Chapter XIV - SCATTERING OF WAVES IN A MEDIUM

Abstract

This chapter discusses the scattering of electromagnetic waves in a medium. It discusses linewidth in the emission spectrum and in the spectrum of scattered light. The chapter describes the combinational (Raman) scattering of light involving the formation of polaritons. It describes scattering by free electrons in a plasma and transition scattering. A medium is called homogeneous if its statistically averaged properties are independent of the coordinates. In a homogeneous medium, the average fields propagate without any scattering. The scattering by the thermal fluctuations of the permittivity does not differ from the scattering by inhomogeneities in ɛ ij produced by external sources. The normally used classical model, which serves for the description of combinational scattering of light by a molecule, is an oscillator modulating the electron polarizability α(x) of the molecule. When light is scattered in sufficiently rarefied gases, there is a characteristic independence (incoherence) of the scattering by different volumes or by different molecules. In dense gases and in condensed media, the scattering cannot be taken in different points to be independent, particularly not when analyzing the spectral composition of the scattered light.