Optical Excitation of Quadrupole Plasma Oscillations in Ellipsoidal Particles
The optical properties of thin granular films and colloids are usually described by means of the “dipole approximation”, assuming that the light acts on ellipsoidal particles of extremely small dimensions compared to the wavelength of the incident light, A first order correction of this theory is obtained by considering somewhat larger ellipsoidal particles, so that the electric field of the incident light wave varies linearly instead of being constant in the vicinity of the particle. This leads actually to very concise analytical expressions, with well defined form factors for the corresponding quadrupole effects, when the directions of polarization and propagation of the light wave are specified with respect to the equatorial plane of arbitrarily shaped spheroidal particles. A more general expression for the effective dielectric constant of an ensemble of equally oriented spheroids can thus also be established.
KeywordsEquatorial Plane Optical Excitation Dipole Approximation Oblate Spheroid Effective Dielectric Constant
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