Morphology-dependent resonances in an eccentrically layered sphere illuminated by a tightly focused off-axis Gaussian beam: parallel and perpendicular beam incidence

Following the recent results in generalized Lorenz-Mie theory concerning the description of an arbitrary shaped electromagnetic beam propagating in an arbitrary orientation, a theoretical investigation of morphology-dependent resonances (MDRs) excited in a sphere with an eccentrically located spherical inclusion illuminated by a tightly focused Gaussian beam is presented. Calculations of extinction efficiency spectra and backward-scattering intensity spectra are made for different locations and radii of the inclusion with respect to the host sphere. Exemplifying field distributions inside of the scatterer under both off-resonance and on-resonance conditions are exhibited. The influences of the relative size of the inclusion with respect to the host sphere and of the separation distance between the two sphere centers on the positions and on the amplitudes of the MDRs peaks are studied. As are the cases for spheres and concentrically multilayered spheres, the resonance positions of MDRs in an eccentrically layered sphere are located at the same size parameter for Gaussian beam illumination and for plane-wave illumination. In contrast with the lift of azimuthal modes m degeneracy in MDR peaks for an eccentric sphere illuminated obliquely by a plane wave, we display a kind of lift that cannot be observed in extinction efficiency spectra with an oblique illumination of a tightly focused Gaussian beam. Nevertheless, asymmetric distributions of the internal field inside of the eccentric sphere at resonance conditions are observed both with an oblique illumination of a tightly focused beam and with an oblique illumination of a plane-wave illumination. Interpretation from a perspective of the localization principle is applied to the simulation results. (C) 2011 Optical Society of America