Characterizing extended changes in multiple scattering media using coda wave decorrelation: numerical simulations

In multiple scattering media, the coda wave decorrelation relates linearly to the scattering cross-section of structural change when the change is small compared to the wavelength. In practical applications, we assume that the total decorrelation induced by changes in the medium is the sum of the decorrelation induced by each elementary change. In this article, we investigate the validity of this linear approximation for extended changes larger than the wavelength, and the possible signature of the change orientation. Coda waves are simulated using a 2-D finite-difference model in multiple scattering media. We perform a parametric analysis of the decorrelation induced by extended structural changes of various length and orientation, as well as the mutual influence between two identical changes separated by a varying distance. Our findings are: (1) we underestimate the length of the change when it exceeds one wavelength. (2) the decorrelation value is sensitive to the orientation of extended changes at distances smaller than four mean free paths between the source and the receiver. (3) two simultaneous changes are interacting within a distance of the order of the mean free path, but can be considered independent at a separation distance larger than a few mean free paths.     

On the various derivations of the energy dependence of the empirical optical potential

The predictions of the energy dependence of the real part of the empirical optical potential implied by the formulations based on nuclear reaction theories and on the multiple scattering approach are compared. The recent data on the nucleon-nucleon forward scattering amplitude obtained from phase-shift analyses, direct measurements and dispersion relations are used. The meaning of the local expression obtained in the multiple scattering formalism is discussed and it is shown that its implications agree with those derived by the nuclear-theories approach.     

Path-length-resolved diffusive particle dynamics in spectral-domain optical coherence tomography

We describe a new method to measure the decorrelation rate of the optical coherence tomography (OCT) magnitude simultaneously in space and time. We measure the decorrelation rate of the OCT magnitude in a Fourier-domain OCT system for a large range of translational diffusion coefficients by varying the sphere diameter. The described method uses the sensitivity advantage of Fourier-domain OCT over time-domain OCT to increase the particle diffusion imaging speed by a factor of 200. By coherent gating, we reduce the contribution of multiple scattering to the detected signal, allowing a quantitative study of diffusive particle dynamics in high concentration samples. We demonstrate that this technique is well suited to image diffusive particle dynamics in samples with a complex geometry as we measure the morphology and diffusive particle dynamics simultaneously with both high spatial and high temporal resolution.     

Particle Characterization Using Multiple Scattering Decorrelation Methods. Part 1: Standard Latex Particles

We determined the dimensions of standard polystyrene latex spheres suspended in water at different sample concentrations by dynamic light scattering and turbidimetry. Applying two different schemes for the decorrelation of multiple scattering, we show that the samples exhibit distortions of the auto-correlation function due to multiple scattering even at moderate volume fractions, which prohibits the correct determination of the particle radius. The cross-correlation functions, however, are free from these distortions. The recently deployed three-dimensional cross-correlation setup is superior to the commercially available two-color machine, as more turbid samples are accessible. In order to verify the results obtained by dynamic light scattering, we performed turbidity measurements with the same samples. This method is inherently free from multiple scattering contributions. We observe a systematically smaller radius in turbidimetry than in dynamic light scattering. The deviation, however, is only slightly outside the accuracy range of the measurements. We discuss possible origins for this deviation and show that our measurements are compatible with a hairy layer present on the particle's surface.     

M-mode swept source optical coherence tomography for quantification of salt concentration in blood: An in vitro study

We report the use of M-mode swept source optical coherence tomography (SS-OCT) for measuring sodium chloride (NaCl) salt concentrations in liquid phantoms and in drawn whole blood based on temporal dynamics of light scattering. The Brownian motion of scattering particle is affected due to the change in viscosity of liquid. An autocorrelation function was determined from the power spectrum of SS-OCT signal and then was fit by mono and double exponential function to obtain decorrelation time. These translational decorrelation times corresponding to translational diffusion coefficients enabled us to find the controlled viscosity of the medium. The viscosities of the media were compared with literature values and a fair/excellent agreement was observed. Thus, the technique has ability to quantify the salt levels in terms of viscosity in nonflowing medium suspensions and many research routes necessary to determine its potential for in-vivo applications.     

Persistent random walk model for transport through thin slabs

We present a model for transport in multiply scattering media based on a three-dimensional generalization of the persistent random walk. The model assumes that photons move along directions that are parallel to the axes. Although this hypothesis is not realistic, it allows us to solve exactly the problem of multiple scattering propagation in a thin slab. Among other quantities, the transmission probability and the mean transmission time can be calculated exactly. Besides being completely solvable, the model could be used as a benchmark for approximation schemes to multiple light scattering.     

Coherent transmission and angular structure of light scattering by monolayer films of polymer dispersed liquid crystals with inhomogeneous boundary conditions

We consider monolayer polymer films with oriented droplets of a nematic liquid crystal (LC). Relations for the coherent transmission coefficients of a layer of oriented ellipsoidal droplets and for the intensity of light scattered by monolayers of spherical and spheroidal droplets have been obtained. The amplitude-phase screen model and the interference approximation of the theory of multiple wave scattering have been used. To describe light scattering by an individual ellipsoidal droplet with inhomogeneous surface binding, we have developed an anomalous diffraction approximation. For monolayers of spherical LC droplets, the coherent scattering coefficients and the angular scattering structure have been analyzed. The internal structure of nematic droplets have been calculated by the relaxation method based on the solution of the minimization problem of the free energy volume density. We have studied basic regular features of light scattering by a monolayer with homogeneous and inhomogeneous boundary conditions at the LC-polymer interface. We show that, for films that contain droplets with inhomogeneous boundary conditions of the tangentially normal type, the angular structure of the scattered light is asymmetric with respect to the polar scattering angle.     

Real-time programmable coding metasurface antenna for multibeam switching and scanning

Novel electromagnetic wave modulation by programmable dynamic metasurface promotes the device design freedom, while multibeam antennas have sparked tremendous interest in wireless communications. A programmable coding antenna based on active metasurface elements (AMSEs) is proposed in this study, allowing scanning and state switching of multiple beams in real time. To obtain the planar array phase distribution in quick response, the aperture field superposition and discretization procedures are investigated. Without the need for a massive algorithm or elaborate design, this electronically controlled antenna with integrated radiation and phase-shift functions can flexibly manipulate the scattering state of multiple beams under field-programmable gate array (FPGA) control. Simulation and experimental results show that the multiple directional beams dynamically generated in the metasurface upper half space have good radiation performance, with the main lobe directions closely matching the predesigned angles. This metasurface antenna has great potential for future applications in multitarget radar, satellite navigation, and reconfigurable intelligent metasurfaces.     

Non-eikonal corrections in potential scattering on two centres

Scattering of a spinless projectile from a system of two (over-lapping or non-overlapping) local potentials is studied in the first-order eikonal expansion. Corrections to the Glauber formula are found to come mainly from the non-eikonal propagation in the “direct” double scattering, and not from multiple scattering (“reflections”).A comparison is made between the exact (to the leading order) and two approximate results: (i) based on the theory of scattering from non-overlapping potentials, and (ii) neglecting the reflection terms and adopting the local “Born-like” off-shell extrapolation of the two-body amplitudes. The second approximation is found to be more accurate and technically simpler in calculation of multiple scattering from many-body systems.     

Caging of particles in one-component plasmas

Strongly coupled Coulomb systems are characterized by localization ("caging") of particles trapped and oscillating in slowly fluctuating local potential wells. This observation constitutes the basic assumption underlying the quasilocalized charge approximation. Using molecular dynamics simulation we study the changes in the particles' surroundings (cages) in a classical three-dimensional one-component plasma. The results of our analysis show that at high coupling values, substantial changes occur only after several plasma oscillation cycles. We also analyze the oscillation frequencies of the caged particles and relate the decorrelation of the cages to the process of self-diffusion.     

Differential cross section,analyzing power and phase shifts for p-3He elastic scattering below 1.0 MeV

Differential cross sections and analyzing powers for the elastic scattering of polarized protons by unpolarized ³He nuclei have been measured at eight energies between 0.3 MeV and 1.0 MeV for scattering angles θ_c.m. = 52.4°–173.3°. The cross-section values were normalized to the Rutherford cross section for proton-krypton scattering. The analyzing powers have been measured with a statistical accuracy of about 0.001. The phase-shift analysis based on these data included all phases for orbital angular momenta l ≦ 1 and the channel-spin mixing parameter for the P waves. An energy parametrization of the phase shifts by an effective-range approximation allowed a simultaneous utilization of all data.     

Behaviour of scattering from a rough surface at small grazing angles

The particular problem of wave scattering at low grazing angles is of great interest because of its importance for the long-distance propagation of radio waves along the Earth's surface, radar observation of near surface objects, as well as solving many other fundamental and applied problems of remote sensing. One of the main questions is: how do the scattering amplitude and specific cross section behave for extremely small grazing angles? We consider the process of wave scattering by a statistically rough surface with the Neumann boundary condition. This model corresponds to sound scattering from a perfectly 'hard' surface (for example, the interface between air and the sea surface) or 'vertically' polarized electromagnetic waves scattered by a perfectly conducting one-dimensional (i.e. cylindrical) surface when the magnetic field vector is directed along the generating line of this cylindrical surface. We assume that the surface roughness is sufficiently small (in the sense of the Rayleigh parameter) and the surface is rigorously statistically homogeneous and therefore, infinite. We confine ourselves only to the first-order approximation of small perturbation theory and therefore consider every act of wave scattering in the Born approximation when the Bragg scattering process takes place. Only one resonant Fourier component of surface roughness is responsible for the scattering in a given direction. However, we take into account the attenuation of incident and scattered waves due to the multiple scattering processes on the path 'before' and 'after' a scattering event in a given direction. Also we consider every one of these multiple scattering events only in the Born approximation. The main result we have obtained is that for small grazing angles the scattering cross section of the diffuse component decreases as the second power of the grazing angles with respect to the incident and scattered directions, and as the fourth power of the grazing angle for the backscattering (radar) situation. Generalizing our results from plane-wave scattering to finite beams allows us to obtain the criterion on the beamwidth. For sufficiently narrow beams the multiple scattering processes do not play any role because of a short 'interaction path', and only single Bragg scattering determines the scattering amplitude (which does not tend to zero for small grazing angles). However, for sufficiently wide beams the result obtained for infinite plane waves becomes valid: due to the above-mentioned multiple scattering processes, the scattering amplitude tends to zero for small grazing angles. Consequently, the behaviour of the scattering cross section for small grazing angles depends on the radiation pattern width of the transmitting and receiving antennae: for sufficiently wide beams the scattering cross section decreases to zero at small grazing angles, but for narrow beams it tends to the finite non-zero value.     

Off-energy-shell variations of two-nucleon transition matrix and three-nucleon problem

For a schematic three-nucleon problem, we derive approximate analytic expressions for the functional derivatives of measurable three-particle quantities with respect to off-shell variations of the triplet-s, two-nucleon transition matrix. Those quantities include neutron-deuteron scattering lengths, trinucleon binding energies, and the ³He charge form-factor minimum; correlations between off-shell changes in the latter two are discussed. We indicate how results of this kind may be used to decide whether or not a given set of discrepancies between calculated and experimental three-nucleon observables can be reconciled in terms of off-shell variations of a nonretarded hermitean two-nucleon interaction. The treatment is not restricted to special classes of phase-shift equivalent potentials or phase-shift preserving transformations but instead makes use of a systematic parameterization of off-shell variations in terms of symmetric rational approximants of increasing order.     

Coherent Transmission and Reflection by a monolayer of discrete scatterers

Coherent transmission and reflection of a plane wave through a monolayer of discrete particles are considered on the basis of simple and physically transparent formulae for the single scattering approximation (SSA) corrected by introducing a multiple scattering permittivity factor. This factor allows for multiple scattering of Waves between monolayer particles, opposite to the SSA. The multiple scattering permittivity factor is considered on the basis of the quasi-crystalline approximation (QCA) via ? matrix formalism. The multiple scattering permittivity factor and parameters for obtaining coherent transmission and reflection coefficients (the effective extinction coefficient and the transmission and reflection coefficients due to rescattering) are calculated within the scope of QCA and plotted for comparison with SSA results. The expressions for these values are simplified for small Rayleigh particles to simple analytical formulae.     

Many-photon effects in inelastic light scattering

The usual approach to second harmonic generation (SHG) is based on low-order pertubation theory and neglects the changes in the electronic states that are induced by the exciting beam. To see whathappens in this approximation fails we propose a new formalism, based on the method of excitation amplitudes, to set up a theory of the SHG response and other inelastic light scattering phenomena. We develop the quantum theory in the dipole approximation and show that the inclusion of electron-photon coupling to all others leads to new features. Strong exciting fields produce a nonnegligible SHG response in highly polarisable centro-symmetric systems, and the emitted spectrum shows a dynamical Stark effect.     

Calculations on the three-nucleon system using a separable expansion of local potentials

A separable expansion for local potentials called the unitary pole expansion (UPE) has been applied to the singlet-S soft-core Reid potential. The separable potentials obtained are used in conjunction with a separable tensor potential to calculate the triton binding energy, the nd doublet scattering length and the nd phase shifts in the state above and below break up. The convergence of the UPE is good especially for repulsive terms. The one term approximation (UPA) gives a triton energy differing by 0.04 MeV and a doublet scattering length differing by 0.14 fm from the values found for the local potential. The calculated phase shifts are in good agreement with the phase-shift analysis of Van Oers and Seagrave.     

Determination of the Resultant Deflection Angle of a Particle Multiply Scattered by Nucleons of a Nucleus

The present paper considers scattering of high-energy nucleons by nuclei based on the diffraction approach that takes into account the effects of multiple scattering. The optical potential is used to describe multiple scattering in the inhomogeneous nuclear matter. A formula for the scattering wave intensity is derived in the heavy nucleus approximation. The results obtained are used to calculate the deflection angle of a charged particle multiply scattered by nucleons of a nucleus.     

Measurement of spin-correlation parameters ANN,ASS, and ASL at 2.1 GeV in proton-proton elastic scattering

At the Cooler Synchrotron COSY/Jülich spin-correlation parameters in elastic proton-proton (pp) scattering have been measured with a 2.11 GeV polarized proton beam and a polarized hydrogen atomic beam target. We report results for A(NN), A(SS), and A(SL) for c.m. scattering angles between 30 degrees and 90 degrees. Our data on A(SS)--the first measurement of this observable above 800 MeV--clearly disagrees with predictions of available pp scattering phase-shift solutions while A(NN) and A(SL) are reproduced reasonably well. We show that in the direct reconstruction of the scattering amplitudes from the body of available pp elastic scattering data at 2.1 GeV the number of possible solutions is considerably reduced.     

Light scattering in a finite multi-particle system

We use the discrete dipole approximation (DDA) to perform electromagnetic scattering calculations of particles in a 3D volume. We adjust the spacing between the particles to change the volume densities of the scattering systems from approximately 10% to 100%. For very large volume densities, e.g. >50%, it is difficult to assign unambiguously whether the system is composed of a single heterogeneous particle or of multiple particles. Our calculations demonstrate optical effects attributable to multiple scattering in systems having volume densities as high as ～90%. This suggests that heterogeneities within naturally occurring particle systems can produce multiple-scattering effects. We also see evidence of very deep negative polarization branches (NPBs) (～?6%) that may have implications in interpreting polarization phase curves of cometary circumnuclear halos.