Wide-field interferometric measurement of a nonstationary complex coherence function.

Spatial coherence function (SCF) is a complex function of two spatial coordinates that, in general, carries more information than the bare intensity distribution. A fast and quantitatively accurate measurement of the SCF is extremely important for a range of applications in optical sensing and imaging. Here, we demonstrate an efficient two-step procedure for measuring the full-field complex coherence function.

Babinet's principle for mutual intensity.

In classical diffraction theory, Babinet's principle relates the electromagnetic fields produced by complementary sources. This theorem was always formulated for single-point quantities, both intensities or field amplitudes, in conditions where the full spatial coherence is implicitly assumed. However, electromagnetic fields are, in general, partially coherent, and their spatial properties are described in terms of two-point field-field correlation functions.

Passive near-field imaging with pseudo-thermal sources.

We demonstrate experimentally that spurious effects caused by interference can be eliminated in passive near-field imaging by implementing a simple random illumination. We show that typical imaging artifacts are effectively eliminated when the radiation emitted by a pseudo-thermal source illuminates the sample and the scattered field is collected by an aperture probe over essentially all angles of incidence. This novel pseudo-thermal source can be easily implemented and significantly enhances the performance of passive near-field imaging.

Phase Transitions in Diffusion of Light.

It has been a long time belief that, with increasing the scattering strength of multiple scattering media, the transport of light gradually slows down and, eventually, comes to a halt corresponding to a localized state. Here we present experimental evidence that different stages emerge in this evolution, which cannot be described by classical diffusion with conventional scaling arguments. A microscopic model captures the relevant aspects of electromagnetic wave propagation and explains the competing mechanisms that prevent the three-dimensional wave localization.

Digital design of multimaterial photonic particles.

Scattering of light from dielectric particles whose size is on the order of an optical wavelength underlies a plethora of visual phenomena in nature and is a foundation for optical coatings and paints. Tailoring the internal nanoscale geometry of such "photonic particles" allows tuning their optical scattering characteristics beyond those afforded by their constitutive materials-however, flexible yet scalable processing approaches to produce such particles are lacking. Here, we show that a thermally induced in-fiber fluid instability permits the "digital design" of multimaterial photonic particles: the precise allocation of high refractive-index contrast materials at independently addressable radial and azimuthal coordinates within its 3D architecture.

Directional control of scattering by all-dielectric core-shell spheres.

The optical size and intrinsic material properties of scattering particles introduce inherent restrictions on their scattering patterns. We show that large size, core-shell dielectric structures with spherical symmetry provide the necessary flexibility for exciting higher-order spherical modes and, consequently, allow us to control the directivity of the scattered radiation. Significant scattering can be generated over angular domains that were formerly believed to be accessible only to dipolar scattering.

Applications of Fresnel diffraction from the edge of a transparent plate in transmission.

When a transparent plane-parallel plate is illuminated at the edge region by a quasi-monochromatic parallel beam of light, diffraction fringes appear on a plane perpendicular to the transmitted beam direction. The sharp change in the refractive index at the plate boundary imposes an abrupt change on the phase of the illuminating beam that leads to the Fresnel diffraction. The visibility of the diffraction fringes depends on the plate thickness, refractive index, light wavelength, and angle of incidence.

High precision refractometry based on Fresnel diffraction from phase plates.

When a transparent plane-parallel plate is illuminated at a boundary region by a monochromatic parallel beam of light, Fresnel diffraction occurs because of the abrupt change in phase imposed by the finite change in refractive index at the plate boundary. The visibility of the diffraction fringes varies periodically with changes in incident angle. The visibility period depends on the plate thickness and the refractive indices of the plate and the surrounding medium.