Wigner distribution and entropy of partially coherent light generated by perfect optical vortices.

We developed analytical expressions for the Wigner distribution function of partially coherent fields generated by the scattering of beams with a particular phase structure, namely perfect optical vortex beams. In addition, we provide the modal decomposition of the field correlations and evaluate the evolution of Shannon entropy associated with the partially coherent field.

Self-referenced single-shot low-power Stokes polarimetry.

We demonstrate a Stokes polarimeter that not only preserves the power of the light to be analyzed but also requires only a single measurement. The novel design relies on the distinctive characteristics of a corner-cube retroreflector. It is simple and robust, and it circumvents the need for a local oscillator or a controllable reference beam.

Propagation of asymmetric optical vortex beams through turbulence and evolution of their OAM spectra.

In the realm of wave propagation through turbulent media, the spectrum of the orbital angular momentum of optical vortex beams is known to undergo symmetric broadening. However, the evolution of beams that are initially azimuthally asymmetric represents a distinct phenomenon. In this work, we have developed an analytical model describing the propagation of asymmetric OAM beams through the so-called Kolmogorov turbulence. Our results describe how the perturbation strength and the initial beam properties lead to a nonsymmetric spectrum of OAM modes. These findings lay the groundwork for further use of asymmetric fields that propagate in inhomogeneous media and their applications such as communications and sensing.

First-order statistics of intensity and phase in Laguerre-Gauss speckles.

Laguerre-Gaussian (LG) beams are characterized by an azimuthal index or topological charge (m), associated with the orbital angular momentum, and by a radial index (p), which represents the number of the rings in the intensity distribution. We present a detailed, systematic study of the first-order phase statistics of the speckle fields created when LG beams of different order interact with random phase screens with different optical roughness. The phase properties of the LG speckle fields are studied in both the Fresnel and the Fraunhofer regimes using the equiprobability density ellipse formalism such that analytical expressions can be derived for the phase statistics.

Passive high-frequency microrheology of blood.

Indicative of various pathologies, blood properties are under intense scrutiny. The hemorheological characteristics are traditionally gauged by bulk, low-frequency indicators that average out critical information about the complex, multi-scale, and multi-component structure. In particular, one cannot discriminate between the erythrocytes contribution to global rheology and the impact of plasma. Nevertheless, in their fast stochastic movement, before they encounter each other, the erythrocytes probe the subtle viscoelasticity of their protein-rich environment. Thus, if these short time scales can be resolved experimentally, the plasma properties could be determined without having to separate the blood components; the blood is practically testing itself. This microrheological description of blood plasma provides a direct link between the composition of whole blood and its coagulability status. We present a parametric model for the viscoelasticity of plasma, which is probed by the erythrocytes over frequency ranges of kilohertz in a picoliter-sized volume. The model is validated both in vitro, using artificial hemo-systems where the composition is controlled, as well as on whole blood where continuous measurements provide real-time information. We also discuss the possibility of using this passive microrheology as an in vivo assay for clinically relevant situations where the blood clotting condition must be observed and managed continuously for diagnosis or during therapeutic procedures at different stages of hemostatic and thrombotic processes.

3D intensity correlations in random fields created by vortex structured beams.

We develop an analytical model for the 3D spatial coherence function of speckle fields generated by scattering of vortex and perfect optical vortex beams. The model is general and describes the spatial coherence along both the transversal and the longitudinal directions. We found that, on propagation, the 3D spatial coherence evolves differently for the different types of initially structured beams, which may affect their use in a variety of sensing applications.

Single-shot omnidirectional Stokes polarimetry.

Many active sensing applications benefit from measuring, as fast as possible, the polarization state of target reflections. Traditional polarimetry, however, relies on (1) the assumption of field transversality and (2) a given direction of wave propagation. When this is not known, one must regard the field as being three-dimensional, which inherently complicates the polarimetry due to experimental constraints imposed by the planar geometry of detector arrays. We demonstrate a single-shot, Stokes polarimetry approach that alleviates these limitations. The approach is based on the spatial Fourier analysis of the interference between the unknown wave and controlled reference fields.

Discriminating randomly polarized fields.

We introduce the scalar average similarity of an ensemble of randomly polarized states. This global measure is based on the complex degree of mutual polarization between any pair of vector fields in the ensemble. We show that, in the case of fully correlated and globally unpolarized fields, the variation of this parameter is bounded, and its value can effectively discriminate between different configurations of pure states.

Nonstationary Intensity Statistics in Diffusive Waves.

It is a long-standing belief that, in the diffusion regime, the intensity statistics is always stationary and its probability distribution follows a negative exponential decay. Here, we demonstrate that, in fact, in reflection from strong disordered media, the intensity statistics changes through different stages of the diffusion. We present a statistical model that describes this nonstationary property and takes into account the evolving balance between recurrent scattering and near field coupling. The predictions are further verified by systematic experiments in the optical regime. This statistical nonstationary is akin to the nonequilibrium but steady-state diffusion of particulate systems.

Vector wave simulation of active imaging through random media.

When a target is embedded in random media, the quality of optical imaging can be improved by actively controlling the illumination and exploiting vector wave properties. A rigorous description, however, requires expensive computational resources to fully account for the electromagnetic boundary conditions. Here, we introduce a statistically equivalent scaling model that allows for reducing the complexity of the problem. The new scheme describes the entanglement between the local wave vector and the polarization state in random media and also accounts for cumulative properties such as geometric phase. The approach is validated for different scenarios where the coherent background noise alters substantially the performance of active imaging.

First-order statistics of the phase in optical vortex speckles.

We present the theoretical analysis of first-order statistics of the phase in a far-field speckle field, which originates from an optical vortex passing through a random phase screen. By using the concept of the equiprobability density ellipse, we show that the standard deviation of the phase in a speckle field varies non-monotonically in the radial direction and, more interestingly, it exhibits a minimum at a certain radial position determined by the topological charge. In the limit of zero topological charge, the phase statistics naturally converges to the expectation corresponding to the incident Gaussian beam.

Polarization-encoded field measurement in subwavelength scattering.

We demonstrate that polarization encoding provides a convenient way to realize a robust common-path interferometer for measuring both the phase and the amplitude of scattered optical fields. Moreover, for a given detector array, the design allows maximizing the interferometric visibility and, therefore, permits reaching the sensitivity limit for the field measurement. The approach is of particular interest for inefficient scattering scenarios such as subwavelength scattering.

Spatial intensity correlations of a vortex beam and a perfect optical vortex beam.

We present a model based on the Fresnel diffraction scheme for the spatial coherence function of random fields created by scattering optical vortex and perfect vortex beams. By using the spatial coherence function we showed analytically, numerically, and experimentally the dependence and independence of the speckle size of an optical vortex and perfect optical vortex (POV) with a topological charge, respectively. We also showed in both cases the linear dependence of speckle size on the distance of propagation. Furthermore, we describe a regime in which the spatial coherence function is nonevolving for the optical vortex beam and the POV beam with the propagation distance.

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. Exploiting this unique capability in all-dielectric systems, we tune the scattering cross-section of equisized particles via radial structuring and induce polarization-sensitive scattering from spherical particles with broken internal rotational symmetry. The scalability of this fabrication strategy promises a generation of optical coatings in which sophisticated functionality is realized at the level of the individual particles.

Non-evolving spatial coherence function.

We present a general model for the spatial coherence function of random fields created by scattering elliptical, perfect vortex beams. Remarkably, as opposed to the free-space propagation of typical random fields, there are regimes where the spatial coherence function does not evolve. We demonstrate analytically, numerically, and experimentally that both the size and the shape of spatial correlations can be precisely controlled in a manner that is independent of propagation distance.

On the inverse problem of source reconstruction from coherence measurements.

We consider an inverse source problem for partially coherent light propagating in the Fresnel regime. The data are the coherence of the field measured away from the source. The reconstruction is based on a minimum residue formulation, which uses the authors' recent closed-form approximation formula for the coherence of the propagated field. The developed algorithms require a small data sample for convergence and yield stable inversion by exploiting information in the coherence as opposed to intensity-only measurements. Examples with both simulated and experimental data demonstrate the ability of the proposed approach to simultaneously recover complex sources in different planes transverse to the direction of propagation.

Non-conservative optical forces.

Undoubtedly, laser tweezers are the most recognized application of optically induced mechanical action. Their operation is usually described in terms of conservative forces originating from intensity gradients. However, the fundamental optical action on matter is non-conservative. We will review different manifestations of non-conservative optical forces (NCF) and discuss their dependence on the specific spatial properties of optical fields that generate them. New developments relevant to the NCF such as tractor beams and transversal forces are also discussed.

Single-shot coherent noise suppression by spatial interferometric heterodyning.

Coherent noise affects the information content in active imaging systems. Here we show that noise reduction can be accomplished using the intrinsic coherence properties of the electromagnetic fields. We demonstrate numerically and experimentally that a single-shot measurement using interferometric spatial heterodyning detection in conjuncture with computational image processing, permits suppressing coherent noise in conditions of low signal-to-noise ratios, through spectral upshifting of coherent information.

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.

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. In this case, a generalized Babinet's principle can be derived that applies to the spatial coherence functions. We present both the derivation and the experimental demonstration of this generalized Babinet theorem.