Many aspects of the interaction between radiation and matter can be described quite accurately by a classical theory in which the medium is represented by model atoms consisting of positive and negative parts bound by an attraction that depends linearly on their separation. Although quantum theory is necessary to calculate from first principles the magnitude of the parameters involved, in this chapter we shall show that many optical effects can be interpreted physically in terms of this model by the use of classical mechanics. Some of the quantum-mechanical ideas behind dispersion will be discussed later in Chapter 14, but most are outside the scope of this book.
In this chapter we shall learn:
about the way in which a classical dipole atom responds to an oscillating electromagnetic field;
about Rayleigh scattering, and why sky light is blue and polarized;
how refractive index, absorption and scattering are related;
that dispersion, the dependence of refractive properties on frequency, results from atomic resonances;
about anomalous dispersion near to absorption lines;
analytical relationships between refractive index and absorption;
about plasma absorption and magneto-optical effects;
whether signals can be propagated faster than the speed of light in anomalous-dispersion regions;
a little about non-linear optical properties, which arise when the wavefields are very intense;
about harmonic generation, the photo-refractive effect and soliton propagation;
about optics at interfaces between conventional dielectrics and materials with negative permittivity;
about surface plasmon resonance.