Sergey V. Perminov

Optics of metal nanoparticle aggregates with light induced motion

Light-induced forces between metal nanoparticles change the geometry of the aggregates and affect their optical properties. Light absorption, scattering and scattering of a probe beam are numerically studied with Newtons equations and the coupled dipole equations for penta-particle aggregates. The relative changes in optical responses are large compared with the linear, low-intensity limit and relatively fast with nanosecond characteristic times. Time and intensity dependencies are shown to be sensitive to the initial potential of the aggregation forces.

Optical bistability driven by the light-induced forces between metal nanoparticles

A motion-induced optical bistability is shown for a metal nanoparticle dimer that is plasmon coupled and bound with dispersion (colloidal) forces. The effect does not require any material nonlinearity.

Polarization Effects in Nanoaggregates of Silver Caused by Local and Nonlocal Nonlinear-Optical Responses

A theoretical and experimental study is made into the combined manifestation of local and nonlocal optical responses in a cubic nonlinear isotropic medium such as an aggregated colloidal silver solution. The phenomenological treatment of polarization effects is performed for the general case with due regard for the frequency dispersion of both local and nonlocal nonlinearities and for the noncollinear propagation of pump and probe light waves. The inverse Faraday effect, the optical Kerr effect, and the self-rotation of the polarization ellipse in a fractal-disordered nonlinear medium are observed for the first time. The tensor components of the local and nonlocal cubic nonlinearities of colloidal silver solutions are measured for different degrees of aggregation. It is demonstrated that, as the size of silver aggregate increases, the nonlocal nonlinear response increases much more strongly than the local one. An inference is made that the mechanical motion of metal nanoparticles because of their dynamic interaction with the light wave field can contribute to the nonlinear polarization effects.

Giant nonlinear optical activity in an aggregated silver nanocomposite

Nonlinear optical activity due to spatial dispersion is observed in a colloidal solution of silver. It is shown experimentally that the effect is substantially enhanced (by a factor of ∼102) when the silver particles aggregate into fractal clusters. The self-rotation angle of the plane of polarization is 2 mrad at an intensity of 2 MW/cm2 for λ=0.532 μm and a pulse duration of 11 ns. A method of separating the contributions of the local and nonlocal effects to the rotation of the plane of polarization is proposed and implemented.

Nonlinear Optical Effects and Selective Photomodification of Colloidal Silver Aggregates

Colloidal silver aggregates of nanoparticles were studied experimentally using optical spectroscopy, electron microscopy, near-field optics, and nonlinear optics. Changes in absorption spectra, local structure, and near-field optical response after the irradiation of fractal colloidal aggregates with a laser pulse (selective photomodification) were studied. The diameters of the selectively photomodified domains decreased as the laser wavelength increased, in accordance with the theory of the optics of fractal clusters. Giant enhancements of nonlinear optical responses were found for aggregated nanocomposites compared with nonaggregated. The enhancements are due to excitation of the collective plasmon modes in the aggregates. The plasmon modes are anisotropic and chiral. Nonlinear effects governed by local and nonlocal responses (degenerate four-wave mixing, nonlinear absorption, refraction and gyrotropy, inverse Faraday effect, and ellipse self-rotation) were studied.

Scattering of evanescent electromagnetic waves by a cylinder near the flat boundary: the Green function and fast numerical method

The scattering of plane evanescent waves by a cylinder is studied. The Green function for the Helmholtz equation for two dielectrics with flat interface is found and applied for the numerical calculation of the scattered field by the boundary elements method. The Green function keeps close track of scattering, including multiple reflections. The result may be applicable for the data analysis in near-field optical microscopy.

Scattering of evanescent wave by two cylinders near a flat boundary

The two-dimensional problem of the evanescent wave scattering by dielectric or metallic cylinders near the interface between two dielectric media is solved. A semianalytical method involving a special Green function and a numerical solution of the boundary integral equations is proposed. A configuration with a circular and a prolate elliptic cylinders is suggested to simulate the sample and the probe in near-field optical microscopy. The far-field energy flux through the probe is calculated as a function of its position. The oscillations of the signal are interpreted as a result of the interference between evanescent and cylindrical waves.

On the Theory of Optical Properties of Fractal Clusters

A theory of optical properties of clusters of spherical metal nanoparticles characterized by an arbitrary size distribution is developed in a quasi-static dipole approximation. The equations for coupled dipoles and general relations are formulated in terms of reduced dipole moments. It is shown that the dipole resonant frequencies and amplitudes, the absorbed power, and the acting-field magnitudes strongly depend on the ratios of particle radii in a cluster. Properties of linear, planar, and three-dimensional systems are examined.

Plasmons excited by an evanescent wave in a periodic array of nanowires

Leonid L. Frumin, 2 Anton V. Nemykin, 2 Sergey V. Perminov, and David A. Shapiro 2, 4 1Institute of Automation and Electrometry, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090, Russia 2Novosibirsk State University, Novosibirsk 630090, Russia 3A.V. Rzhanov Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090, Russia 4Corresponding author: shapiro@iae.nsk.suUnusual plasmons, excited by an evanescent wave in narrow slits in a periodic array of nanowires overlying a dielectric substrate, are found from Maxwell’s equations by a modified boundary element method. The evanescent wave appears when the incident plane wave runs onto the boundary from the substrate under the angle of total internal reflection. On the basis of Floquet’s theorem, the effective Green’s function is derived by reducing the infinite structure to one elementary cell. The method is tested by simulation of the known Rayleigh–Wood’s anomalies. The plasmon resonance is found to have a sharp dependence on the angle of incidence.

Nonlinear susceptibility of a metal-dielectric nanocomposite caused by induced dipole-dipole forces between particles

The optical coefficients of a nonlinearity for a macroscopic ensemble of aggregates of metal nanoparticles that is caused by deformation of the spatial structure of clusters in a strong light field are calculated for the first time. For a continuous medium that consists of a nonabsorbing dielectric containing aggregated silver nanoparticles that do not possess an intrinsic optical nonlinearity, coefficients of nonlinear absorption are obtained in relation to the intensity and frequency of incident light. It is shown that, at intensities of up to a few megawatts per square centimeter, the addition to the absorption of a nanocomposite to be modeled is adequately described by a third-order nonlinearity. The magnitude and sign of the nonlinear absorption coefficient agree well with the previously obtained experimental data for aggregated silver and gold colloids under nanosecond excitation.