Scattering

Abstract

In the preceding chapters, we have described quantitatively the propagation of radiation from its source to a receiver using two quantities, usually the refractive index n and the extinction coefficient k. Within a qualitative description, the phenomena related to diffuse reflection and scattering were also considered. Both play an important role in optics. They lead us to the concept of a light beam and its graphical representation using ‘light rays’ drawn as straight lines. Diffuse reflection and scattering allow objects that themselves do not emit light to become visible as “secondary emitters”. The treatment of some important diffraction and interference phenomena is based upon them. Scattering allows us to identify polarized light through its asymmetry (Fig. 24.4).

These examples however by no means exhaust the significance of scattering. Scattering leads to a whole series of other important insights, for example in connection with refraction and dispersion (Chap. 27). This is why we want to treat the topic of scattering more comprehensively in this chapter.

The fundamental aspects of scattering have already been illustrated by demonstration experiments in earlier chapters. Their qualitative interpretation makes use of the analogy to water waves: An obstacle which is small compared to the wavelength, e.g. a rod, is encountered by a wave train. The obstacle then becomes the source of a new, “secondary” wave train which propagates in all directions away from it (Vol. 1, Fig. 12.17).