Electromagnetic response of an array of particles: Normal-mode theory

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Abstract
A normal-mode theory for the electromagnetic excitations in an array of polarizable particles is presented. The response of the system to an external field is completely described by these modes, which are uncoupled and react independently. They are characterized by purely geometry-dependent strengths and depolarization factors. The two-sphere case is discussed in detail, and it is shown that, at small separations, excitations of pole character higher than dipole are the leading terms in the absorption spectrum.