Numerical simulation of coherent backscattering and temporal intensity correlations in random media (original) (raw)

Optical coherent backscattering by random media : an experimental study

Journal de Physique, 1988

Requ le 15 juillet 1987, accepté le 22 septembre 1987)' Résumé. 2014 Nous présentons une étude détaillée de la rétrodiffusion cohérente de la lumière par des suspensions aqueuses de microbilles de polystyrène. Nous discutons particulièrement les effets, sur la forme et la hauteur du pic de rétrodiffusion, de la taille des particules, de l'absorption 2014 contrôlée par l'addition d'un colorant 2014 et de la polarisation de la lumière. Lorsque les polarisations incidente et détectée sont parallèles, la théorie de diffusion scalaire, caractérisée par le libre parcours moyen de transport l *, rend compte de la forme du pic jusqu'à des angles de (rétro)diffusion étonnement élevés (ql * ~ 1) et de son arrondissement progressif en présence d'absorption. Nous n'observons aucune déviation à la statistique gaussienne habituelle pour le champ diffusé, et ce jusqu'à des rapports 03BB/l* ~ 0,1. Abstract. 2014 A detailed experimental study of coherent backscattering of light from aqueous suspensions of polystyrene microspheres is presented. Emphasis is on the effects of particle size, of absorption due to added dye and of light polarization on the shape and height of the backscattering cone. For parallel polarization of incident and scattered beams, the scalar diffusion theory, parametrized by the transport mean free path l*, agrees well with our data up to surprizingly large scattering angles (ql * ~ 1) and quantitatively accounts for the rounding of the cones due to absorption. No deviations from the usual Gaussian statistics of scattered fields is observed up to 03BB/l* ~ 0.1.

Modeling low-coherence enhanced backscattering using Monte Carlo simulation

Applied Optics, 2006

Constructive interference between coherent waves traveling time-reversed paths in a random medium gives rise to the enhancement of light scattering observed in directions close to backscattering. This phenomenon is known as enhanced backscattering (EBS). According to diffusion theory, the angular width of an EBS cone is proportional to the ratio of the wavelength of light to the transport meanfree-path length l s * of a random medium. In biological media a large l s * ϳ 0.5-2 mm Ͼ Ͼ results in an extremely small ͑ϳ0.001°͒ angular width of the EBS cone, making the experimental observation of such narrow peaks difficult. Recently, the feasibility of observing EBS under low spatial coherence illumination (spatial coherence length L sc Ͻ Ͻ l s *) was demonstrated. Low spatial coherence behaves as a spatial filter rejecting longer path lengths and thus resulting in an increase of more than 100 times in the angular width of low coherence EBS (LEBS) cones. However, a conventional diffusion approximation-based model of EBS has not been able to explain such a dramatic increase in LEBS width. We present a photon random walk model of LEBS by using Monte Carlo simulation to elucidate the mechanism accounting for the unprecedented broadening of the LEBS peaks. Typically, the exit angles of the scattered photons are not considered in modeling EBS in the diffusion regime. We show that small exit angles are highly sensitive to low-order scattering, which is crucial for accurate modeling of LEBS. Our results show that the predictions of the model are in excellent agreement with the experimental data.

Coherent wave backscattering by random medium. Exact solution of the albedo problem

Physics Letters A, 1990

We study the effect of coherent wave backscattering by a system of point-like scatterers. An exact solution of the albedo problem is found both for a semi-finite medium and for a random slab. It is shown that in the cases considered the diffusion approximation breaks down rapidly when oblique incidence and finite slab thickness are taken into account. It is determined that the intensity of the coherent peak tails falls off as 1 /O, where 0 is the angle between backscattering and observation directions.

Two electric field Monte Carlo models of coherent backscattering of polarized light

Journal of the Optical Society of America. A, Optics, image science, and vision, 2014

Modeling of coherent polarized light propagation in turbid scattering medium by the Monte Carlo method provides an ultimate understanding of coherent effects of multiple scattering, such as enhancement of coherent backscattering and peculiarities of laser speckle formation in dynamic light scattering (DLS) and optical coherence tomography (OCT) diagnostic modalities. In this report, we consider two major ways of modeling the coherent polarized light propagation in scattering tissue-like turbid media. The first approach is based on tracking transformations of the electric field along the ray propagation. The second one is developed in analogy to the iterative procedure of the solution of the Bethe-Salpeter equation. To achieve a higher accuracy in the results and to speed up the modeling, both codes utilize the implementation of parallel computing on NVIDIA Graphics Processing Units (GPUs) with Compute Unified Device Architecture (CUDA). We compare these two approaches through simula...

Multiple scattering model for the penetration depth of low-coherence enhanced backscattering

Journal of Biomedical Optics, 2011

Low-coherence enhanced backscattering (LEBS) is a depth-selective self-interference phenomenon that originates from light traveling time-reversed paths in a scattering medium. The depth selectivity of LEBS and its sensitivity to optical properties of the scattering medium has made it a promising technique for probing the structure of biological tissue with applications to disease diagnosis and, in particular, precancerous conditions. The ability to accurately predict the penetration depth of the LEBS signal is important in targeting an optimal tissue depth for detecting precancerous cells. This prediction is further complicated by the variation in optical properties of different tissue types. In this paper, the effects of the reduced scattering coefficient (μ s '), the phase function and the instrument spatial coherence length (L sc ) on the LEBS penetration depth are quantified. It is determined that the LEBS penetration depth is primarily dependent on L sc , μ s ', and the anisotropy factor (g), but has minimal dependence on higher moments of the phase function. An empirical expression, having a similar form as the double scattering approximation for LEBS, is found to accurately predict the average penetration depth in the multiple scattering regime. The expression is shown to be accurate for a broad range of experimentally relevant optical properties and spatial coherence lengths. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Numerical simulation of coherent effects under conditions of multiple scattering

Optics and Spectroscopy, 2004

The time correlation function and the interference component of the coherent backscattering from a multiple-scattering medium are calculated in the framework of the Monte Carlo technique. By comparing the stochastic Monte Carlo technique with the iteration procedure of solving the Bethe-Salpeter equation, it is shown that the simulation of the optical path of photon packets that have experienced n scattering events is exactly equivalent to calculating the n th-order ladder diagram. Using this equivalence, the Monte Carlo technique is generalized for simulation of the time correlation functions and coherent backscattering. © 2004 MAIK "Nauka/Interperiodica".

Electromagnetically Induced Coherent Backscattering

Physical Review Letters, 2006

We demonstrate a strong coherent backward wave oscillation using forward propagating fields only. This is achieved by applying laser fields to an ultra-dispersive medium with proper chosen detunings to excite a molecular vibrational coherence that corresponds to a backward propagating wave. The physics then has much in common with propagation of ultra-slow light. Applications to coherent scattering and remote sensing are discussed.

Coherent backscattering of circularly polarized light from a disperse random medium

To describe propagation of polarized electromagnetic wave within a disperse random medium a new Monte Carlo based technique with an adopted vector formalism has been developed. The technique has been applied for simulation of coherent backscattering of circularly polarized optical radiation from a random scattering medium. It has been found that the sign of helicity of circular polarized light does not change for a medium of point-like scatterers and can change significantly for the scatterers with the higher anisotropy. We conclude that the helicity flip of the circular polarized light can be observed in the tissue-like media. We find that this phenomenon manifests itself in case of limited number of scattering events and, apparently, can be attributed to the pulse character of incident radiation rather than to the specific form of scattering particles.

Coherent backscattering spectroscopy

Optics Letters, 2004

Coherent backscattering (CBS) of light in random media has been previously investigated by use of coherent light sources. Here we report a novel method of CBS measurement that combines low spatial coherence, broadband illumination, and spectrally resolved detection. We show that low spatial coherence illumination leads to an anomalously broad CBS peak and a dramatic speckle reduction; the latter is further facilitated by low temporal coherence detection. Thus CBS can be observed in biological tissue and other media that previously were beyond the reach of conventional CBS measurements. We also demonstrate, for the first time to our knowledge, spectroscopic analysis of CBS. CBS spectroscopy may find important applications in probing random media such as biological tissue in which depth-selective measurements are crucial.

Theoretical study of the coherent backscattering of light by disordered media

Journal de Physique, 1988

2014 Nous présentons une étude théorique de la rétrodiffusion cohérente de la lumière par un milieu désordonné dans diverses situations incluant les effets dépendant du temps, les milieux absorbants et les effets liés à la modulation d'amplitude de la lumière. Nous discutons tout particulièrement le cas de la diffusion anisotrope et les effets de la polarisation afin d'expliquer quantitativement les résultats expérimentaux. Nous donnons un calcul microscopique de l'albedo cohérent afin de justifier la relation heuristique précédemment établie. Nous prédisons aussi la forme de l'albedo cohérent d'un milieu fractal. Enfin, la validité des différentes approximations utilisées est discutée et quelques développements ultérieurs sont évoqués. Abstract. 2014 A theoretical study of the coherent backscattering effect of light from disordered semi-infinite media is presented for various situations including time-dependent effects as well as absorption and amplitude modulation. Particular attention is devoted to the case of anisotropic scattering and to polarization in order to explain quantitatively experimental results. A microscopic derivation of the coherent albedo is given which strongly supports the heuristic formula previously established. In addition the coherent albedo of a fractal system is predicted. The validity of the different approximations used are discussed and some further theoretical developments are presented.