Arrays Of Small Particles Research Articles

Scattering-matrix analysis of nanoparticle lattices in dipole approximation

Fourier modal method (FMM) proved itself as an effective technique for investigation of layered periodic structures. However, it fails to deal with arrays of small particles because of high gradients in a local field. In this paper, we demonstrate the capability of the method, which is based on the construction of scattering matrices of arrays of resonant nanoparticles semianalytically in discrete dipole approximation (DDA). This approach is much faster than conventional ones and therefore provides an opportunity for thorough consideration of various layered structures with small periodic inclusions in terms of the RCWA. The performance of the considered method is demonstrated on an example of plasmonic lattices embedded in a homogeneous ambience and placed inside and onto an optical waveguide. Localized surface plasmon resonances (LSPRs), lattice plasmon resonances (LPRs) and their hybridization with photonic guided modes are observed. High precision of this calculations is confirmed by comparison with finite element method (FEM).

Fourier modal method for the description of nanoparticle lattices in the dipole approximation

Rigorous coupled-wave analysis (RCWA) is a very effective tool for the studying optical properties of multilayered vertically invariant periodic structures. However, it fails to deal with arrays of small particles because of high gradients in a local field. In this thesis, we implement discrete dipole approximation (DDA) for the construction of scattering matrices of arrays of resonant nanoparticles. This strongly speeds up the calculations and therefore provides an opportunity for thorough consideration of various layered structures with small periodic inclusions in terms of the RCWA. We study in detail three main stages of the method: calculation of polarizability tensor of a single nanoparticle, effective polarizability of this particle in a lattice and corresponding scattering matrix of the layer for further integration in the conventional RCWA approach. We demonstrate the performance of the proposed method by considering plasmonic lattices embedded in a homogeneous ambiance and placed inside and onto optical waveguides and compare our results with experimental papers. Such phenomena as localized surface plasmon resonances (LSPRs) and lattice plasmon resonances (LPRs) are observed as well as their hybridization with photonic guided modes. High accuracy and fast convergence of our approach are shown by a comparison with other computational approaches. Typical limits of applicability of our approximate method are determined by an exploration of the dependence of its error on the parameters of the structure.

Tailoring Reflections From Thin Composite Metamirrors

We propose an effective route to fully control the phase of plane waves reflected from electrically (optically) thin composite sheets. This becomes possible using engineered artificial full-reflection layers (metamirrors) formed by arrays of electrically small resonant bi-anisotropic particles. In this scenario, fully reflecting mirrors do not contain any continuous ground plane, but only arrays of small particles. Bi-anisotropic omega coupling is required to get asymmetric response in reflection phase for plane waves incident from the opposite sides of the composite mirror. It is shown that with this concept one can independently tailor the phase of electromagnetic waves reflected from both sides of the mirror array.

Extraordinary Absorption of Decorated Undoped Graphene

We theoretically study absorption by an undoped graphene layer decorated with arrays of small particles. We discuss periodic and random arrays within a common formalism, which predicts a maximum absorption of 50% for suspended graphene in both cases. The limits of weak and strong scatterers are investigated, and an unusual dependence on particle-graphene separation is found and explained in terms of the effective number of contributing evanescent diffraction orders of the array. Our results can be important to boost absorption by single-layer graphene due to its simple setup with potential applications to light harvesting and photodetection based on energy (Förster) rather than charge transfer.

Synthesis of Polarization Transformers

We study the possibility of analytically synthesizing different polarization-transforming devices realized as arrays of small particles. The proposed method is based on general relations between the reflection and transmission coefficients and the polarizabilities of arbitrary bi-anisotropic particles. As an example, we reveal all possible types of inclusions which can be used to realize twist polarizers, select one of them and synthesize a novel twist polarizer. The synthesized twist polarizer is then fitted on a standard printed circuit board, optimized numerically, and finally manufactured and measured. The experimental results for the twist polarizer show good correspondence with the simulations and the new method is found to be a useful tool for developing any polarization-transforming devices. As one more example, a novel circular polarization selective surface is synthesized.

Switching properties of a regular two-dimensional array of small uniaxial particles

Switching properties of a regular square lattice of 40/spl times/40/spl times/3 /spl mu/m/sup 3/ highly uniaxial, single domain magnetic garnet pixels have been measured magnetooptically. "Up" and "down" switching fields, coercivities and interaction fields were measured on an assembly of hundreds of particles. Statistical analysis of the data shows the relationship between major loop parameters and mean values of the distributions. Local demagnetizing tensor elements were calculated for the non-ellipsoidal geometry and the interaction fields from different neighbors were computed. The importance of the effect of the geometry, shape and size of particles on the switching properties is demonstrated. The agreement with experimental values is very good. The simplicity of this model system is attractive for studying artificially structured 2-D arrays of small particles.

Interaction effects in switching of a two dimensional array of small particles

The magnetostatic interaction between elements of a regular two-dimensional array of rectangular garnet pixels has been investigated. The up- and down switching fields of an individual pixels, have been measured magnetooptically. The switching characteristics of a given pixel depends on the state of the neighbors. In this work the effect of the magnetization state of the first 5 coordination shells on a central, test pixel was investigated experimentally and numerically. The interaction field, i.e. the demagnetizing/magnetizing effects, is calculated exactly and in the dipole approximation for 24 pixels surrounding the central pixel. A good agreement between experimental and numerical results has been obtained.

Freeze-fracture cytochemistry of sympathetic ganglia. Distribution of filipin and tomatin induced membrane deformations in neurons and satellite cells.

Application of filipin to sympathetic ganglia results in membrane deformations in both the neurons and the satellite cells. The plasma membranes of the principal ganglion cells show a non-homogeneous distribution of filipin induced deformations with fewer deformations in the perikaryal plasma membrane than in the nerve fiber membrane. The filipin induced membrane lesions are correlated to the number of IMPs of the neuronal membrane i.e. a high density of intramembrane particles (IMP) gives fewer deformations and vice versa. The membrane of the satellite cells contain a higher density of probe induced lesions than the neuronal membrane. The filipin induced deformations in the satellite cells are not correlated to the number of IMPs or to the number of orthogonal arrays of small particles (OAP). Specialized membrane areas such as the gap junction is always devoided of filipin induced lesions. A similar distribution of membrane lesions was found when tomatin was used instead of filipin. These results indicate a possible difference in lipid content between various parts of the neurons and between the neuronal and satellite cell plasma membrane in guinea pig sympathetic ganglia.