics↗

arXiv2024

Experimental determination of effective light transport properties in fully anisotropic media

Structurally anisotropic materials are ubiquitous in several application fields, yet their accurate optical characterization remains challenging due to the lack of general models linking their scattering coefficients to the macroscopic transport observables, and the need to combine multiple measurements to retrieve their direction-dependent values. Here, we present an improved method for the experimental determination of light transport tensor coefficients from the diffusive rates measured along all three directions, based on transient transmittance measurements and a generalized Monte Carlo model. We apply our method to the characterization of light transport properties in two common anisotropic materials - polytetrafluoroethylene (PTFE) tape and paper - highlighting the magnitude of systematic deviations that are typically incurred when neglecting anisotropy.

physics.optics↗

arXiv2024

Diffusion of light in structurally anisotropic media with uniaxial symmetry

Anisotropic light transport is extremely common among scattering materials, yet a comprehensive picture of how macroscopic diffusion is determined by microscopic tensor scattering coefficients is not fully established yet. In this work, we present a theoretical and experimental study of diffusion in structurally anisotropic media with uniaxially symmetric scattering coefficients. Exact analytical relations are derived in the case of index-matched turbid media, unveiling the general relation between microscopic scattering coefficients and the resulting macroscopic diffusion tensor along different directions. Excellent agreement is found against anisotropic Monte Carlo simulations up to high degrees of anisotropy, in contrast with previously proposed approaches. The obtained solutions are used to analyze experimental measurements of anisotropic light transport in polystyrene foam samples under different degrees of uniaxial compression, providing a practical example of their applicability.

physics.optics↗

arXiv2023

Breakdown of self-similarity in light transport

Transport processes underpin a multitude of phenomena, ranging from the propagation of atoms on lattices, to the mobility patterns of microorganisms and earthquakes, to name a few. The dynamics of these processes is very rich and key to understanding the complex nature of the underlying physics, but the way in which we classify them is often too simplistic to fully reflect this complexity. Here, we report on the experimental observation of a breakdown of self-similar propagation for light inside a scattering medium - a transport regime exhibiting different scaling rates for each spatial moment of the associated probability distribution. Notably, we show that this phenomenon arises for light waves even in the simple case of isotropic and homogeneous disorder, and can be controlled by tuning the turbidity of the system. These results support the idea that the traditional dichotomy between normal and anomalous diffusion is reductive and that a richer framework should be constructed based on the concept of self-similarity as this class of transport regimes may be far more common that it is currently believed. In addition, this insight can help understand scenarios where transport is dominated by rare propagation events, as in non-linear and active media, or more generally in other fields of research.

physics.optics↗