Optical Matter 
Research QuestionsWhat is a good order parameter or description of the excitations created by single colloids dragged through a dense colloidal fluid?
Can the fluctuations in driven non-equilibrium systems be related to fluctuations in the undriven equilibrium system?
Can we tailor the strength of optical matter interactions so as to transition from a fluid to jammed or solid-like material?
Optical matter is an interesting medium that allows visualizing phenomena that are analogous to molecular liquids yet can be tuned by density or confinement or interaction strength to (perhaps) allow insights into glassy or jammed materials. We create nonequilibrium perturbations in such fluids and use optical microscopy/imaging to measure the response(s) of the colloids that are the "bath." In addition to finding long range "dipolar" excitations that are evident in the ensemble responses elicited from dragging single particles, we have also identified force-chain excitations and are relating the measured forces on the optically trapped particle to both the force chain properties and those of the void volume (or hole) left in its wake. We are working on simulation approaches to understand the relation of these nonequilibrium force chains to spontaneous equilibrium fluctuations and thus to ascertain whether the nonequlibrium experimental approach is a way to create and measure what would be rare events. Finally, we are using focused laser-induced tuning of local optical matter interaction potentials to create active materials.
Experimental setup and data for pulling a single particle through a dense colloidal fluid.