"Aspects of light-fluid interaction: Optical Manipulation in Densely Scattering Opaque Suspensions"

TYPESolid State Institute Seminar
Speaker:Mr. Elad Greenfield
Affiliation:Physics Department and Solid State Institute, Technion
Location:Solid State Auditorium(Entrance)
Remark:Ph.D. Student of Distinguished Professor Moti Segev
Abstract:Optofluidics, the science of light interaction with fluids, presents a host of attractive and versatile
alternatives to traditional technologies. Optofluidic effects rely heavily on the ability to tailor th e
distribution of the optical fields and forces inside particulate-liquid suspensions, with micron scale
accuracy. However, densely-packed suspensions of particles, ranging from biological suspensions such as
blood, plasma, natural minerals, milk and foods, to synthetic nanoparticle-based drugs, polluted fluids, inks
and paints- are inaccessible to optical manipulation. These suspensions scatter the light so heavily that they
become opaque: the light diffuses, losing its directionality and localization, and the optical field cannot be
externally tailored inside such suspensions.

In my thesis, I focus on nonlinear light-fluid interactions. The talk will begin with some brief examples of
linear and nonlinear tools for optical manipulation of fluids that were developed as a part of my thesis. The
bulk of the talk will focus on theoretical and experimental optical manipulation of the local properties of
particulate-loaded, scattering (opaque) suspensions. We show that counter-intuitively, optical forces that
multiply-scattered light exerts on the same particles that scatter the light- can give rise to dense shock
fronts of particle concentration, propagating deep inside the opaque suspensions. We explore these waves
theoretically and experimentally, and exploit them to manipulate the local properties of opaque fluids. We
demonstrate optical transport and concentration of large populations of nanoparticles, clearing of localized
volumes of opaque solutions from particles, generation of directional light-matter filaments, and light
induced suspension-to-gel phase transitions in localized volumes inside scattering fluids. These optofluidic
effects penetrate deep into the suspensions, constituting first evidence that light that scatters in fluidic
medium can give rise to localized, directional, and hence- 'anti-diffusive' fluidic effects. Further, this is a
first demonstration of light manipulating the local properties of multiply-scattering fluids. Possible
applications of this work are briefly discussed.