Branched Flow of Light

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

When waves propagate through a homogeneous medium, they diffract and spread. However, when waves propagate through a smooth disordered medium, instead of producing completely random patterns, they form channels of enhanced intensity that keep diving as they propagate, forming a beautiful pattern resembling the branches of a tree. This fundamental wave phenomenon is known as branched flow and has been often overlooked. It was first observed for electrons, but it is a universal wave phenomenon that can occur for any kind of wave, from microwaves and light to sound and tsunami waves. This project will study new aspects of branched flow by studying light propagating in thin-liquid films. These explorations could not only improve our understanding of branched flow but potentially provide new insight on how to characterize and effectively transmit waves through smooth disordered media, such as light and sound waves through biological tissue or mechanical waves through disordered materials. This work will have a broad impact on the community by providing educational opportunities for students at the high school, undergraduate, and graduate levels. This project will investigate new aspects of the universal wave phenomenon of branched flow by bringing it to experimentally unexplored regimes. The PI and his undergraduate and graduate students will theoretically and experimentally study the propagation of laser beams inside thin liquid films – where the local thickness variations lead to a smoothly disordered effective index of refraction landscape that generates the branched flow of light. The research team will study branched flow in anisotropic and strongly disorder media to investigate how branched flow could be used to characterize such media. This project will experimentally study how to control branched flow by wavefront shaping to allow efficient energy transmission through smooth random media by exciting single branched flow channels. Finally, by studying how light interacts with a thin liquid film by radiation pressure, light absorption, and gradient forces, the research could open the door to possible applications of these interactions in optofluidic devices. The project objectives will be accomplished with graduate and undergraduate students by conducting multi-disciplinary research at the boundary between photonics and fluid mechanics, from theory and design to experimental observations. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.