Luat T. Vuong

Plasmon-induced Lorentz forces of nanowire chiral hybrid modes

The mechanical forces associated with surface currents are widely overlooked and point to a new family of plasmonically-driven processes. Here, we investigate the Lorentz forces acting on a free electron gas that is bound to the surface of a nanowire. We demonstrate that appreciable mechanical forces are produced by longer illumination wavelengths between longitudinal and transverse absorption resonances via the excitation of chiral hybrid plasmon modes. We are the first to associate plasmonic activity as the underlying mechanism for nanowire rotation, which explains prior experimental results. The presence of chiral hybrid plasmon modes yields the greatest net translation and torque forces. The asymmetric plasmon behavior subsequently affects the complex nonlinear dynamics of plasmonic nonspherical nanoparticles in fluids.

Control of photo-induced voltages in plasmonic crystals via spin-orbit interactions

There is wide interest in understanding and leveraging the nonlinear plasmon-induced potentials of nanostructured materials. We investigate the electrical response produced by spin-polarized light across a large-area bottom-up assembled 2D plasmonic crystal. Numerical approximations of the Lorentz forces provide quantitative agreement with our experimentally-measured DC voltages. We show that the underlying mechanism of the spin-polarized voltages is a gradient force that arises from asymmetric, time-averaged hotspots, whose locations shift with the chirality of light. Finally, we formalize the role of spin-orbit interactions in the shifted intensity patterns and significantly advance our understanding of the physical phenomena, often related to the spin Hall effect of light.

Influence of solvent polarity on light-induced thermal cycles in plasmonic nanofluids

Pattern formation often reveals constituent nonlinear mechanisms of a complex system. Here, we study self-synchronizing, light-induced thermal cycles in plasmonically absorbing nanofluids, whose anomalous thermal, optomechanical, electrochemical, and hydrodynamic responses are not yet well understood. We show that the oscillatory behavior—caused by light grazing the nanofluid meniscus—exhibits a strong dependence on hydrogen bonding in the solvent environment and that there are low-intensity optical thresholds in alcohol–water binary-solvent nanofluids. Moreover, these thermal cycles occur with a periodic, vertically discharging heat-dissipation mechanism, which could be facilitated by nanobubbles or thermophoresis. We show that an incoherent white-light source, such as sunlight, will also induce self-synchronizing thermal cycles; in this demonstration, we illustrate new methods of energy storage, transfer, and harvesting that will not alter the natural carbon cycle of life.

Spontaneous light-driven heat cycles in metallic nanofluids with nanobubbles

We present the first experiments of spontaneous oscillatory behavior in binary-solvent nanofluids, which occurs when collimated light grazes menisci. The robust heat cycles identify nanobubbles, new mechanisms for probing nanoparticle-solvent chemistry, and novel thermo-mechanical dynamics.

Enhanced transverse photo-induced voltage by slow light

We demonstrate the presence of spin-polarized transverse voltage in a metal-dielectric two-dimensional photonic crystal in the visible regime and determine that the presence of slow light at the photonic band edge leads to voltage enhancement.

Robustness and spatial multiplexing via diffractal architectures

When plane waves diffract through fractal-patterned apertures, the resulting far-field profiles or diffractals also exhibit iterated, self-similar features. Here we show that this specific architecture enables robust signal transmission and spatial multiplexing: arbitrary parts of a diffractal contain sufficient information to recreate the entire original sparse signal.

Anomalously-large photo-induced magnetic response of disperse metallic nanocolloids

We demonstrate for the first time a plasmon-assisted magnetic response that occurs with disperse gold nanoparticles in aqueous solution. We observe increased Fano-like resonances and show the nonlinear interaction that occurs with matrix vortices.