A previously developed theoretical method for determining the electromagnetic fields for arbitrary monochromatic light incident on an irregularly shaped particle, the boundary-matching method, is used to investigate the effects of small surface perturbations on the quality Q and the focused-beam excitation of resonances in microspheres. Axisymmetric particles with periodic surface roughness and irregular surface roughness are considered. For a given resonance the resonance Q is found to be relatively unaffected by the presence of the surface perturbations until the surface perturbation amplitude ε reaches a threshold value, beyond which the Q decreases rapidly with increasing ε. For the perfect sphere, focused-beam excitation of the resonance is most efficient with the beam focused outside the surface of the sphere at a location consistent with the prediction of van de Hulst’s localization principle. However, calculations indicate that, for conditions under which the surface perturbation amplitude is large enough to appreciably decrease the resonance Q, focused-beam excitation of the resonance is most efficient with the beam focused just inside the particle surface.
© 1999 Optical Society of America
(260.2110) Physical optics : Electromagnetic optics
(260.5740) Physical optics : Resonance
(290.0290) Scattering : Scattering
(290.4020) Scattering : Mie theory
(290.5850) Scattering : Scattering, particles
John P. Barton, "Effects of surface perturbations on the quality and the focused-beam excitation of microsphere resonance," J. Opt. Soc. Am. A 16, 1974-1980 (1999)