
172 Light–Matter Interaction
there will be at least two differential equations of the form Eq. (3.93), with a
third-order susceptibility, corresponding to the fundamental and third harmonic
fields. More equations have to be added if more frequencies are generated.
It is beyond the scope of the book to give a detailed description of the
various possible nonlinear effects and excitation schemes. The reader is referred
to the standard texts on nonlinear optics, for example Schubert and Wilhelmi [2],
Boyd [8], Bloembergen [9], and Shen [11]. Here we shall restrict ourselves to
a nonlinearity of second order that is responsible for second harmonic genera- ...