Concept of diffusion is widely used to describe propagation of light through multiple scattering media such as clouds, interstellar gas, colloids, paints, biological tissue, etc. Such media are often called random. This terminology is, however, misleading. Notwithstanding its complexity, the process of wave propagation is entirely deterministic – uniquely defined by the exact positions of scattering centers and the shape of the incident wavefront – making it possible to deduce the precise pattern of wave field throughout the system. Technological advances over the last decades enabled one to synthesize arbitrary wavefields opening new frontier in light control inside strongly scattering media.

Coherent excitation of the multiple-scattering medium enabled by wavefront shaping (WFS) requires altogether new approach to predicting and understanding the ultimate limit for a targeted energy delivery into and through a diffusive system, as well as sensitivity of the remitted field to localized perturbations. Indeed, while diffusion-based descriptions have long served as the gold-standard for interpreting e.g. diffuse optical tomography (DOT) and functional near-infrared spectroscopy (fNIRS) measurements, they break down for sample-specific illuminations produced via WFS. An integration of WFS into DOT promises significant improvements in signal strength and, consequently, penetration depth, yet it has lacked a rigorous theoretical foundation. By combining theoretical modeling and physical insight, I will present the groundwork for integrating wavefront shaping into the next generation of optical imaging and sensing technologies – extending their reach and precision in ways not possible within the traditional diffusion-based approaches.

Speaker bio: Alexey Yamilov is a professor of Physics at Missouri S&T. His research activities are in the areas of theoretical and computational condensed matter physics and optics; he employs a variety of analytical and numerical techniques to study transport of the electromagnetic, electronic and other types of waves in the inhomogeneous media, where a line-of-sight propagation is hindered by scattering. The purpose of the research is to uncover and exploit physical phenomena caused by wave interference to: (i) understand behaviors originating not only from the fundamental laws of physics but also from complexity of the system itself; (ii) develop optimal techniques for coherent control of wave propagation; (iii) design structures/systems with a set of desired properties