Light scattering by nanosized systems with different spatial organizations (original) (raw)
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The geometrical nature of optical resonances in nanoparticles
We give a geometrical theory of resonances in Maxwell's equations that generalizes Mie formulae for spheres to any dielectric or metallic particle without sharp edges. We show that the electromagnetic response of a particle is given by a set of modes of internal and scattered fields and reveal a strong analogy between resonances in nanoparticles and excess noise in unstable macroscopic cavities. We give examples of two types of optical resonances: those in which a single pair of internal and scattered modes become strongly aligned in the sense defined in this paper, and those resulting from constructive interference of many pairs of weakly aligned modes, an effect relevant for sensing. We demonstrate that modes can be either bright or dark depending on the incident field and give examples of how the excitation can be optimized. Finally, we apply this theory to gold particles with shapes often used in experiments.
Configurational resonances phenomena in optical scattering spectroscopy of nano-objects
2002
The light scattering from a nano-sized object formed by two or three dipole atoms (polarizable components) is studied in detail using a microscopic approach. The atoms are considered to be linear Lorenz oscillators interacting via the electromagnetic field only. For simple configuration of nano-object, the self-consistent electromagnetic problem is solved analytically. It is shown that the near-field interaction between the dipole atoms can give rise to a dramatic modification of the polarizing characteristics of atoms and the total polarizability of nano-object. We point out the existence of a number of resonance peaks in the frequency dependences. The shift of resonance peaks from the position of the resonances corresponding to the isolated atoms depends mainly on the interatomic distances and can significantly exceed the natural linewidth. Generally, the resonance characteristics of atoms depend on various system parameters such as the atomic polarizabilities (i.e. the eigenfrequencies), the number of atoms, and the interatomic distances. The scattered light intensity detected in wave zone is shown to depend essentially on the configuration of nano-object, the light frequency, polarization, and direction of external wave.
Experimental observation of the scattering of light by planar metallic nanoparticles
New Journal of Physics, 2003
It is known that the efficiency of scattering of light by a particle is related to its size, geometry and optical constants of the material, since the theory of scattering by small particles developed by Mie in the beginning of the 20th century. However, the Mie scattering theory is valid just for a few special cases like a homogeneous sphere embedded on a medium of homogenous refraction index. More recently, some theoretical simulations on planar nanoparticles have shown that the optical resonances are dependent on the shape of the particle. Simultaneously, local field enhancements take place on the particles when excited by an incident wave.
Journal of the Optical Society of America B, 2010
We present a theoretical study of electric field scattering by wavelength-sized spheroids. The incident, internal, and scattered fields are computed analytically by a spheroidal coordínate separation-of-variables solution, assuming axially incident monochromatic illumination. The main sources of possible numerical errors are identified and an additional point-matching procedure is implemented to provide a built-in test of the validity of the results. Numerical results were obtained for prolate and óblate particles with particular aspect ratios and sizes, and a refractive índex of 1.33 relative to the surrounding médium. Special attention is paid to the characteristics of the near-field in cióse proximity to the spheroids. It is shown that particles with sizes cióse to the incident wavelength can produce high field enhancements whose spatial location and extensión can be controlled by the particle geometry.
Journal of the Optical Society of America, 1978
Mie scattering theory is used to calculate the efficiency factors for absorption by microscopic dielectric spheres. Resonances in the efficiency factors for absorption and resonances in the amplitudes of the electric and magnetic multipoles which occur in an expansion of the fields inside the dielectric sphere are discussed. Several trends in the strengths and width of the various resonances as functions of the absorption coefficient of the sphere, size parameter, multipole order, and multipole resonance number are given. A formal solution for elastic (Mie) and inelastic (Raman) scattering by microscopic particles is derived from the extinction theorem. With this background, some implications of the resonances in the interpretation of absorption, fluorescence, and Raman scattering by microscopic particles are discussed.
Revista Mexicana de Física
We study the diffraction of a monochromatic electromagnetic plane wave by a dielectric&metal-core/metal-shell nanoparticle surrounded by a dielectric medium. This problem was solved by using generalized Mie’s theory and both the scattering cross section and the square module of the electric field were calculated as a function of shell thickness. Numerically, the first particles studied were gold-core/silver-shell nanoparticles and their inverse configuration. The gold-core/silver-shell particle presented more variation of their optical properties. The second particles were vacuum-core/metal-shell surrounded by vacuum, symmetric configurations. In this case, the dispersive Drude dielectric function for the metal was used, and a comparative study between the positions of the resonance frequencies obtained from quasi-static limit and electrodynamic theory was performed. Thus, consequently the formula obtained from the quasi-static limit can be used to calculate the positions of the res...
Theory of resonances in the electromagnetic scattering by macroscopic bodies
Physical Review B, 1980
The electromagnetic scattering resonances of a collection of macroscopic bodies with uniform electric properties are used to construct a spectral representation for the scattered field. The resonances and their weights are found by solving for the eigenvalues and eigenstates of a non-Hermitian, linear integral operator I. A scheme is developed for doing this by diagonalizing a matrix that represents I' by the set of individual grain eigenstatesthe diagonal elements are individual grain eigenvalues while the off-diagonal elements are overlap integrals of eigenstates from two different grains. For a system of spherical scatterers, this scheme leads to a reasonable method of calculating numerically the scattered field in cases where the multiple scattering is important. As an example, the scattering by a pair of identical spheres is worked out analytically for a limiting case. Sum rules for the weights in the spectral representation are derived and discussed.