Angular momentum of light has been applied to various applications such as mechanical motion manipulation, optical communication, and sensing. Furthermore, we have proposed that it is possible to form optical fields with angular momentum in nanometer scale area using plasmonic fields of multimer nanoantennas and have succeeded in experimentally manipulating orbital rotation of nanoparticles and controlling the chirality of crystals. However, the angular momentum of light is converted due to the interaction between light and matter in the process of transmission from incident lights to the plasmonic fields, and the laws of the conversion have not yet been clarified. To form plasmonic fields with the desired angular momentum on the nanometer scale, it is necessary to unveil thse conversion laws. Therefore, we analyzed the electromagnetic fields of the plasmonic fields of multimer nanoantennas and clarified the conversion law governing the spin and orbital angular momentum transfer. We also show that the interference of multiple fields with converted angular momentum enables the forming of nanometer scale fields with fractional angular momentum.
We design and fabricate triangular trimer gold nanostructures with two different edge lengths and investigate effects of plasmon modes on the crystallization behaviors induced by plasmonic optical trapping. The location of the enhanced electric field depends on the edge lengths (170 and 230 nm) of the triangular trimer. The crystallization of NaClO3 was induced by the 1064-nm laser irradiation on a single trimer structure. The generated crystal is attributed to be a metastable crystal with birefringence. Polymorphic transformation occurs in the case of continuous laser irradiation onto a 230 nm trimer, but intriguingly never in the case of a 170 nm trimer. These results will contribute to the understanding of the crystallization mechanism of NaClO3 by plasmonic trapping and give a novel insight to polymorphic transformation.
The spin angular momentum of light can induce the orbital rotation of matter via spin-orbit angular momentum conversion. In this work, we demonstrate the orbital rotation of nanoparticles using two different physical mechanisms. First, a nanoscale Poynting vector vortex is created above the nanogap of a plasmonic trimer nanoantenna upon circularly polarized laser irradiation. Using these trimer nanotweezers, single fluorescent nanodiamond trapping and rotation is experimentally achieved. Second, the orbital rotation of VO2 nanoparticles is achieved using a focused, circularly polarized Gaussian laser beam. We demonstrate that the non-linear optical response caused by the insulator-to-metal phase transition of VO2 leads to the formation of an annular trapping potential well around the center of the laser beam.
The ability to control nanoscale motions of nanomaterials is expected to play significant roles in various fields such as photophysics, photochemistry and biological applications. For the optical nanomanipulation, metal nanoantenna structures are widely used. These plasmonic structures can confine light into nano-sized volumes and enhance the nanoscale light-matter interactions. In this paper, we demonstrated that precise orbital rotational motion is driven by the angular momentum that is transferred from photon to plasmonic nanoantenna. We present the numerical simulation results and discussion on the mechanism of the angular momenta transfer. Then, we show the experimental results on the rotational manipulation of a nanodiamond using plasmonic trimer structure.
While optical forces could be used to select and sieve nanoparticles based on their optical properties, their mechanical
action is usually too weak to overcome the fast Brownian diffusion of nanoparticles dispersed in a liquid phase. Among
various theoretical proposals and experimental realizations of optical sorting techniques, glass capillaries with micrometer
or submicrometer diameters offer a promising approach to achieve efficient optical sorting of nanoparticles. By confining
dispersed nanoparticles into the light path over few-millimeter-long distances, it provides enough time/distance for weak
optomechanical interactions to affect the motion and the concentration of nanoparticles at the macroscopic scale. In this
work, we report on our recent experimental results.
Plasmonic nanotweezers are renowned tools for trapping and handling nanoparticles via near-field optical forces. In
this work, we investigate the optical trapping of polymer beads using plasmonic nanotweezers integrated on a hybrid
photonic–plasmonic chip. A periodic chain of gold nanorods coupled to a silicon photonic waveguide is used to trap
single beads as well as self-assembled bead clusters. We evaluate the trapping efficiency and the trapping potential of the
nanotweezers by particle tracking and statistical analysis. Vacancy-free clusters composed of four and seven beads are
found to be the most stable due to the simultaneous actions of both optical and electrostatic forces. Those results evidence
the role of plasmonic nanotweezers for efficient particle assembly and manipulation at the nanoscale in future lab-on-achip
applications.
Tapered glass capillaries can be fabricated having cross-sections only few square-micrometers large. Efficient light focusing and guiding in thin, millimeter-long capillaries filled with a liquid solution provides competitive advantages for the optical sorting of nanoparticles. In this work, optical transport of fluorescent nanodiamonds is demonstrated both in water and DMSO. Size-dependent sorting of a large amount of nanodiamonds is also achieved using a backward liquid flow. An analytical model is used to calculate the femtonewton-scale forces acting on the particles and evaluate the sorting efficiency of tapered capillaries.
Integration of plasmonic nanotweezers on silicon chips holds promise for many lab-on-a-chip applications. In this work, optical trapping of single beads and self-assembled clusters composed of up to nine beads is achieved using plasmonic nanotweezers fabricated on a silicon nanophotonic waveguide. We statistically analyze the preferred orientations, the probability of occurrence and the stability of the different cluster configurations. We evidence that the presence of two potential barriers along the waveguide edges results in the enhanced stability of some specific cluster configurations. Our results pave the way for further development of hybrid plasmonic-photonic nanotweezers and lab-on-chips.
In this work, we explore a new bottom-up approach based on plasmon-assisted hydrothermal synthesis (PAHS) to achieve localized growth of zinc oxide (ZnO) in hybrid nanophotonic devices. By engineering gold nanogap antennas, we achieve efficient control over the localization and enhancement of both the electric field and the generated heat. A nanobutterfly antenna is designed to achieve both polarization-dependent heat localization and localized electric field enhancement. A few-nm-thick ZnO layer is grown at the targeted location of the nanogap antenna thanks to selective plasmonic heating. We also numerically study the back-action induced by the material synthesis on the heat generated by the antenna and show how PAHS can be used as a self-limited growth method. The PAHS method opens new perspectives for the design and fabrication of hybrid nanophotonic devices.
While optical forces may provide very efficient techniques to manipulate and sort nanomaterials according to their optical properties, experimental realizations remain challenging. In most cases, the key issue lies in the imbalance between the fast Brownian diffusion of nanoscale objects and the weak, localized effect of optical forces. We propose here a new approach based on tapered glass capillaries with only few-μm2-large cross-section areas. The transparent pipe-like structure of tapered glass capillaries allows for simultaneously confining and guiding both the light and the liquid solution in a narrow, few-mm-long optofluidic channel. In this work, a tapered glass capillary is filled with a liquid dispersion of fluorescent nanodiamonds, cleaved, and sealed. Light from a green laser source is then coupled to one end of the capillary. Optical transport of nanodiamonds is observed by fluorescence microscopy. Velocities of nanodiamonds reaching few tens of micrometers per second are measured at the waist of the tapered capillary. In the presence of a liquid flow inside the optofluidic channel, size-dependent sorting of a large ensemble of nanodiamonds is demonstrated. Based on an analytical model, we evaluate the influence of the nanodiamonds’ size on both the optical and the hydrodynamic drag forces acting on the nanoparticles. Our results show that tapered glass capillaries provide a suitable optofluidic platform to achieve efficient optical sorting of nanoparticles by exploiting optical forces as weak as few femtonewtons.
Optical forces may provide an elegant solution to achieve optical sorting of nanoparticles according to their optical properties. Yet, efficient nanoparticle optical sorting would require all the nanoparticles to be gathered and kept inside the light path for a sufficient time. In order to overcome nanoparticle diffusion, we investigate the use of tapered glass capillaries as optofluidic waveguides. We demonstrate size-dependent optical transport of fluorescent nanodiamonds inside a tapered capillary. Particle velocities reaching few tens of micrometers per second were achieved, and size estimations are performed based on the nanoparticles’ velocities. Nanoparticle sorting is also demonstrated by balancing the optical transport of the nanodiamonds with a liquid flow in the opposite direction.
Metallic nanostructures can be designed to act not only as nanoscale optical antenna but also as much localized heat sources. Although both aspects are usually independently investigated, we conduct here a multiphysics approach to design multipurpose plasmonic nanogap antennas. On the one hand, by mean of a hydrothermal synthesis reaction, we make use of the localized heat production to control the growth of a ZnO layer at the surface of the targeted part of a gold nanoantenna. On the other hand, the fabricated hybrid plasmonic-photonic nanoantenna allows for large electric field enhancement inside ZnO-filled plasmonic nanogaps. Such nanodevice could find application as nanoscale light source.
KEYWORDS: Deposition processes, Nanoantennas, Molecules, Scanning electron microscopy, Gold, Luminescence, Near field optics, Nanoparticles, Plasmonics
In this work, we demonstrate an original single-nanoparticle deposition process based on near-field optical forces
arising from much localized plasmonic resonant gap-mode. At first, nanoparticles exclusively made of fluorescent dye
molecules are fabricated in aqueous colloidal suspension. Near-field optical forces are then used to attract and deposit
single nanoparticles in the nanogap of plasmonic nanoantennas. This one-step deposition process allows targeted
deposition of nanoscale materials directly from a colloidal dispersion to a few-nanometer large area of interest.
Near-field optical forces arise from evanescent electromagnetic fields and can be advantageously used for on-chip
optical trapping. In this work, we investigate how evanescent fields at the surface of photonic cavities can efficiently trap
micro-objects such as polystyrene particles and bacteria. We study first the influence of trapped particle’s size on the
trapping potential and introduce an original optofluidic near-field optical microscopy technique. Then we analyze the
rotational motion of trapped clusters of microparticles and investigate their possible use as microfluidic micro-tools such
as integrated micro-flow vane. Eventually, we demonstrate efficient on-chip optical trapping of various kinds of bacteria.
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