Dynamically Reconfigurable Bipolar Optical Gradient Force Induced by Mid‐Infrared Graphene Plasmonic Tweezers for Sorting Dispersive Nanoscale Objects

Abstract

Existing techniques for optical trapping and manipulation of microscopic objects, such as optical tweezers and plasmonic tweezers, are mostly based on visible and near‐infrared light sources. As it is in general more difficult to confine light to a specific length scale at a longer wavelength, these optical trapping and manipulation techniques have not been extended to the mid‐infrared spectral region or beyond. Here, it is shown that by taking advantage of the fact that many materials have large permittivity dispersions in the mid‐infrared region, optical trapping and manipulation using mid‐infrared excitation can achieve additional functionalities and benefits compared to the existing techniques in the visible and near‐infrared regions. In particular, it is demonstrated that by exploiting the exceedingly high field confinement and large frequency tunability of mid‐infrared graphene plasmonics, high‐performance and versatile mid‐infrared plasmonic tweezers can be realized to selectively trap or repel nanoscale objects of different materials in a dynamically reconfigurable way. This new technique can be utilized for sorting, filtering, and fractionating nanoscale objects in a mixture.

Nanoparticle Deep-Subwavelength Dynamics Empowered by Optical Meron–Antimeron Topology

“…High-precision sorting of gold nanoparticles (AuNPs) finds a diversity of applications in numerous areas due to their unique size-correlated optical and physical properties. , They are particularly critical in biological studies, such as photothermal therapy, drug delivery, and imaging. − AuNPs are usually synthesized using a chemical process, which results in a broad size distribution, severely hindering their performance. − It is of paramount importance to develop an efficient sorting scheme. Among all sorting approaches, including centrifugation, , acoustic sorting, electrophoresis, and microfluidics, , optical force-based sorting techniques have been demonstrated to be non-invasive and highly precise. − Most optical force strategies deal with single nanoparticles, such as optical chromatography, a phase gradient field, − plasmonic nanostructures, line-shaped beams, interference patterns, − and evanescence waves . Massive sorting can be realized with holographic optical tweezers, , an optical switch, microfluidics, silicon nanowaveguides, photonic crystals, etc.…”