Extinction A Synopsis

Mie theory does an admirable job of predicting extinction by spherical particles with known optical constants even the finest details it predicts—ripple structure—have been observed in extinction by single spheres. Several different causes—a distribution of sizes or shapes, and absorption—have the same effect of effacing the ripple structure or even the broader interference structure. 

Absorption dominates over scattering for sufficiently small absorbing particles. Volumetric extinction by such particles is independent of their size but not of their shape we shall discuss shape effects further in the following chapter. 

Extinction is frequently dominated by scattering if the particle is about the same size as or larger than the wavelength. But absorption, which is usually manifested by absorption bands or absorption edges, can strongly affect extinction in unexpected ways extinction may either increase or decrease with 

Extinction is easy to measure in principle but may be difficult in practice, especially for large particles where it becomes difficult to discriminate between incident and forward-scattered light. Spheres and ensembles of randomly oriented particles do not linearly polarize unpolarized light upon transmission. But single elongated particles or oriented ensembles of such particles can polarize unpolarized light by differential extinction. 

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