Generalization of the coupled dipole method to periodic structures

We present a generalization of the coupled dipole method to the scattering of light by arbitrary periodic structures. This new formulation of the coupled dipole method relies on the same direct-space discretization scheme that is widely used to study the scattering of light by finite objects. Therefore, all the knowledge acquired previously for finite systems can be transposed to the study of periodic structures.Comment: 5 pages, 2 figures, and 1 tabl

Selective nanomanipulation using optical forces

We present a detailed theoretical study of the recent proposal for selective nanomanipulation of nanometric particles above a substrate using near-field optical forces [Chaumet {\it et al.} Phys. Rev. Lett. {\bf 88}, 123601 (2002)]. Evanescent light scattering at the apex of an apertureless near-field probe is used to create an optical trap. The position of the trap is controlled on a nanometric scale via the probe and small objects can be selectively trapped and manipulated. We discuss the influence of the geometry of the particles and the probe on the efficiency of the trap. We also consider the influence of multiple scattering among the particles on the substrate and its effect on the robustness of the trap.Comment: 12 pages, 17 figure

Inverse scattering for reflection intensity phase microscopy

Reflection phase imaging provides label-free, high-resolution characterization of biological samples, typically using interferometric-based techniques. Here, we investigate reflection phase microscopy from intensity-only measurements under diverse illumination. We evaluate the forward and inverse scattering model based on the first Born approximation for imaging scattering objects above a glass slide. Under this design, the measured field combines linear forward-scattering and height-dependent nonlinear back-scattering from the object that complicates object phase recovery. Using only the forward-scattering, we derive a linear inverse scattering model and evaluate this model's validity range in simulation and experiment using a standard reflection microscope modified with a programmable light source. Our method provides enhanced contrast of thin, weakly scattering samples that complement transmission techniques. This model provides a promising development for creating simplified intensity-based reflection quantitative phase imaging systems easily adoptable for biological research.https://arxiv.org/abs/1912.07709Accepted manuscrip

Optical binding of magnetodielectric Rayleigh particles

We present a theoretical and numerical study of the optical binding and optical torque between two Rayleigh particles with arbitrary, complex, scalar dielectric permittivity and magnetic permeability. We use a computational approach based on the discrete dipole approximation to derive the optical force and torque experienced by the particles when illuminated by a linearly or circularly polarized plane wave. We show that optical binding between magnetodielectic particles is qualitatively different from the traditional case involving dielectric particles only. In particular, we show that for certain configurations, the system of two magnetodielectric particles will experience a long-range optical torque whose amplitude envelope does not decay with the separation between the particles. © 2013 American Physical Society

Efficient wPINN-Approximations to Entropy Solutions of Hyperbolic Conservation Laws

We consider the approximation of weak solutions of nonlinear hyperbolic PDEs using neural networks, similar to the classical PINNs approach, but using a weak (dual) norm of the residual. This is a variant of what was termed "weak PINNs" recently. We provide some explicit computations that highlight why classical PINNs will not work well for discontinuous solutions to nonlinear hyperbolic conservation laws and we suggest some modifications to the weak PINN methodology that lead to more efficient computations and smaller errors

CLS-CAD: Synthesizing CAD Assemblies in Fusion 360

The CAD design process includes a number of repetitive steps when creating assemblies. This issue is compounded when engineering whole product lines or design families, as steps like inserting parts common to all variations, such as fasteners and product-integral base parts, get repeated numerous times. This makes creating designs time-, and as a result, cost-intensive. While many CAD software packages have APIs, the effort of creating use-case specific plugins to automate creation of assemblies usually outweighs the benefit. We developed a plugin for the CAD software package "Fusion 360" which tackles this issue. The plugin adds several graphical interfaces to Fusion 360 that allow parts to be annotated with types, subtype hierarchies to be managed, and requests to synthesize assembly programs for assemblies to be posed. The plugin is use-case agnostic and is able to generate arbitrary open kinematic chain structures. We envision engineers working with CAD software being able to make designed parts reusable and automate the generation of different design alternatives as well as whole product lines

Optical forces from an evanescent wave on a magnetodielectric small particle

We report the first study on the optical force exerted by an evanescent wave on a small sphere with both electric and magnetic response to the incident field, immersed in an arbitrary nondissipative medium. New expressions and effects from their gradient, radiation pressure, and curl components are obtained due to the particle induced electric and magnetic dipoles, as well as to their mutual interaction. We predict possible dramatic changes in the force depending on either the host medium, the polarization and the nature of the surface wave

Optical binding of particles with or without the presence of a flat dielectric surface

Optical fields can induce forces between microscopic objects, thus giving rise to new structures of matter. We study theoretically these optical forces between two spheres, either isolated in water, or in presence of a flat dielectric surface. We observe different behavior in the binding force between particles at large and at small distances (in comparison with the wavelength) from each other. This is due to the great contribution of evanescent waves at short distances. We analyze how the optical binding depends of the size of the particles, the material composing them, the wavelength and, above all, on the polarization of the incident beam. We also show that depending on the polarization, the force between small particles at small distances changes its sign. Finally, the presence of a substrate surface is analyzed showing that it only slightly changes the magnitudes of the forces, but not their qualitative nature, except when one employs total internal reflection, case in which the particles are induced to move together along the surface.Comment: 8 pages, 9 figures, and 1 tabl

Coupled-dipole method in time domain

We present a time-domain formulation of electrodynamics based on the self-consistent derivation of the electromagnetic field in a linear, dispersive, lossy object via the coupled dipole method. © 2008 Optical Society of America