Long-distance optical pulling of nanoparticle in a low index cavity using a single plane wave

Abstract

Optical pulling force (OPF) can make a nanoparticle (NP) move against the propagation direction of the incident light. Long-distance optical pulling is highly desired for nano-object manipulation, but its realization remains challenging. We propose an NP-in-cavity structure that can be pulled by a single plane wave to travel long distances when the spherical cavity wrapping the NP has a refractive index lower than the medium. An electromagnetic multipole analysis shows that NPs made of many common materials can receive the OPF inside a lower index cavity. Using a silica-Au core-shell NP that is encapsulated by a plasmonic nanobubble, we experimentally demonstrate that a single laser can pull the Au NP-in-nanobubble structure for ~0.1 mm. These results may lead to practical applications that can use the optical pulling of NP, such as optically driven nanostructure assembly and nanoswimmers.

Optically Driven Gold Nanoparticles Seed Surface Bubble Nucleation in Plasmonic Suspension

“…Our previous studies have found that CS NPs in a suspension can be driven by dispersive optical scattering force originated from the momentum exchange between incident photons and the NPs (42,43). The photon stream in the laser beam usually exerts an optical pushing force that drives the CS NPs to move in the light propagating direction.…”

“…However, as reported in several previous works (43)(44)(45)(46)(47)(48)(49)(50), plasmonic vapor nanobubbles can be formed around the heated CS NPs irradiated by a pulsed laser at the SPR peak of the NPs. This supercavitation (i.e., nanobubble encapsulating the NP) can optically couple to the encapsulated NP to trigger the "negative" optical scattering forces on the NP, leading to an optical pulling force (Figure 2c), depending on the position of a CS NP inside the nanobubble (42,43). It means that the laser beam can drive the CS NP to move against the photo stream, and this is why some NPs are seen moving against the light propagation direction towards the BF surface.…”

“…High-speed videography reveals that the lightguided NP deposition on the surface is a necessity for bubble nucleation, and it is the optical dispersive force that drives such deposition. Optical pulling force is needed to deposit NPs on the BF surface, and this is achieved only when the laser intensity is sufficiently high to generate a supercavitating nanobubble around the NP, which is necessary to enable the proper optical condition for optical pulling motion to happen (42). On the FF surface, the optical pushing force, which exists on both bare or supercavitating NPs, makes the NP deposition easier and thus lowers the surface bubble nucleation threshold.…”

An Optical Cluster: Near‐Field Optical Sorting and Separation of Plasmonic, Dielectric, and Chiral Nanoparticle

“…Previously, such calculations of optical forces were done using this well‐known commercial software, COMSOL Multiphysics 5.3a in refs. [12,13,34,43].…”

“…However, nowadays the counter‐intuitive idea of optical pulling force has attracted much attention due to its exceptional nature of pulling the objects toward the light source using the scattering force [ 22,28–33 ] of light instead of the light intensity/“local” gradient force of light. This effect has been termed as the optical tractor beam effect, [ 28–30 ] which has recently been applied for long‐distance pulling [ 34,35 ] (not possible by gradient force). However, optical pulling force cannot be created on a usual dielectric Rayleigh‐sized object illuminated by a single plane wave, [ 30 ] i.e., nonstructured light.…”