Electric Field Monte Carlo Simulation Research Articles

Separating single- and multiple-scattering components in laser speckle contrast imaging of tissue blood flow.

Random matrix theory provides new insights into multiple scattering in random media. In a recent study, we demonstrated the statistical separation of single- and multiple-scattering components based on a Wishart random matrix. The first- and second-order moments were estimated with a Wishart random matrix constructed using dynamically backscattered speckle images. In this study, this new strategy was applied to laser speckle contrast imaging (LSCI) of in vivo blood flow. The random matrix-based method was adopted and parameterized using electric field Monte Carlo simulations and in vitro blood flow phantom experiments. The new method was further applied to in vivo experiments, demonstrating the benefits of separating the single- and multiple-scattering components, and the method was compared with the traditional temporal laser speckle contrast analysis (LASCA) method. More specifically, the new method separates the stimulus-induced functional changes in blood flow and tissue perfusion in the superficial (<2l t , l t is the transport mean free path) and deep layers (1l t ∼ 7l t ), extending LSCI to the evaluation of functional and pathological changes.

Random matrix description of dynamically backscattered coherent waves propagating in a wide-field-illuminated random medium

The wave propagation in a random medium plays a critical role in optics and quantum physics. Multiple scattering of a coherent wave in a random medium determines the transport procedure. Brownian motions of scatterers perturb each propagation trajectory and form dynamic speckle patterns in the backscattered direction. In this study, we applied the random matrix theory to investigate the eigenvalue density of the backscattered intensity matrix. We find that the dynamic speckle patterns can be utilized to decouple the single and multiple backscattered components. The Wishart random matrix of the multiple scattering component is well described by the Marčenko–Pastur law, while the single scattering part has a low-rank characteristic. We, therefore, propose a strategy for estimating the first and second order moments of single and multiple scattering components, respectively, based on the Marčenko–Pastur law and trace analysis. Electric field Monte Carlo simulation and in vivo experiments demonstrate its potential applications in hidden absorbing object detection and blood flow imaging. Our method can be applied to other coherent domain elastic scattering phenomena for wide-field propagation of microwave, ultrasound, etc.

Reverse electric field Monte Carlo simulation for vector radiative transfer in the atmosphere

In this paper, a reverse electric field Monte Carlo (REMC) method is proposed to study the vector radiation transfer in the atmosphere. The REMC is based on tracing the multiply scattered electric field to simulate the vector transmitted radiance. The reflected intensities with different total optical depth values are obtained, which accord well with the results in the previous research. Stokes vector and the degree of polarization are numerically investigated. The simulation result shows that when the solar zenith angle is determined, the zenith angle of detector has two points, of which the degree of polarization does not change with the ground albedo and the optical depth. The two points change regularly with the solar zenith angle. Moreover, our REMC method can be applied to the vector radiative transfer in the atmosphere—ocean system.

Electric field Monte Carlo simulation of focused stimulated emission depletion beam, radially and azimuthally polarized beams forin vivodeep bioimaging

An electric field Monte Carlo method is used to study the focal spot of a stimulated emission depletion (STED) beam, radially and azimuthally polarized beams in a turbid medium as a function of the scattering coefficient. To consider the diffraction of light of the wave nature, the wavefront is decomposed into a set of secondary spherical subwaves according to the Huygens principle. From the simulation results, we can find that the STED beam can still form a doughnut focal spot inside the turbid medium. These simulation results are important for the feasibility study of STED microscopy for in vivo deep bioimaging. Similarly, the focal spot for an azimuthally polarized beam can also keep a doughnut spot at the focal plane in a turbid medium.

VECTORIAL ELECTRIC FIELD MONTE CARO SIMULATIONS FOR FOCUSED LASER BEAMS (800 NM-2220 NM) IN A BIOLOGICAL SAMPLE

Here we develop a method that combines vectorial electric field Monte Carlo simulation with Huygens-Fresnel principle theory to determine the intensity distribution of a focused laser beam in a bio ...

Open source software for electric field Monte Carlo simulation of coherent backscattering in biological media containing birefringence

ABSTRACT. We present an open source electric field tracking Monte Carlo program to model backscattering in biological media containing birefringence, with computation of the coherent backscattering phenomenon as an example. These simulations enable the modeling of tissue scattering as a statistically homogeneous continuous random media under the Whittle-Matérn model, which includes the Henyey-Greenstein phase function as a special case, or as a composition of discrete spherical scatterers under Mie theory. The calculation of the amplitude scattering matrix for the above two cases as well as the implementation of birefringence using the Jones N-matrix formalism is presented. For ease of operator use and data processing, our simulation incorporates a graphical user interface written in MATLAB to interact with the underlying C code. Additionally, an increase in computational speed is achieved through implementation of message passing interface and the semi-analytical approach. Finally, we provide demonstrations of the results of our simulation for purely scattering media and scattering media containing linear birefringence.

GPU accelerated electric field Monte Carlo simulation of light propagation in turbid media using a finite-size beam model

An electric field Monte Carlo (EMC) simulation directly traces the complex electric field vectors in multiple scattering and estimates the electric field in a preferred direction. The full vectorial nature of EMC makes it a powerful and flexible tool to simulate the coherence and polarization phenomena of light. As a numerical method, EMC needs to launch a large number of photons to achieve an accurate result, making it time-consuming. Previously, EMC did not account for the beam size. Because of the stochastic character of the instantaneous electric field in the simulation, the convolution method alone is unsuitable for the Monte Carlo simulation of photon energy for a beam with a finite size. It is necessary to launch photons from all possible locations to simulate a finite-size beam, which results in a significant increase in the computational burden. In order to accelerate the simulation, a parallel implementation of the electric field Monte Carlo simulation based on the compute unified device architecture (CUDA) running on a graphics processing unit (GPU) is presented in this paper. Our program, which is optimized for Fermi architecture, is able to simulate the coherence phenomenon of a finite-size beam normally incident on turbid media. A maximum speedup of over 370x is achieved with a GTX480 GPU, compared with that obtained using an Intel i3-2120 CPU.

Electric field Monte Carlo simulations of focal field distributions produced by tightly focused laser beams in tissues.

The focal field distribution of tightly focused laser beams in turbid media is sensitive to optical scattering and therefore of direct relevance to image quality in confocal and nonlinear microscopy. A model that considers both the influence of scattering and diffraction on the amplitude and phase of the electric field in focused beam geometries is required to describe these distorted focal fields. We combine an electric field Monte Carlo approach that simulates the electric field propagation in turbid media with an angular-spectrum representation of diffraction theory to analyze the effect of tissue scattering properties on the focal field. In particular, we examine the impact of variations in the scattering coefficient (µs), single-scattering anisotropy (g), of the turbid medium and the numerical aperture of the focusing lens on the focal volume at various depths. The model predicts a scattering-induced broadening, amplitude loss, and depolarization of the focal field that corroborates experimental results. We find that both the width and the amplitude of the focal field are dictated primarily by µs with little influence from g. In addition, our model confirms that the depolarization rate is small compared to the amplitude loss of the tightly focused field.

Amplitude and Phase of Tightly Focused Laser Beams in Turbid Media

A framework is developed that combines electric field Monte Carlo simulations of random scattering with an angular-spectrum representation of diffraction theory to determine the amplitude and phase characteristics of tightly focused laser beams in turbid media. For planar sample geometries, the scattering-induced coherence loss of wave vectors at larger angles is shown to be the primary mechanism for broadening the focal volume. This approach for evaluating the formation of the focal volume in turbid media is of direct relevance to the imaging properties of nonlinear coherent microscopy, which rely on both the amplitude and phase of the focused fields.

Electric field Monte Carlo simulation of coherent backscattering of polarized light by a turbid medium containing Mie scatterers

A method for directly simulating coherent backscattering of polarized light by a turbid medium has been developed based on the Electric field Monte Carlo (EMC) method. Electric fields of light traveling in a pair of time-reversed paths are added coherently to simulate their interference. An efficient approach for computing the electric field of light traveling along a time-reversed path is derived and implemented based on the time-reversal symmetry of electromagnetic waves. Coherent backscattering of linearly and circularly polarized light by a turbid medium containing Mie scatterers is then investigated using this method.

Electric field Monte Carlo simulation of polarized light propagation in turbid media

A Monte Carlo method based on tracing the multiply scattered electric field is presented to simulate the propagation of polarized light in turbid media. Multiple scattering of light comprises a series of updates of the parallel and perpendicular components of the complex electric field with respect to the scattering plane by the amplitude scattering matrix and rotations of the local coordinate system spanned by the unit vectors in the directions of the parallel and perpendicular electric field components and the propagation direction of light. The backscattering speckle pattern and the backscattering Mueller matrix of an aqueous suspension of polystyrene spheres in a slab geometry are computed using this Electric Field Monte Carlo (EMC) method. An efficient algorithm computing the Mueller matrix in the pure backscattering direction is detailed in the paper.