We demonstrate, for the first time, 2-dimensional (2D) direct print of perfect circle microdots consisting of close-packed Au nanoparticles by employing the optical vortex induced forward transfer (OV-LIFT). Going beyond the ink-jet printing technology, the OV-LIFT allows the direct print of ultrafine microdots with a diameter of ~8 μm and an ultralow positional error of <7 μm.
Optical vortex laser-induced forward transfer (OV-LIFT), in which light field with a helical wavefront is employed instead of a plane wave, enables the high-definition direct print of a variety of donor materials with high spatial resolution, however, its mechanism has not been fully understood yet. We herein demonstrate, for the first time, the numerical simulation model of OV-LIFT based on the simulation technique of thermo-fluid dynamics, including mass transport equation. Temporal evolution of the droplet ejection by the illumination of optical vortex pulse is successfully reproduced. Such numerical simulation model will enable the further improvements of OV-LIFT performances to develop advanced direct print technology for printed electronics, photonics and biotechnology.
We demonstrate the direct print of micron-scale dots consisting of close-packed gold nanoparticles by employing the optical vortex laser-induced forward transfer technology. Moreover, SAM enhances the close-packing of gold nanoparticles in the printed dot.
We numerically investigate the convection of surrounding fluid in optical trapping of micro- and nanoparticles. The
effects of the laser irradiation on the fluid simulation are twofold. First, we take into account the temperature increase of
the fluid due the photothermal effect of the solvent, that is, the fluid flow is described by the Navier-Stokes equations
under the Boussinesq approximation. Second, we assume that the suspended particles drag the fluid when they are
transported by the optical force. This dragging effect is considered in the fluid simulation by adding to the Navier-Stokes
equation an external forcing term, which is modelled by considering the counterbalance between the optical scattering
force and the Stokes drag. It is shown that the latter effect is dominant under the usual experimental setup in optical
trapping of particles with the diameter larger than 0.5 μm. Furthermore, the particle size dependence on the convective
flow speed is investigated. The numerical results are supported by optical trapping experiment qualitatively.
We demonstrate the creation of a microdroplet with a plasmonic Au nanoparticle core by employing the optical vortex
laser-induced forward transfer technology. The single plasmonic nanoparticle in the microdroplet is printed as a plasmonic
nanocore on a receiver substrate with a spatial resolution beyond the diffraction limit. This phenomenon manifests that the
optical vortex traps three-dimensionally only a suspended single Au nanoparticle in its dark core by its repulsive force
owing to plasmonic resonance, and it has the potential to realize a myriad of plasmonic structured materials.
Plasmonic nanostructures enable us to enhance light fields at nanoscale beyond diffraction limit, thereby offering us metamaterials and plasmonic crystals to realize exotic light-matter interactions, including negative refractive index, invisible cloaking, and perfect absorption.
We here demonstrate, for the first time to be the best of our knowledge, the creation of a single water microdroplet with a single plasmonic Au nanoparticle (~150 nm) core (plasmonic nanocore) by employing the optical vortex induced forward transfer. The microdroplet can be easily trapped to form a single plasmonic nanocore on a receiver substrate with a spatial resolution beyond the diffraction limit. Going beyond conventional fabrication processes for plasmonic structures, such as lithography technologies based on electron and ion beams, such plasmonic nanocore formation in a water microdroplet should offer us new fabrication technology for plasmonic structures.
Micro- and nanoparticles in a solution under the irradiation of an optical vortex are considered using a mathematical model based on fluid mechanics. The particles exhibit an inherent Brownian motion due to their small sizes. In particular, we consider the case of plural particles trapped in the orbit of the optical vortex expressed by the Laguerre-Gaussian beam. The inter-particle interaction includes not only repulsive forces between the particles but also the forces arising from a hydrodynamic effect. To be more specific, the flow of a solvent induced by the motion of a particle affects the motion of the other particles. The numerical simulation of the model shows that the orbital speed of the particles increases as the number of particles in the orbit.
Quantitative evaluation of optical forces on nanoscale objects caused by optical vortices is significant for application of optical vortex to nanotechnology. In this study, we analyze an orbital motion of single gold nanoparticles with a diameter of 150 nm driven by the Laguerre-Gaussian beam. A nanofluidic channel with a height of 300 nm is used to confine the orbital motion into two-dimensional plane by restricting their Brownian motion perpendicular to a focal plane of objective lens, resulting in the visualization by dark-field microscopy. A particle tracking analysis of the acquired images allows the quantitative evaluation of optical forces, such as trapping stiffness and driving force of the orbital motion, and show a reasonable agreement with a theoretical estimation.
When nanoparticles are exposed to an optical field with orbital angular momentum, that is optical vortex, such particles are swirled around optical axis. Although such a phenomenon was observed experimentally, theoretical and numerical approaches have not been developed enough. In this study, we propose a numerical model for dynamical motions of a single nanoparticle. Based on Rayleigh scattering regime, the gradient force which dominantly acts on a nanoparticle is computed. The gradient force is usually derived from time averaged electric field and then, a tangential component is vanished. Herein, we carefully treat the tangential term by using time dependent electromagnetic fields. Consequently, it is found that a tangential component in the gradient force induce swirling motions of a nanoparticle.
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