Absorption Effects in Extinction

The experiments of Ashkin and Dziedzic impressively demonstrate the complexity of the electromagnetic modes of a sphere and the high degree of accuracy with which Mie theory describes them they also provide a means for measuring the sizes of single spheres to within 1 part in 105 or 106 and for sensitively monitoring small size changes. 

At this point the reader should be well aware that all solids and liquids are strongly absorbing in some spectral regions and that this has consequences for 

3 Asymmetry Associated with Narrow Absorption Bands 

Suppose that a material has a narrow, symmetric absorption band in the bulk state. It seems no more than common sense to expect that the corresponding 

Calculations for a range of particle sizes are shown in Fig. 11.13. Note that the scales have not been shifted for the different sizes extinction increases with size because of scattering. The extinction band for the 0.1-jam particle faithfully reflects the characteristics of the intrinsic absorption band. But asymmetries develop for particles larger than about 0.2 jam indeed, at a radius of 0.3 jam the absorption band looks like an emission band relative to the continuum. The explanation for this strange extinction behavior near an absorption band lies in the preceding section extinction is not a steadily increasing function of bulk absorption. A narrow absorption band is similar to a small absorption edge that falls just as rapidly as it rises, which can thus cause extinction peaks, dips, or both. 

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