Elena Eremina

Single-particle evanescent light scattering simulations for total internal reflection microscopy.

We simulate and measure light scattering of a micrometer-sized spherical particle suspended in solution close to a glass substrate. The model, based on the discrete sources method, is developed to describe the experimental situation of total internal reflection microscopy experiments; i.e., the particle is illuminated by an evanescent light field originating from the glass-solvent interface. In contrast to the well-established assumption of a simple exponential decay of the scattering intensity with distance, we demonstrate significant deviations for a certain range of penetration depths and polarization states of the incident light.

Simulation of light scattering by biconcave Cassini ovals using the nullfield method with discrete sources

In this paper the nullfield method with discrete sources (NFM-DS) is applied to analysis of light scattering by biconcave Cassini-like particles, which can be described as oblate discspheres with central concavities on their top and bottom. As far as we know this is a first attempt to apply a modification of the T-matrix method to model such a nonconvex object. The numerical results for different particles under different incident angles obtained by the NFM-DS are presented in the last section of the paper. For result verification the discrete source method (DSM) has been chosen. The comparison of results obtained by using both methods shows very good agreement.

Comparison of the discrete dipole approximation and the discrete source method for simulation of light scattering by red blood cells.

The discrete sources method (DSM) and the discrete dipole approximation (DDA) were compared for simulation of light scattering by a red blood cell (RBC) model. We considered RBCs with diameters up to 8 mum (size parameter up to 38), relative refractive indices 1.03 and 1.06, and two different orientations. The agreement in the angle-resolved S(11) element of the Mueller matrix obtained by these methods is generally good, but it deteriorates with increasing scattering angle, diameter and refractive index of a RBC. Based on the DDA simulations with very fine discretization (up to 93 dipoles per wavelength) for a single RBC, we attributed most of the disagreement to the DSM, which results contain high-frequency ripples. For a single orientation of a RBC the DDA is comparable to or faster than the DSM. However, the relation is reversed when a set of particle orientations need to be simulated at once. Moreover, the DSM requires about an order of magnitude less computer memory. At present, application of the DSM for massive calculation of light scattering patterns of RBCs is hampered by its limitations in size parameter of a RBC due to the high number of harmonics used for calculations.

Total internal reflection microscopy with a multilayered interface: a light scattering model based on a discrete sources method

The discrete sources method has been extended to analyse P or S polarized evanescent wave scattering by a dielectric particle located on a layered interface. This was done to develop a light scattering simulation model for total internal reflection microscopy. The influence of metallic layers on the prism surface is investigated. Numerical results for the objective response versus particle height and the scattering cross-section are presented.

Computational nano-optic technology based on discrete sources method

Continuous advance in the potential of fabrication and utilization of nanostructures for different applications requires an adequate tool for such structures’ analysis and characterization. Investigation of light scattered by nanostructures by means of computer simulation seems to be a reliable tool for investigation of the properties and functional abilities of nanostructures. In particular, nano-features embedded in layered structures are of growing interest for many practical applications. Mathematical modeling of light scattering allows us to predict functional properties and behavior of nanostructures prior to their fabrication. This helps to reduce manufacturing and experimental costs. In the present paper, the Discrete Sources Method (DSM) is used as a tool of computational nano-optics. Mathematical models based on DSM are used for several practical applications. We are going to demonstrate that the computer simulation analysis allows not only prediction and investigation of the system properties, but can help in development and design of new setups.

Extension of the discrete sources method to light scattering by highly elongated finite cylinders

Abstract Light scattering by long finite cylinders is applied for particle characterization, investigation of scattering and absorption properties of interstellar dust, ice crystals and many other fields. In recent years many methods have been used to solve this problem, but usually their applicability is restricted to aspect ratios of about 10. In this paper a renewed algorithm of the discrete sources method is described, which allows computer simulation of light scattering by highly elongated cylinders with aspect ratios up to 100 and length up to 40 μm.

Analysis of the extreme scattering effect for particles inside and above a noble metal film via the discrete sources method

In this paper the discrete sources method is applied to analyze the extreme scattering effect for particles located both inside and on a gold film deposited on a glass prism. The extreme scattering effect is an effect of the sharp increase of the scattered intensity for P-polarized excitation which occurs in the evanescent wave region behind the critical angle. Moreover, the intensity enhancement appears not only in the transmission direction but in the backscattering direction as well. The effect does not depend on the thickness of the metal film or particle diameter, but it is strongly affected by the film material. Different scattering characteristics, such as transmission cross section and reflection cross sections and their correlation with the surface plasmon resonance in the film, are investigated and discussed in this paper. The analysis of the influence of a thin transparent spacer layer between particle and gold film on the scattering characteristics has been performed. The differential scattering cross section is considered to examine the field distribution in the forward and backscattering directions.

Analysis of plasmonic resonances of two paired noble metal spheroids via the discrete sources method

A modified scheme of the discrete sources method has been applied to investigate the strong interaction between proximal noble metal nanoparticles. The new scheme enables calculation of a near-field enhancement of several orders with a high degree of accuracy. The total field enhancement in between two spheroidal particles and the scattering cross-section have been analyzed in the frequency domain depending on the separation distance, spheroid aspect ratio, equivolume diameter, and material. In particular, it has been found that spheroids of smaller size can produce larger field enhancement than larger ones. Simulation results demonstrate that it is possible to achieve localized surface plasmon resonance at any desired exciting wavelength by using an appropriate geometrical configuration and material of the coupled spheroids.

New scheme of the Discrete Sources Method for investigation of a near field enhancement by coupled particles

Article history: Numerical scheme of the Discrete Sources Method has been modified to examine near fields for the polarized light scattering by two coupled noble metal particles. The new scheme enables to compute a near field enhancement of several orders with high accuracy degree. The developed computer model has been employed to investigate plasmonic resonance of two prolate spheroids. Both the electric field intensity between coupled particles and the Scattering Cross-Section have been examined versus particle distance and particles aspect ratio.

Analysis of Evanescent Waves Scattering by a Single Particle in Total Internal Reflection Microscopy

Since its invention in the mid of eighties (1) Total Internal Reflection Microscopy (TIRM) has proven to be an effective technique to measure weak interactions between spherical colloidal particles and surfaces with a resolution of a few femtonewton. It is a single particle evanescent light scattering technique. In an experimental setup a laser beam is coupled into a prism and hits the glass-water interface with an angle slightly above the critical angle of total internal reflection. This generates an evanescent field near the interface that decays in the lower refractive index medium (water) with a characteristic penetration depth which depends on the angle of incidence. A colloidal particle that is dispersed in the medium will scatter light from the evanescent wave if it is in the vicinity of the surface. By registering a scattered intensity it is possible to deduce the particle- substrate distance. Compared to other methods for measure particle wall interactions like the surface force apparatus or the atomic force microscopy where a colloidal particle is attached to the tip, TIRM is the most sensitive technique because thermal fluctuations where limit the other methods in their resolution are exploited to determine the interaction potential. In this way forces in the order of a few femtonewton can be detected. TIRM has proven to be a valuable tool for the precise measurement of weak colloidal interactions as double layer forces, van der Waals forces, magnetic interactions and depletion forces. Review on TIRM can be found for example in (2,3). To compare experimental results with results of mathematical modeling an effective light scattering method is needed. For this purpose the Discrete Sources Method (DSM) has been chosen. The DSM is a well-known method for light scattering analysis, which has recently been applied for evanescent wave scattering (4). 1. Discrete Sources Method For the theoretical modeling the Discrete Sources Method (DSM) has been chosen. The DSM is a well-known method for the analysis of light scattering. It has recently been applied to the evanescent wave scattering (4). In frame of the DSM the mathematical statement can be presented as follows: