Optical ordering of nanoparticles trapped by Laguerre-Gaussian laser modes

Abstract

In earlier work, it has been established that laser-induced coupling between a pair of nanoparticles can enable the generation of novel patterns, entirely determined and controlled by the frequency, intensity, and polarization of the optical input. In this paper, the detailed spatial disposition about the beam axis is determined for two-, three-and fournanoparticle systems irradiated by a Laguerre-Gaussian (LG) laser mode. The range-dependent laser-induced energy shift is identified by the employment of a quantum electrodynamical description, calculations are performed to determine the distribution of absolute minima as a function of the topological charge, and the results are graphically displayed. This analysis illustrates a number of interesting features, including the fact that on increasing the LG beam's topological charge the particles increasingly cluster, i.e. the order of the structure is significantly raised -also the number of minima for which the particles can be trapped is enhanced. Finally, it is shown that similar principles apply to other kinds of radially structured optical modes.

Multiple optical trapping and binding: new routes to self-assembly

“…where f lp and A lp are standard LG beam functions as defined in [146], and α 0 is the polarizability of each spherical nanoparticle, φ is the angle between the polarization of the ABC against ψ 1 (x-axis) and ψ 2 (y-axis) for three particles in an LG beam with l = 20; lighter shading denotes higher values of E 0 ABC . Adapted from [143][144][145] input radiation and R and ψ is the azimuthal displacement angle. In the short-range region (kR 1), the leading term of equation ( 20) is determined from Taylor series expansions of sin(kR) and cos(kR).…”

“…(a) Geometry of a particle pair in a Laguerre-Gaussian beam (p = 0); (b) Clustering of nanoparticles in an LG beam; (c) Contour graphs of E 0ABC against ψ 1 (x-axis) and ψ 2 (y-axis) for three particles in an LG beam with l = 20; lighter shading denotes higher values of E 0 ABC . Adapted from[143][144][145]…”

Optically induced inter-particle forces: from the bonding of dimers to optical electrostriction in molecular solids

“…More specifically, when any particles are held at equilibrium in an optical trap or tweezers set-up, the small optically induced forces that also operate may be sufficient to produce observable departures from the behaviour expected of independent particles. In some earlier work, it has already been shown that a weak binding effect can in some cases lead to optical clustering and in others to pattern formation [42].…”