ABSTRACT
This chapter presents the theory of light wave propagation in linear and weakly nonlinear dielectrics. It introduces the effects of delay, the noninstantaneous response of the induced polarization to the applied electric field, and shows how it gives rise to a frequency-dependent refractive index. The chapter discusses the elementary plane wave or wavetrain solutions of Maxwell's equations, the building blocks of more general solutions, and introduces the notions of phase, wavevector, frequency, and dispersion relation, which connects the latter two. It also discusses the nature of the relations between the components of the susceptibility tensors when the polarization is expressed as a power series in the electric field. The chapter shows that an intensity-dependent refractive index of a wavetrain gives rise to a nonlinear dispersion relation involving the field intensity in addition to the wavevector and frequency. It reviews the main ideas of geometric optics, in which a plane wave travels in a medium of slowly varying refractive index.
