Series expressions for the net radiation force and torque for a spherical particle illuminated by an arbitrarily defined monochromatic beam are derived utilizing the spherical-particle/arbitrary-beam interaction theory developed in an earlier paper. Calculations of net force and torque are presented for a 5-μm-diam water droplet in air optically levitated by a tightly focused (2 μm beam waist diameter) TEM00-mode argon-ion (λ=0.5145 μm) laser beam for on and off propagation axis, and on and off structural resonance conditions. Several features of these theoretical results are related to corresponding experimental observations.

A high-performance magnetic shield with large length-to-diameter ratio Rev. Sci. Instrum. 83, 065108 (2012) Radiation and near field in resistance-inductor circuit transients J. Appl. Phys. 111, 114907 (2012) Loss characterization of Mo-doped FeNi flake for DC-to-DC converter and MHz frequency applications J. Appl. Phys. 111, 07E329 (2012) The electron cyclotron resonance ion source with arc-shaped coils concept (invited) Rev. Sci. Instrum. 83, 02A312 (2012) Additional information on J. Appl. Phys.Theoretical expressions for the internal and external electromagnetic fields for an arbitrary electromagnetic beam incident upon a homogeneous spherical particle are derived, and numerical calculations based upon this theoretical development are presented. In particular, spatial distributions of the internal and near-surface electric field magnitude (source function) for a focused fundamental (TEMoo mode) Gaussian beam of 1.06.urn wavelength and 4.urn beam waist diameter incident upon a 5-,um-diam water droplet in air are presented as a function of the location of the beam focal point relative to the sphere center. The calculations indicate that the internal and near-surface electric field magnitude distribution can be strongly dependent upon relative focal point positioning and may differ significantly from the corresponding electric field magnitude distribution expected from plane-wave irradiation.

The spherical particle/arbitrary beam interaction theory developed in an earlier paper is used to investigate the dependence of structural resonance behavior on focal point positioning for a spherical particle illuminated by a tightly focused (beam diameter less than sphere diameter), linearly polarized, Gaussian-profiled laser beam. Calculations of absorption efficiency and distributions of normalized source function (electric field magnitude) are presented as a function of focal point positioning for a particle with a complex relative index of refraction of n̄=1.33+5.0×10−6i and a size parameter of α≊29.5 at both nonresonance and resonance conditions. The results of the calculations indicate that structural resonances are not excited during the on-center focal point positioning of such a tightly focused beam but structural resonances can be excited by proper on-edge focal point positioning. Electric wave resonances were found to be excited by moving the focal point from on-center towards the edge of the sphere parallel to the direction of the incident beam electric field polarization. Magnetic wave resonances were found to be excited by moving the focal point from on-center towards the edge of the sphere perpendicular to the direction of the incident beam electric field polarization.

Through an application of our previously derived single spherical particle-arbitrary beam interaction theory, an iterative procedure has been developed for the determination of the electromagnetic field for a beam incident on two adjacent spherical particles. The two particles can differ in size and composition and can have any positioning relative to each other and relative to the focal point and propagation direction of the incident beam. Example calculations of internal and near-field normalized source function ( approximately |E|(2)) distributions are presented. Also presented are calculations demonstrating the effect of the relative positioning of the second adjacent particle on far-field scattering patterns.

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