Light induced shock wave interaction in opaque suspensions

TYPESolid State Institute Seminar
Speaker:Mr. Yoav Hazan
Affiliation:Physics Department and Solid State Institute, Technion
Time:12:30 - 13:30
Location:Solid State Auditorium(Entrance)
Abstract:To date, almost all the research in optofluidics and optical manipulation  of particles  in fluids  is  limited to
the regime of dilute  suspensions, where the light field  is  easily manipulated deep within the fluid because
the  suspension  is  so  dilute  that  scattering  can  be  neglected  altogether.  In  fact,  optical  manipulation  of
particles in opaque suspension was considered impossible up until 2013,  when a former student in our  group
has  demonstrated  optically-induced  shock-fronts  of  nanoparticles  propagating  deep  within  the  opaque
suspension, and light-induced phase transition in the regions where light has created very large concentration
of nanoparticles and transformed the suspensions  to a gel. That work has opened the door to the investigation
of light-fluid interaction in opaque fluids.
I  will  present  experiments  studding  the  nonlinear  interaction-collision  between  two  light-induced  shock
waves of nano-particles in highly scattering (opaque) suspensions. I will show that such collisions give rise
to  the formation of  gel domain walls between the shock waves. The interaction  is  dominated by the lateral
offset between the input beams and their  optical power. The interaction of  the  beams with  a lateral offset
creates shock-fronts, which transforms into unidirectional circulation whose direction is determined by the
lateral  offset.  For  a  centered  heads-on  collision  interaction,  the  shock  waves  give  rise  to  a  long-lived
transverse domain wall, which is sensitive to very small asymmetry in the input beams.