Understanding light-wave propagation in anisotropic materials

26 Sep 2024

Italian group combines spatiotemporal analysis of light transport to resolve interplay of different scattering coefficients.

Understanding how light travels through various materials is essential for many fields, from medical imaging to manufacturing. However, due to their structure, materials often show directional differences in how they scatter light, known as anisotropy.

This complexity has traditionally made it difficult to accurately measure and model their optical properties. Recently, researchers have developed a new technique that could transform how we study these materials.

In a recent study published in Advanced Photonics Nexus, scientists at the European Laboratory for Nonlinear Spectroscopy (LENS), Florence, Italy, introduced an innovative approach to studying anisotropic materials. They combined time-domain transmittance measurements with advanced Monte Carlo simulations to capture the full complexity of how light behaves in these materials.

Method tested on Teflon tape and paper

The researchers tested their method on two common anisotropic materials: Teflon tape and paper. Teflon tape, used widely in industrial settings, and paper, with its structural anisotropy from aligned cellulose fibers, were chosen for their practical relevance.

Using a transient imaging technique, the researchers were able to measure how the light pattern changes over time when materials are exposed to ultrashort pulses of light. This data, paired with a new, anisotropy-aware simulation method, revealed detailed insights into how light scatters differently along various directions within these materials.

The study uncovered notable differences in light diffusion across different directions in both materials, allowing the researchers to retrieve for the first time their full scattering tensor coefficients. This level of detail had not been achieved before, and the results matched predictions from advanced simulations. The findings highlight the importance of accounting for anisotropy in material studies, as ignoring it can lead to significant errors.

Dr. Lorenzo Pattelli from the Italian National Institute of Metrological Research (Istituto Nazionale di Ricerca Metrologica; INRiM), Turin, the lead researcher on the study, emphasized the long-standing challenge of dealing with transport anisotropy.

“Almost all scattering materials show some form of anisotropy. Yet, many studies have ignored this aspect, assuming materials are isotropic for simplicity,” he said, adding, “Due to this oversimplification, we now know that previously reported scattering coefficients in structurally anisotropic media may be quantitatively inaccurate due to the systematic errors introduced by isotropic modeling.”

The new method offers a more accurate way to characterize materials with complex structures, such as biological tissues. This advancement could lead to improvements in diagnostic techniques that rely on light scattering, benefiting fields like medical imaging and material science. With this approach, researchers can better understand and analyze the optical properties of anisotropic materials, lighting the way for more precise applications in various scientific and industrial domains.

• This article was first published on spie.org.