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A flexible, dual-broadband and polarization insensitive coding metasurface is proposed to manipulate electromagnetic (EM) scattering in microwave frequency band. The 1-bit coding units “0” and “1” are formed by the Pancharatnam-Berry (PB) phase based on the same-sized meta-atoms with different orientations. The layout of the coding metasurface is obtained through genetic algorithm (GA). The simulation results indicate that the proposed coding metasurface in this paper can achieve more than 10 dB radar cross section (RCS) reduction in the range of 9.26-12.87 and 14.84-19.35 GHz in the planar case, which is attributed to the reorientation of the reflected energies into different directions by optimizing the coding sequence. The diffuse scattering performance in the dual-wideband is well maintained while the coding metasurface is conformal on metallic cylinder with diverse curvature radii. Moreover, the scattering characteristics of conformal metasurfaces become better with the decrease of curvature radius under the case of the certain size of the flexible metasurface. A flexible coding metasurface prototype is prepared and measured. The experiment results coincide with the numerical simulation ones, demonstrating the outstanding capacity of RCS reduction. The proposed design has potential application value in the field of antenna and stealth of more complex objects.

Funding Information: This work was supported in part by Saab AB. The work of Mikko K. Leino was supported in part by the Walter Ahlstr?m Foundation, in part by the Jenny and Antti Wihuri Foundation, and in part by the Nokia Foundation. Publisher Copyright: © 1963-2012 IEEE. A periodically loaded, low-scattering dipole suitable for the secondary surveillance radar, particularly for identification-friend-or-foe antenna, is presented along with the methods to design such an antenna. The dipole is chopped into the pieces with length that minimizes scattering at 10 GHz, i.e., at the operation frequency of the primary antenna. In addition, optimal inductive loading is found to connect the pieces together so that the formed entity can radiate at 1 GHz, i.e., at the operation of frequency of the secondary antenna. Two meander-line designs are presented to realize the required inductances, and the proposed structures are realized on a printed circuit board. Designed prototypes are analyzed through simulations and measurements, which are in good agreement. The reduction in radar cross section at 10 GHz with the inductively loaded dipoles is at best more than 15 dB, when compared to the reference half-wave dipole. As a consequence, the radiation efficiency at 1 GHz decreases by 0.4 dB withthe inductively loaded dipoles.

In this paper, we consider the propagation of waves in an open waveguide in ℝ$^{2}$ where the index of refraction is a local perturbation of a function which is periodic along the axis of the waveguide (which we choose to be the x$_{1}$ axis) and equal to one for |x$_{2}$| > h$_{0}$ for some h$_{0}$ > 0. Motivated by the limiting absorption principle (proven in an earlier paper by the author), we formulate a radiation condition which allows the existence of propagating modes and prove uniqueness, existence, and stability of a solution under the assumption that no bound states exist. In the second part, we determine the order of decay of the radiating part of the solution in the direction of the layer and in the direction orthogonal to it. Finally, we show that it satisfies the classical Sommerfeld radiation condition and allows the definition of a far field pattern.

Near-field radar cross-section (NF-RCS) of a target depends on antennas’ radiation and can be maximized by adjusting the radiation patterns. It is justified by the power return ratio and can be computed by a comparison method. A theoretical foundation of operational mechanism for phased arrays of antennas is presented to produce conformal radiations for NF-RCS enhancement. The target’s scattering coefficients are extracted from operating the antenna array’s digital phase shifters to steer the resulting beams in this work. The scattering matrix is then analyzed by the singular value decomposition (SVD) to determine the antennas’ excitations for maximum NF-RCS with estimation stability. It results in orthogonal beams for the two-way radiations of antenna arrays to interpret the scattering mechanisms. The feasibility is validated by HFSS full-wave simulations and experimental measurement data.

In turbid water, target reflected lidar signal is easily buried in “clutter” due to scattering. We proposed an underwater laser ranging model applying an optical vortex in the receiver to separate the scattering clutter from the target reflected signal. A spiral phase plate (SPP) was placed in front of the detector to convert the target reflected Gaussian beam to an optical vortex. While the scattering clutters were not able to be converted due to the loss of spatial coherence. Therefore, the target reflected signal and scattering clutters were spatially separated by the SPP. An underwater laser detection simulation using Zemax software was carried out. The numerical simulation showed that when the SPP was placed in front of the receiver, the contrast of signal to clutter of the detection was improved by blocking the scattering clutters which had a Gaussian distribution at the center on the detection plane. The effects of beam divergence and orbital angular momentum (OAM) order to the lidar performance were also analyzed.

In this article, a hypersonic target electromagnetic (EM) scattering echo model combined with the inhomogeneous zonal medium model (IZMM) and the classical scattering center model (SCM) is proposed with a distributed satelliteborne array radar as the detection platform. A parallel physical optics (PO) method is used for multiview inverse synthetic aperture radar (ISAR) imaging of a moving hypersonic target covered with plasma sheath based on the analysis of high-resolution range profile in the S-X ultrawideband range, reconstructing 2-D EM scattering echo data (the target) and motion compensation. The results show that the surface of the inhomogeneous plasma sheath flow field is an excitation layer with random and irregular fluctuation characteristics, which increases the false scattering centroid of the 1-D range profile of the hypersonic target and can interfere with and disrupt the radar localization of the target along the radial direction. In addition, shallow scattering of EM waves occurs in the plasma sheath, and the average signal intensity of the target can gradually reduce from 0.5 x 10⁻⁵ at 60 km and 20 Ma to 0.1 x 10⁻⁵ at 30 km and 20 Ma, with a fivefold weakening of the overall scattered echo signal. In particular, the faster the hypersonic target travels at 30-km altitude, the weaker the imaged scattered echo signal becomes, with the average intensity of the imaged signal weakening by approximately threefold from 15 to 25 Ma. This study provides considerable technical support and data assurance to establish a synthetic aperture radar (SAR) automatic target recognition (ATR) database, and the findings of this study can be used as a reference for fine-structure feature analysis of hypersonic targets for feature extraction and the classification and identification of targets.

For the traditional subwavelength gratings, we can code different units to construct the coded metagratings. In this paper, we propose an innovative principle of adding coded gratings, which can be used to add or subtract two or more traditional coded metagratings sequences and obtain a new coded metagratings sequence. Based on the proposed addition principle, the coded metagratings can adjust the scattering angle flexibly. This method overcomes the limitation that traditional grating can only obtain discrete diffraction angle. Importantly, compared with traditional gratings, the coded metagrating sequences with addition operation have enhanced diffraction efficiency at the same diffraction angle. This phenomenon may be attributed to the enhanced interaction between the coding particles of the new disordered coding sequence metagratings constructed. Our proposed coded grating addition principle provides a new degree of freedom for the flexible modulation of the terahertz wavefront. At the same time, this method can be extended to optical band or microwave band, which opens a new path for electromagnetic wave modulation and beam scanning.

Optical hotspots underpin a wide variety of photonic devices ranging from sensing, nonlinear generation to photocatalysis, taking advantage of the strong light-matter interaction at the vicinity of photonic nanostructures. While plasmonic nanostructures have been widely used for strongly localized electromagnetic energy on surfaces, they suffer from high loss and consequently a low quality factor. Resonance-based dielectric structures provide an alternative solution with a larger quality factor, but there is a mismatch between the maximum values of the light confinement (quality factor) and the leakage (intensity in the near-field). Here, we propose to apply the concept of topological photonics to the formation of hotspots, producing them in both topological edge states and topological corner states. The topology secures strong light localization at the surface of the nanostructures where the underlying topological invariant shows a jump, generating a field hotspot with simultaneous increment of quality factor and light intensity. Meanwhile, it leverages a good robustness to fabrication imperfection including fluctuation in shape and misalignment. After a systematic investigation and comparison of the robustness between 1D and 2D topological structures, we conclude that the hotspots from 1D topological edge states promise a fertile playground for emerging applications that require both enhanced light intensity and high spectral resolution.

All-dielectric nanoantennas, consisting of high refractive index semiconductor material, are drawing a great deal of attention in nanophotonics. Owing to their ability to manipulate efficiently the flow of light within sub-wavelength volumes, they have become the building blocks of a wide range of new photonic metamaterials and devices. The interaction of the antenna with light is largely governed by its size, geometry, and the symmetry of the multitude of optical cavity modes it supports. Already for simple antenna shapes, unraveling the full modal spectrum using conventional far-field techniques is nearly impossible due to the spatial and spectral overlap of the modes and their symmetry mismatch with incident radiation fields. This limitation can be circumvented by using localized excitation of the antenna. Here, we report on the experimental near-field probing of optical higher order cavity modes (CMs) and whispering gallery modes (WGMs) in amorphous silicon nanoantennas with simple, but fundamental, geometrical shapes of decreasing rotational symmetry: a disk, square, and triangle. Tapping into the near-field using an aperture type scanning near-field optical microscope (SNOM) opens a window on a rich variety of optical patterns resulting from the local excitation of antenna modes of different order with even and odd parity. Numerical analysis of the antenna and SNOM probe interaction shows how the near-field patterns reveal the node positions of – and allows us to distinguish between – cavity and whispering gallery modes. As such, this study contributes to a richer and deeper characterization of the structure of light in confined nanosystems, and their impact on the structuring of the light fields they generate.

A dual-polarized lower-band (LB) antenna element is proposed in this paper. A pair of vertical arms and a pair of horizontal arms are designed with two cross -shaped feeding lines together for 45polarizations. The sleeve arm can suppress the scattering for high frequency electromagnetic wave, and have almost negligible effect on low frequency. Meanwhile, unobstructed space for placing the higher-band (HB) elements is reserved with surrounded scheme. The dual-band antenna (DBA) with four HB elements operating from 1.46~2.43 GHz and one LB element operating from 0.65~1.11 GHz is designed and fabricated. The simulated and measured results show that stable radiation performance and low mutual interference for LB and HB elements are achieved in DBA.

Electromagnetic wave scattering suppression has applications in many scenes including radio communication and electromagnetic compatibility. A large amount of research focus on absorber structures with reflection suppression at -10 dB level, while scattering suppression beyond -10dB level is rather rare. In order to study the formation of higher suppression, metamaterial with absorption and scattering composite function is presented based on coding sequence of absorptive electromagnetic genetic components. Quantized experimental measurement result of scattering suppression reaches -22.4 dB in consecutive 7.152 GHz - 16.184 GHz band (relative bandwidth 77.4%), which shows consistent trend with simulation and validates the design process. Optimization with small gene coding variation rate (4.7%) makes scattering suppression effect surpass -30 dB line in 9.45 GHz - 13.8 GHz in simulation. Besides camouflage function, this metamaterial could alter the scattering information in spatial distribution with high suppression effect, which has a good chance to serve as transmitter in local area network with good privacy.

A method to suppress cross-band scattering is presented in this letter. A two-antenna system is analyzed, which consists of a lower-band (LB) dipole and a higher-band (HB) dipole. A pair of sleeves is loaded on the arms of the LB dipole. The cross-band scattering between the HB and LB antennas close to each other usually deteriorates the pattern of the HB antenna. In the proposed antenna system, the sleeves loaded on the arms of the LB dipole are used to suppress the induced current on the LB antenna and reduce the cross-band scattering in the two-dipole system, which restores the radiation pattern of the HB antenna. A prototype of the proposed antenna system is fabricated and measured. The results show that the maximum radiation direction of the HB antenna is changed from a maximum of 24 degrees back to 0 degrees in H-plane.

This communication presents a low-profile and low scattering wideband planar phased antenna array with enhanced coupling (PAA-EC). The proposed chessboard-like PAA-EC consists of two different types of low-profile planar antenna elements that have similar radiation performance in the X-band. In addition, the two types of antenna elements have a 180° ± 37° reflection phase difference over the X-band, which guarantees the cancelation of scattering fields for low scattering purpose. On the other hand, an 8×8 reference PAA-EC and a low scattering PAA-EC are developed and fabricated to validate the radiation performance and scattering characteristics. The simulated and measured results show that the proposed low-profile planar PAA-EC operates in the 8-12 GHz band with ±45° scanning range. It also achieves at least 9-dB scattering cross section (SCS) reduction in the 8-15.2 GHz band as compared with the reference PAA-EC.

A filtering transmitarray antenna (TAA) with high-gain in-band radiations at the $X$ -band and an out-of-band low-scattering characteristic is presented in this communication. The proposed composite TAA element consists of a dual-polarized resistive sheet, a fixed bandstop frequency-selective surface (FSS) element, and an adjustable bandpass FSS element also serving as a phase shifter. The resistive element is constructed by inserting a parallel inductor–capacitor (PLC) resonant structure into the center of a lumped-resistor-loaded metallic dipole. A transparent frequency-domain window at the center operating frequency ( $f_{c}$ ) is created by the PLC resonance and is further shared by both FSS elements, hence allowing for high in-band transmission herein. At frequencies below or above $f_{c}$ , the whole composite TAA element acts as an absorber with the bandpass or bandstop FSS elements as the ground planes for the resistive sheet, respectively. The measured results show that the composite TAA can achieve gain-filtering responses with out-of-band suppression levels ≥25 dB, ~8 dB scattering cross section (SCS) reductions in 4–7 and 14–20 GHz, and the radiation gain of 25.3 dBi simultaneously. Because of these merits, the proposed design can relieve the stress on filtering circuit designs, also offering an attractive solution in stealth technology.

The complex-source (CS) method in conjunction with the spherical-multipole analysis is used to explore and demonstrate the different local phenomena associated with beam-wave scattering by acoustically hard or soft circular cones. The illumination by a beam allows a selective excitation of the scattering phenomena which include reflections, tip diffraction, and creeping beam-waves, where all of them coalesce in the vicinity of the tip. These phenomena depend on the beam’s direction and width, on whether the incident beam is converging or diverging as it hits the scatterer, and on whether the scattering point is within or beyond the beam collimation zone. A generalization of the CS method is introduced that can address converging beams. Special emphasis is given to identifying and explaining the footprint of the local diffraction phenomena. All the numerical details are provided so that the reader can readily explore the problem further. For interested readers, supplementary videos are available on IEEE DataPort that give further insight into wave physics and clarify the direction of wave propagation.

The two-photon fluorescence imaging depth has been significantly improved in recent years by compensating for tissue scattering with wavefront correction. However, in most approaches the wavefront corrections are valid only over a small sample region on the order of 1 to 10 µm. In samples where most scattering structures are confined to a single plane, sample conjugate correction geometries can increase the observable field to a few tens of µm. Here, we apply a recently introduced fast converging scheme for sensor-less scattering correction termed “Dynamic Adaptive Scattering compensation Holography” (DASH) in a sample conjugate configuration with a high pixel count nematic liquid crystal spatial light modulator (LC-SLM). Using a large SLM allows us to simultaneously correct for scattering at multiple field points, which can be distributed over the entire field of view provided by the objective lens. Despite the comparably slow refresh time of LC-SLMs, we achieve correction times on the order of 10 s per field point, which we show is sufficiently fast to counteract scattering at multiple sites in living mouse hippocampal tissue slices.

The coherence properties of the beam provided at the CoSAXS beamline at the MAX IV Laboratory are determined experimentally using multi-mode ptychography. The coherent fraction of the beam is then used for a proof-of-concept XPCS measurement, illustrating the beamline’s capabilities., The CoSAXS beamline at the MAX IV Laboratory is a modern multi-purpose (coherent) small-angle X-ray scattering (CoSAXS) instrument, designed to provide intense and optionally coherent illumination at the sample position, enabling coherent imaging and speckle contrast techniques. X-ray tracing simulations used to design the beamline optics have predicted a total photon flux of 1012–1013 photons s−1 and a degree of coherence of up to 10% at 7.1 keV. The normalized degree of coherence and the coherent flux of this instrument were experimentally determined using the separability of a ptychographic reconstruction into multiple mutually incoherent modes and thus the Coherence in the name CoSAXS was verified. How the beamline can be used both for coherent imaging and XPCS measurements, which both heavily rely on the degree of coherence of the beam, was demonstrated. These results are the first experimental quantification of coherence properties in a SAXS instrument at a fourth-generation synchrotron light source.

Plasmonic gold nanorods (GNRs) are finding increasing use in biomedicine due to their unique electromagnetic properties, optical contrast enhancement and biocompatibility; they also show promise as polarization contrast agents. However, quantification of their polarization-enhancing properties within heterogeneous turbid media remains challenging. We report on polarization response in controlled tissue phantoms consisting of dielectric microsphere scatterers with varying admixtures of GRNs. Experimental Mueller matrix measurements and polarization sensitive Monte-Carlo simulations show excellent agreement. Despite the GNRs’ 3D random orientation and distribution in the strong multiply scattering background, significant linear diattenuation and retardance were observed. These exclusive measurable characteristics of GNRs suggest their potential uses as contrast enhancers for polarimetric assessment of turbid biological tissue.

In this article, we propose a software–hardware system to improve the quality of image recovery in millimeter-wave (MMW) imaging systems, which aims to benefit from copolarization and cross-polarization scatterings from the target. The proposed dual-polarized antenna array structures consist of two orthogonal subarrays with the same phase center, where each subarray is comprised of $2\times 1$ or $4\times 1$ rectangular edge fed patches and the optimized ground defects. These compact structures, which support radiation of two orthogonal linear polarizations, are designed on a single-layer board using crossover technique. The dual-polarized scattering from the target is captured by the orthogonal subarrays. Furthermore, we introduce a method to combine data obtained from measured dual (co- and cross-) polarized fields to improve the recovery of edge information and increase image quality. The proposed single-layer designs have been fabricated and measured, which exhibits high port isolation and high polarization purity. The cross-polarization level is at least 22 and 25 dB lower than the copolarization pattern for $2\times 1$ and $4\times 1$ arrays, respectively. The measured 10 dB impedance bandwidth of the $2 \times 1$ and $4\times 1$ subarrays ranges from 27 to 29.3 GHz and from 27 to 29.5 GHz, respectively. Moreover, the radiation gains of the $2 \times 1$ and $4\times 1$ subarrays are 9.7 and 12 dBi, respectively. The simulated and measured imaging results show that the cross-polarized data preserve the edge information. Moreover, by using the proposed data combination technique, the quality of the recovered image is improved.

Soft protons are a potential threat for X-ray missions using grazing incidence optics, as once focused onto the detectors they can contribute to increase the background and possibly induce radiation damage as well. The assessment of these undesired effects is especially relevant for the future ESA X-ray mission Athena, due to its large collecting area. To prevent degradation of the instrumental performance, which ultimately could compromise some of the scientific goals of the mission, the adoption of ad-hoc magnetic diverters is envisaged. Dedicated laboratory measurements are fundamental to understand the mechanisms of proton forward scattering, validate the application of the existing physical models to the Athena case and support the design of the diverters. In this paper we report on scattering efficiency measurements of soft protons impinging at grazing incidence onto a Silicon Pore Optics sample, conducted in the framework of the EXACRAD project. Measurements were taken at two different energies, ~470 keV and ~170 keV, and at four different scattering angles between 0.6 deg and 1.2 deg. The results are generally consistent with previous measurements conducted on eROSITA mirror samples, and as expected the peak of the scattering efficiency is found around the angle of specular reflection., 16 pages, 11 figures; accepted for publication on Experimental Astronomy

International audience; Evanescent-wave scattering is a topic in classical electrodynamics and in the study of colloidal particles near a boundary. However, how such near-surface scattering at subcellular refractive-index heterogeneities degrades the excitation confinement in biological total internal reflection fluorescence microscopy has not been well studied. An elegant theoretical work by Axelrod and Axelrod now addresses this very relevant question and reveals that-even when scattered-evanescent light preserves some of its surprising optical properties.

The modification of a conventional plasma window antenna (PWA) into a novel endfire plasma array antenna (E-PAA) and the comparison of their performances are first made. It will be shown that the E-PAA provides better performance than the PWA does. Then, the gain improvement and more importantly the radar cross section (RCS) reductions for stealth properties of the E-PAA are described. A type of feeding and generating system of plasma antenna is given. Simulated and measured results at 300 MHz are discussed, indicating the potential applications of the E-PAA in high-level integrating of radio transceivers onboard for wireless communications.

The hyperbolic phonon polaritons supported in hexagonal boron nitride (hBN) with long scattering lifetimes are advantageous for applications such as super-resolution imaging via hyperlensing. Yet, hyperlens imaging is challenging for distinguishing individual and closely spaced objects and for correlating the complicated hyperlens fields with the structure of an unknown object underneath. Here, we make significant strides to overcome each of these challenges. First, we demonstrate that monoisotopic h11BN provides significant improvements in spatial resolution, experimentally resolving structures as small as 44 nm and those with sub 25 nm spacings at 6.76 μm free-space wavelength. We also present an image reconstruction algorithm that provides a structurally accurate, visual representation of the embedded objects from the complex hyperlens field. Further, we offer additional insights into optimizing hyperlens performance on the basis of material properties, with an eye toward realizing far-field imaging modalities. Thus, our results significantly advance label-free, high-resolution, spectrally selective hyperlens imaging and image reconstruction methodologies.

Surface plasmon polariton (SPP) waves are the most extensively studied waves among various types of surface waves because they are easy to excite and have been used in many optical applications particularly for plasmonic communication, sensing, and harvesting solar energy. In all these applications, especially on-chip plasmonic communication, scattering can be an important issue to deal with. Therefore, this paper aimed to theoretically inspect the scattering pattern of SPP waves from a perfect electric conductor (PEC) cylindrical scatterer. The cylindrical wave approach is used to solve the scattering problem by a cylindrical object placed below a metallic layer. The scattering is investigated thoroughly by changing the size of the scatterer and its distance from the interface along which the SPP wave is excited. As the size of the scatterer increases, the scattering increases significantly. On the other hand, when the distance of the scatterer from the interface is increased, the scattered field becomes small. Two-dimensional field maps are produced for the incident angle at which SPP is excited. Numerical results are also presented for other incident angles to make a comparison. Furthermore, the forward and backward far-fields are significantly enhanced if the SPP wave is scattered in comparison with when the SPP wave is not present.

Asymptotic solutions based on the uniform geometrical theory of diffraction (UTD) are well developed and efficient for analyzing radiation, mutual coupling, and scattering associated with electrically large conducting convex surfaces. Relevant UTD solutions are available mostly for infinitesimal sources on or far away from the surface. Hence, UTD solutions have been extensively used to analyze radiation from conformal antennas and antenna arrays on an electrically large convex surface. In this letter, it is proposed to predict far and near field radiations from a monopole antenna array on an electrically large conducting convex surface as a nonconformal array. A UTD solution that allows sources to be on or slightly off the surface is employed after identifying ray paths. UTD results are validated with those of the multilevel fast multipole method.

In this chapter, neutron experimental techniques are described. The chapter covers the basics of neutron scattering, neutron source characteristics, diffraction techniques, inelastic neutron scattering, instruments for semi-macroscopic structure analysis, detectors, optics, choppers, and some concepts for instrument design. Techniques for both steady and pulsed sources are described, with more emphasis on the latter in view of the recent worldwide trend toward pulsed sources, generally pulsed spallation sources. The source character, even within the class of pulsed sources, has a significant influence on instrument design. Inelasticity effects in the total scattering technique are clearly specified in the chapter. Some details of chopper instruments, including resolution effects, are described, since this class of instruments has recently received considerable innovative development and use over a wide range of science. Recent developments in scintillation detectors are discussed as an alternative technology to more conventional 3He detectors. Optical components are becoming more and more important not only for neutron transport but also for background reduction. Neutron spin-echo techniques are presented as an example of the exploitation of polarized neutrons.

Validation of remote sensing retrievals of aerosol microphysical and optical properties requires in situ measurements of the same properties. We present here an improved imaging nephelometer for measuring the directionality and polarization of light (i.e., polarimetry) scattered at two wavelengths (405 and 660 nm) with high temporal resolution. The instrument was designed for airborne deployment and is capable of ground-based measurements as well. The laser imaging nephelometer (LiNeph) uses two orthogonal detectors with wide-angle lenses and linearly polarized light sources to measure both the phase function, P11(θ), and degree of linear polarization, -P12/P11(θ). In this work, we will describe the instrument function and calibration, as well as data acquisition and reduction. The instrument was first deployed aboard the NASA DC-8 during the 2019 FIREX-AQ campaign. Here, we present field measurements of smoke plumes that show that the LiNeph has sufficient resolution for 0.24 Hz polarimetric measurements at two wavelengths, 405 and 660 nm, at integrated scattering coefficients ranging from 50–8000 Mm−1.

Light diffraction at an aperture is a basic problem that has generated a tremendous amount of interest in optics. Some of the most significant diffraction results are the Fresnel-Kirchhoff and Rayleigh-Sommerfeld formulas. These theories are based on solving the wave equation using Green’s theorem and result in slightly different expressions depending on the particular boundary conditions employed. In this paper, we show that the diffraction by a thin screen, which includes apertures, gratings, transparencies etc, can be treated more generally as a particular case of scattering. Furthermore, applying the first order Born approximation to 2D objects, we obtain a general diffraction formula, without angular approximations. Finally, our result, which contains no obliquity factor, is consistent with the 3D theory of scattering. We discuss several common approximations and place our results in the context of existing theories.

We consider accurate and iteratively efficient solutions of electromagnetic problems involving homogenized near-zero-index (NZI) bodies using surface-integral-equation formulations in the frequency domain. NZI structures can be practically useful in a plethora of optical applications, as they possess near-zero permittivity and/or permeability values that cannot be found in nature. Hence, numerical simulations are of the utmost importance for rigorous design and analysis of NZI structures. Unfortunately, small values of electromagnetic parameters bring computational challenges in numerical solutions of homogeneous models. Conventional formulations available in the literature encounter stability issues that make them inaccurate and/or inefficient as permittivity and/or permeability approach zero. We propose a novel formulation that involves a well-balanced combination of operators and that can provide both accurate and efficient solutions for all NZI cases. Numerical results are presented to demonstrate the superior properties of the developed formulation in comparison to the conventional ones.

We show that by modifying the chemical interface of silver nanoparticles (AgNPs) with halide ions, it is possible to tune the total decay rate of adsorbed excited molecules and the plasmon damping rate. Through single-molecule surface-enhanced Raman scattering and surface-enhanced fluorescence enhancement factors of crystal violet (CV) and rhodamine 6G (R6G), we show that I–-modified AgNPs (AgNPs@I) and Br–-modified AgNPs (AgNPs@Br) lead to an increase in the total decay rate of excited CV and R6G by a factor between ∼1.6–2.6, compared to Cl–-modified AgNPs (AgNPs@Cl). In addition, we found that the chemical interface damping, which characterizes the plasmon resonance decay into surface states, is stronger on AgNPs@I and AgNPs@Br when compared to AgNPs@Cl. These results point toward the formation of metal–halide surface complexes. These new interfacial states can accept electrons from both excited molecular orbitals and surface plasmon excitations, completely altering the electronic dynamics and reactivity of plasmonic interfaces.

In relation to the computation of electromagnetic scattering in layered media by the Gabor-frame-based spatial spectral Maxwell solver, we present two methods to compute the Gabor coefficients of the transverse cross section of three-dimensional scattering objects with high accuracy and efficiency. The first method employs the analytically obtained two-dimensional Fourier transform of the cross section of a scattering object, which we describe by two-dimensional characteristic functions, in combination with the traditional discrete Gabor transform method for computing the Gabor coefficients. The second method concerns the expansion of the so-called dual window function to compute the Gabor coefficients by employing the divergence theorem. Both methods utilize (semi)-analytical approaches to overcome the heavy oversampling requirement of the traditional discrete Gabor transform method in the case of discontinuous functions. Numerical results show significant improvement in terms of accuracy and computation time for these two methods against the traditional discrete Gabor transform method.

We introduce the fdRLoS fading model as a natural generalization of the double-Rayleigh with line-of-sight fading model, on which the constant-amplitude line-of-sight component is now allowed to randomly fluctuate. We discuss the key benefits of the fdRLoS fading model here formulated over the state of the art, and provide an analytical characterization of its chief probability functions. We analyze the effect of the fading parameters that define the model, and discuss their impact on the performance of wireless communication systems., Comment: Article with 4 pages and 4 figures containing original research results for wireless fading modelling. Submmited to Transactions on Vehicular Technologies (TVT) - Correspondence - on July the 16th, 2021

This work was supported by the STFC Central Laser Facility, the STFC Centre for Fundamental physics and by EPSRC through Grant EP/G04239X/1. We acknowledge PRACE for providing access to the resource SuperMUC based in Germany at the Leibniz Research Center. LOS acknowledges the support of the European Research Council (ERC-2015-AdG Grant No. 695088). Brillouin amplification of laser pulses in plasma has been shown to be a promising approach to produce picosecond pulses of petawatt power. A key challenge is preservation of the quality of the amplified pulse, which requires control of parasitic instabilities that accompany the amplification process. At high plasma densities ( >cr /4), ponderomotive filamentation has been identified as the biggest threat to the integrity of the amplifying pulse. It has therefore been proposed to perform Brillouin scattering at densities below ncr/4 to reduce the influence of filamentation. However, parasitic Raman scattering can become a problem at such densities, contrary to densities above ncr/4 where it is forbidden. In this paper, we investigate the influence of parasitic Raman scattering on Brillouin amplification at densities below ncr/4 . We expose the specific problems posed by both Raman backward and forward scattering, and how both types of scattering can be mitigated, leading to an increased performance of the Brillouin amplification process. Publisher PDF

Soni, S., et al. (LIGO Scientific Collaboration), Noise due to scattered light has been a frequent disturbance in the advanced LIGO gravitational wave detectors, hindering the detection of gravitational waves. The non stationary scatter noise caused by low frequency motion can be recognized as arches in the time-frequency plane of the gravitational wave channel. In this paper, we characterize the scattering noise for LIGO and Virgo's third observing run O3 from April, 2019 to March, 2020. We find at least two different populations of scattering noise and we investigate the multiple origins of one of them as well as its mitigation. We find that relative motion between two specific surfaces is strongly correlated with the presence of scattered light and we implement a technique to reduce this motion. We also present an algorithm using a witness channel to identify the times this noise can be present in the detector., LIGO was constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the National Science Foundation and operates under Cooperative Agreement No. PHY-1764464. Advanced LIGO was built under Grant No. PHY-0823459. We acknowledge support from the NSF grant PHY-1806656, PHY-1505779, and PHY-1912604. We also acknowledge the discussions with the members of Detector Characterization Group of the LIGO Scientific Collaboration.

[EN] In this work, we show that scattered acoustic vortices generated by metasurfaces with chiral symmetry present broadband unusual properties in the far-field. These metasurfaces are designed to encode the holographic field of an acoustical vortex, resulting in structures with spiral geometry. In the near field, phase dislocations with tuned topological charge emerge when the scattered waves interference destructively along the axis of the spiral metasurface. In the far field, metasurfaces based on holographic vortices inhibit specular reflections because all scattered waves also interfere destructively in the normal direction. In addition, the scattering function in the far field is unusually uniform because the reflected waves diverge spherically from the holographic focal point. In this way, by triggering vorticity, energy can be evenly reflected in all directions except to the normal. As a consequence, the designed metasurface presents a mean correlation-scattering coefficient of 0.99 (0.98 in experiments) and a mean normalized diffusion coefficient of 0.73 (0.76 in experiments) over a 4 octave frequency band. The singular features of the resulting metasurfaces with chiral geometry allow the simultaneous generation of broadband, diffuse and non-specular scattering. These three exceptional features make spiral metasurfaces extraordinary candidates for controlling acoustic scattering and generating diffuse sound reflections in several applications and branches of wave physics as underwater acoustics, biomedical ultrasound, particle manipulation devices or room acoustics., We acknowledge financial support from the Spanish Ministry of Science, Innovation and Universities through Grant "Juan de la Cierva-Incorporacion" (IJC2018-037897-I) and PID2019-111436RB-C22, and by the Agencia Valenciana de la Innovacio through grants INNVAL10/19/016. This article is based upon work from COST Action DENORMS CA15125, supported by COST (European Cooperation in Science and Technology). JPG and VRG gratefully acknowledge the ANR-RGC METARoom (ANR-18-CE08-0021) project and the project HYPERMETA funded under the program Etoiles Montantes of the Region Pays de la Loire.

Enhanced-resolution imaging in complex scattering media is revisited from a parameter estimation perspective. A suitably defined Fisher information is shown to offer useful insights into the limiting precision of parameter estimation in a scattering environment and, hence, into the limiting spatial resolution that can be achieved in imaging-through-scattering settings. The Fisher information that defines this resolution limit via the Cramér–Rao lower bound is shown to scale with the number of adaptively controlled space–time modes of the probe field, suggesting a physically intuitive generalization of the Abbe limit to the spatial resolution attainable for complex scattering systems. In a conventional, direct-imaging microscopy setting, this bound is shown to converge to the canonical Abbe limit.

Rainbow refractometry has been used in the past to measure size and refractive index of spherical particles, typically droplets in a spray. In the present study, conventional optical configurations for point measurements or line measurements have been extended to allow also the particle position in a plane to be determined, and hence, the designation planar rainbow refractometry. However, this extension introduces challenges in accurately calibrating the 2D scattering angles with the image coordinates. This challenge has been met using a novel calibration method, employing a monodispersed droplet stream traversed through the measurement plane. Experiments confirm achievable horizontal and vertical position accuracies of 0.42 mm and 0.36 mm, respectively, and a refractive index uncertainty of 2 × 10 − 4 .

Resonant electromagnetic scattering has been optimized for angularly inhomogeneous nanotubes characterized by different surface admittances along the two complementary arcs. The optimal designs are substantially more efficient compared to their best homogeneous counterparts and the spatial distribution of the scattering power reveals the nature of the sustained resonances. In this sense, the reported scattering scores constitute limits for the response of that simple class of structures and can be employed as optimized components in a wide spectrum of photonic devices from wave transformers and field sensors to electromagnetic filters and optical lenses.

Bi-directional reflection distribution function (BRDF) is a common method to study the laser scattering characteristics of targets, and it is an important parameter for the theoretical demonstration of laser active detection, target recognition and classification. Scholars at home and abroad have proposed many mature BRDF models to describe the scattering characteristics of different targets. However, almost all of these models do not take into account the effect of incident wavelength on scattering characteristics. In addition, limited by the frequency modulation range of the laser, the existing BRDF measurement devices cannot obtain the BRDF data of the target at any wavelength, which restricts the application of the existing BRDF model. In view of this limitation, a method is proposed to calculate the unknown wavelength BRDF data using the BRDF measurement data of known wavelengths. Firstly, based on the Kirchhoff approximation theory, the spatial distribution of the scattered light field of the metal aluminum target at any wavelength was simulated and analyzed. Secondly, the error of the theoretical simulation model was analyzed through the experimental data. Finally, the BRDF data at any wavelength were calculated using the simulation data and the experimental data with known wavelengths. The final results showed that at the 1064nm wavelength, the RMSE value of the calculated data obtained by this method is 0.3553, which is 0.2233 smaller than the RMSE value of the simulation data.This method is effective in calculating the BRDF of metal aluminum targets at different wavelengths.

Aiming at the problem that the background noise mixed in the target echo will affect the calculation of the target polarization degree when the traditional polarization detection system obtains the target polarization degree, based on the polarization Gm-APD detection model, a set of target echo polarization correction method is proposed. The target is imaged in a xenon lamp environment, the influence of target attitude and polarization angle on detection is explored, and the polarization imaging results are analyzed. The results show that the polarization system has a significant effect on metal materials with low surface roughness. When circularly polarized light is incident, the echo trigger probability of the metal material reaches a peak at the polarization angle of 135°. The greater the incident angle, the greater the echo depolarization and the lower the trigger probability. By inverting the distribution of echo photons, the number of background noise photons in the echo and the number of target echo photons can be obtained respectively, and a more accurate correction of the polarization degree of the target echo can be obtained. For metal materials, when the target attitude angle is 30°, the target polarization before and after correction are 0.47 and 0.57 respectively, and the target echo polarization after correction is 7% higher than that without correction. This research work provides experimental support for the effective detection and target detection of GM-APD lidar in the daytime.

Electrons in indirect semiconductors can optically transit between the valance and conduction band edges only when the momentum conservation is satisfied with help of a third quasi-particle, such as a phonon. In this report, we theoretically demonstrate that indirect interband transition of graphene electrons can be optically enabled only by light with highly enhanced transversal modes, which can be generated by scattering of point dipole radiation with periodic metal slits fabricated in a natural hyperbolic material. The light-matter interaction for graphene electrons is reformulated by using indirect transition matrix elements, and interband polarizations of graphene are obtained by solving quantum kinetic equations of motion in the semi-classical regime. The interband optical current density of graphene as a function of the polarization angle of the incident field shows clear hexagonal response to the high transversal modes of light, which results from the low dependence on dephasing rate and dominance of the indirect polarizations over the direct interband contributions.

Color imaging with scattered light is crucial to many practical applications and becomes one of the focuses in optical imaging fields. More physics theories have been introduced in the deep learning (DL) approach for the optical tasks and improve the imaging capability a lot. Here, an efficient color imaging method is proposed in reconstructing complex objects hidden behind unknown opaque scattering layers, which can obtain high reconstruction fidelity in spatial structure and accurate restoration in color information by training with only one diffuser. More information is excavated by utilizing the scattering redundancy and promotes the physics-aware DL approach to reconstruct the color objects hidden behind unknown opaque scattering layers with robust generalization capability by an efficient means. This approach gives impetus to color imaging through dynamic scattering media and provides an enlightening reference for solving complex inverse problems based on physics-aware DL methods.

In this work we propose and analyze techniques of in-plane directionality control of strongly localized resonant modes of light in random arrays of dielectric scatterers. Based on reported diameters and areal densities of epitaxially grown self-organized nanowires, two-dimensional (2D) arrays of dielectric scatterers have been analyzed where randomness is gradually increased along a preferred direction of directionality enhancement. In view of the multiple-scattering mediated wave dynamics and directionality enhancement of light in such arrays, a more conveniently realizable, practical structure is proposed where a 2D periodic array is juxtaposed with a uniform, random scattering medium. Far- and near-field emission characteristics of such arrays show that in spite of the utter lack of periodicity in the disordered regime of the structure, directionality of the high-Q resonant modes is modified such that on average more than 70% of the output power is emitted along the pre-defined direction of preference. Such directionality enhancement and strong localization are nonexistent when the 2D periodic array is replaced with a one-dimensional Bragg reflector, thereby confirming the governing role of in-plane multiple scattering in the process. The techniques presented herein offer novel means of realizing not only directionality tunable edge-emitting random lasers but also numerous other disordered media based photonic structures and systems with higher degrees of control and tunability.

Scattering and correlation properties of a two-photon (TP) pulse are studied in a four-terminal waveguide system, i.e., two one-dimensional waveguides connected by a Jaynes-Cummings emitter (JCE). The wave function approach is utilized to exactly calculate the real-time dynamic evolution of the TP transport. When the width of the incident TP Gaussian pulse is much larger than the photon wavelength, the TP transmission spectra approach that of the corresponding single photon cases and are almost independent of the pulse width. On the contrary, as the pulse width is comparable to the photon wavelength, the TP transmission and correlation both show strong dependence on the pulse width. The resonant scattering due to the JCE and the photon interference together determine the TP correlation. When the distance between the TPs is small, the TP correlations between any two terminals for the scattered TP pulse are much different from those for the incident TP pulse and therefore, such a four-terminal waveguide system provides a way to control the TP correlation.

Double slits with molecular states Despite decades of research, the role of quantum mechanical effects in molecular scattering has not yet been fully investigated and can still demonstrate fascinating results, even for simple triatomic systems. Zhou et al . show that the entangled bond axis orientations in the biaxial state of a deuterium molecule can act as the two slits of a double-slit interferometer for rotationally inelastic collision with a helium atom, giving rise to quantum interference between two indistinguishable pathways (see the Perspective by Wang and Yang). The present work presents an elegant example of quantum interference in molecular scattering that is conceptually similar to the famous Young’s optical double-slit experiment. The proposed molecular interferometer could be used to coherently control the phases in various molecular processes in future experiments. —YS

The attenuation of backscattered light through human tissue makes it difficult to measure the interferometric signal with high accuracy. We present a new method that combines the originally developed Time Domain-OCT (TD-OCT) technique with Ghost Imaging (GI) technique to detect targets at a certain depth in the scattering medium. Our method's first result shows that sample images can be reconstructed through a homogeneous mixture of 0.5% milk solution (1 cm thickness) scattering medium. Theoretical calculations show that it is possible to reconstruct images in higher milk solutions (about 20%) with optical properties close to human tissues.

The polarization parametric indirect microscopic imaging (PIMI) method, which employs a polarization-modulated incidence illumination and fitting the far-field variation of polarization states of scattered photons, is capable of direct identification of subdiffraction-scale structures and substances, such as virus particles. However, in the present strategy, the optical elements that collect the scattered photons are nearly fixed above the sample, making the collected information relatively limited, as the side-scattering photons are not fully utilized. To address this problem, we propose a multiperspective PIMI imaging method to maximize the collection of scattering photons from different spatial directions, which can obtain more information of optical anisotropy among particles. As a proof-of-concept study, virus detection using such a method is performed theoretically and experimentally. Results reveal that the virus particles can be detected and determined more distinctly thanks to the set of PIMI images from different spatial angles, showing notable superiority to the previous scheme, where only a plane PIMI image is derived from a fixed spatial direction. With the capability of acquiring more characteristics of the samples, the proposed multiperspective PIMI method can be applied in many fields, such as morphological characterization and biosensing.

Spatiotemporal information about light pulse propagation obtained with femtosecond temporal resolution plays an important role in understanding transient phenomena and light–matter interactions. Although ultrafast optical imaging techniques have been developed, it is still difficult to capture light pulse propagation spatiotemporally. Furthermore, imaging through a three-dimensional (3-D) scattering medium is a longstanding challenge due to the optical scattering caused by the interaction between light pulse and a 3-D scattering medium. Here, we propose a technique for ultrafast optical imaging of light pulses propagating inside a 3D scattering medium. We record an image of the light pulse propagation using the ultrashort light pulse even when the interaction between light pulse and a 3-D scattering medium causes the optical scattering. We demonstrated our proposed technique by recording converging, refracted, and diffracted propagating light for 59 ps with femtosecond temporal resolution.