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Appropriate combinations of laser beams can be used to trap and manipulate small particles with optical tweezers as well as to induce significant optical binding forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals and, in general, Casimir–Lifshitz interactions between neutral bodies arising from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations. Here we show, both theoretically and experimentally, that dispersion forces between small colloidal particles can also be induced and controlled using artificially created fluctuating light fields. Using optical tweezers as a gauge, we present experimental evidence for the predicted isotropic attractive interactions between dielectric microspheres induced by laser-generated, random light fields. These light-induced interactions open a path towards the control of translationally invariant interactions with tuneable strength and range in colloidal systems. Natural dispersion forces acting between molecules and particles arise from electromagnetic fields generated by quantum and thermal fluctuations. Here, Brügger et al. show that isotropic dispersion forces between colloidal particles can be induced, controlled and tuned with artificial, fluctuating laser light fields.

Disordered dielectric materials with structural correlations show unconventional optical behavior: They can be transparent to long-wavelength radiation, while at the same time have isotropic band gaps in another frequency range. This phenomenon raises fundamental questions concerning photon transport through disordered media. While optical transparency in these materials is robust against recurrent multiple scattering, little is known about other transport regimes like diffusive multiple scattering or Anderson localization. Here, we investigate band gaps, and we report Anderson localization in 2D disordered dielectric structures using numerical simulations of the density of states and optical transport statistics. The disordered structures are designed with different levels of positional correlation encoded by the degree of stealthiness χ. To establish a unified view, we propose a correlation-frequency (χ–ν) transport phase diagram. Our results show that, depending only on χ, a dielectric material can transition from localization behavior to a band gap crossing an intermediate regime dominated by tunneling between weakly coupled states.

In the current context of the Internet of Things, embedded devices can have some intelligence and distribute both data and processed information. This article presents the paradigm shift from a hierarchical pyramid to an inverted pyramid that is the basis for edge, fog, and cloud-based architectures. To support the new paradigm, the article presents a distributed modular architecture. The devices are made up of essential elements, called control nodes, which can communicate to enhance their functionality without sending raw data to the cloud. To validate the architecture, identical control nodes equipped with a distance sensor have been implemented. Each module can read the distance to each vehicle and process these data to provide the vehicle’s speed and length. In addition, the article describes how connecting two or more CNs, forming an intelligent device, can increase the accuracy of the parameters measured. Results show that it is possible to reduce the processing load up to 22% in the case of sharing processed information instead of raw data. In addition, when the control nodes collaborate at the edge level, the relative error obtained when measuring the speed and length of a vehicle is reduced by one percentage point.

Diffraction-free light-sheet beams, strongly confined in one axis, are typically thought to self-bend during propagation in free space and cannot be made flat. Now, diffraction-free planar light sheets in air have been realized by exploiting polychromatic pulsed beams.

Spin-dependent lateral optical forces, 100,000 times larger than those reported so far, can lead to displacements of centimetre-sized objects observable by the naked eye.

Improvements in electrostatic force microscopy now make it possible to measure the dielectric constant of isolated low-polarizable nanoparticles and viruses, thus enabling the label-free identication of dielectric nanomaterials of similar morphology. Biological nanoparticles in an aqueous environment are often modelled as a low-dielectric core surrounded by a high-dielectric solvent, and their characterization is most often done by dielectrophoresis.

Lateral optical forces induced by linearly polarized laser beams have been predicted to deflect dipolar particles with opposite chiralities toward opposite transversal directions. These “chirality-dependent” forces can offer new possibilities for passive all-optical enantioselective sorting of chiral particles, which is essential to the nanoscience and drug industries. However, previous chiral sorting experiments focused on large particles with diameters in the geometrical-optics regime. Here, we demonstrate, for the first time, the robust sorting of Mie (size ~ wavelength) chiral particles with different handedness at an air–water interface using optical lateral forces induced by a single linearly polarized laser beam. The nontrivial physical interactions underlying these chirality-dependent forces distinctly differ from those predicted for dipolar or geometrical-optics particles. The lateral forces emerge from a complex interplay between the light polarization, lateral momentum enhancement, and out-of-plane light refraction at the particle-water interface. The sign of the lateral force could be reversed by changing the particle size, incident angle, and polarization of the obliquely incident light.Optical sorting: Forcing mirror-image microparticles to go their own wayA setup that uses lasers to automatically sort compounds with nearly imperceptible chemical differences could improve the efficiency of drug manufacturing. Many pharmaceuticals are difficult to purify because they are chiral, meaning they exist as one of two mirror-image structures that rotate in opposite directions under linearly polarized light. Cheng-Wei Qiu from the National University of Singapore and colleagues now report that lateral forces generated by a mix of reflected and refracted light rays can separate chiral microspheres floating on the surface of water. The team developed a line-shaped optical trap to hold a mix of chiral particles in place, and then directed a polarized laser beam into the trap. Microscopic imaging revealed that particles with identical chirality moved laterally when exposed to the beam, with velocities dependent on incident angle and microparticle size.

Magnetodielectric small spheres present unusual electromagnetic scattering features, theoretically predicted a few decades ago. However, achieving such behaviour has remained elusive, due to the non-magnetic character of natural optical materials or the difficulty in obtaining low-loss highly permeable magnetic materials in the gigahertz regime. Here we present unambiguous experimental evidence that a single low-loss dielectric subwavelength sphere of moderate refractive index ( n =4 like some semiconductors at near-infrared) radiates fields identical to those from equal amplitude crossed electric and magnetic dipoles, and indistinguishable from those of ideal magnetodielectric spheres. The measured scattering radiation patterns and degree of linear polarization (3–9 GHz/33–100 mm range) show that, by appropriately tuning the a/λ ratio, zero-backward (‘Huygens’ source) or almost zero-forward (‘Huygens’ reflector) radiated power can be obtained. These Kerker scattering conditions only depend on a/λ . Our results open new technological challenges from nano- and micro-photonics to science and engineering of antennas, metamaterials and electromagnetic devices. The absence of forward or backward scattered radiation by magnetodielectric spheres was predicted decades ago, yet direct measurements have remained elusive. Geffrin et al . present unambiguous evidence of such scattering effects in the gigahertz range for a sub-wavelength dielectric sphere.

Scientists have theoretically proposed that it is possible to pull objects from a far distance towards a light source in the absence of axial optical gradient forces.