Abstract
Optical absorption cross section extrema can be investigated thoroughly for very small particles within the framework of the Rayleigh ellipsoid approximation. For an oriented ellipsoid with optical constants described by a one-oscillator Lorentz model, the frequency of maximum absorption lies between the transverse and longitudinal optical mode frequencies and depends on the particle shape and the surrounding medium; in general, the low frequency peaks are higher than the high frequency peaks. Absorption integrated over frequency for a single ellipsoid is independent of the damping constant. For randomly oriented ellipsoids, the integrated absolute maximum absorption is obtained for disks and the absolute minimum absorption for spheres. However, a sphere or any other ellipsoidal shape can be the greatest absorber at frequencies where surface modes are excited. Such surface modes are possible in the IR for particles of many common insulators: various alkali halides; oxides; carbonates; and silicates.
© 1981 Optical Society of America
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