Light-Matter Interaction: Laser Challenges Classical
Laws of Diffusion
Abstract
The interaction between electromagnetic radiation and matter is one of the most ubiquitous and influential phenomena in nature, underpinning various fundamental processes across physics, chemistry, and materials science. At its core, this interaction is reciprocal, reflecting a dynamic interplay between light and the medium through which it propagates. On the one hand, the properties of light are largely determined by the parameters of propagation environment. On the other hand, the optical fields actively reshape the microscopic landscape of the materials, modifying electronic states, inducing structural transformations, driving mass transport, etc. This talk presents an overview of recent state-of-the-art advances in both aspects, spanning fundamental insights and emerging applications.
I'll show that although light propagation in random dielectric media is often described using diffusion theory, wave interference leads to fundamentally different transport behavior. In particular, transmission is governed by a set of eigenchannels with highly non-uniform transmission probabilities. The distribution of the transmission coefficients is bimodal, such that the most of the channels are either nearly fully open or strongly closed. Remarkably, these channels suppress transverse spreading and preserve their spatial structures throughout the sample, in striking contrast to the intuition built on classical particle diffusion.
The impact of light on the photo-induced mass transfer in amorphous media will be illustrated using chalcogenide glasses as an example. Under coherent laser radiation, these materials exhibit nanoscale-to-microscale redistribution of matter, leading to spontaneous formation of surface relief structures and compositional gradients. This behavior indicates that optical fields modify microscopic mechanisms governing the mobility of structural units and the forces responsible for their displacement. The results reveal that photo-induced diffusion is a light-driven mass transport rather than a purely thermally activated phenomenon.
Finally, I'll demonstrate how light serves as a powerful non-invasive tool for probing and controlling material systems, enabling real-time access to dynamical processes in both solid-state and liquid environments.
Short Biography
Valentin Freilikher is Professor of Physics at Bar-Ilan University, Israel, where he has served since 1991. He received his M.Sc. in Physics from Kharkov State University in 1966, his Ph.D. from the USSR Academy of Science in 1970, and the Senior Research Scientist degree from the same Academy in 1976. Before joining Bar-Ilan University, he worked at the Institute of Radiophysics and Electronics of the USSR Academy of Science. From 1993 to 2010, he was Head of the Microwave Remote Sensing Center at Bar-Ilan University. He has held visiting positions at the University of California, Irvine, the University of Twente, Galway University, Sydney University of Technology, and RIKEN Institute. Since 1999, he has been a member of the Editorial Board of Waves in Complex and Random Media. Prof. Freilikher has authored/co-authored more than 190 publications. Research Interest: interaction of electromagnetic radiation and quantum particles with disordered media inverse scattering problem random matrix theory theory of Non-Hermitian random systems micro-wave remote sensing.
