Near-field scattering by dielectric spheroidal particles with sizes on the order of the illuminating wavelength

Abstract

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.

Near-field light focusing by wavelength-sized dielectric spheroids for photovoltaic applications

“…The solution is obtained by expanding the scattered, internal and incident fields in terms of an infinite sum of spheroidal vector wave functions whose coefficients are determined from the boundary conditions of continuity at the spheroid-medium interface. The method is described in detail in [6,7]. The coordinate system is depicted in Fig.…”

“…The code used in this work was extensively checked with known analytic and numerical solutions [7]. Here further comparisons with the electrostatic approximation (EA) and Mie theory are presented in Fig.…”

“…The bigger the particle the more modes come into play, causing the appearance of additional features in the field patterns that are highly dependent on the particle geometry and material. The peak field intensity moves from the E 0 axis to the forward direction (K 0 ) as the size increases [7]. Particles with sizes close to or above l (see R eq =l) produce transverse polarized scattered fields focused along its axis of revolution (z).…”

“…However, in most cases of practical interest scatterers are non-spherical and can be better approximated by a spheroidal shape. Therefore, here a spheroidal coordinate separation-of-variables solution [6,7] is used to explore the near-field light focusing properties of spheroidal DMPs with arbitrary size, aspect ratio and complex refractive index. The results reveal important additional possibilities relative to the particular case of spheres.…”

Nanophosphor Coatings: Technology and Applications, Opportunities and Challenges

“…At the same time, the near-field interactions become pronounced (McNeil et al, 2001). At a subwavelength distance from the particle surface, electromagnetic fields include contributions from non-propagating evanescent waves (Li et al, 2005;Mendes et al, 2010). Their influence on the radiation transfer is manifested, for example, by a phenomenon known as the frustrated total internal reflection, which causes transmission of light between two media with high refractive indices separated by a small gap filled with material of lower refractive index at the angles of incidence, for which the total internal reflection would occur in the absence of the second high-index medium.…”