ABSTRACT
In this chapter we will give a qualitative overview of the interaction of light with matter, which is necessary to understand the origin of nonlinear optical effects. A rigorous mathematical treatment is beyond the scope of this book and can be found in many standard textbooks on optics (Stratton 1941; Böttcher 1973). Instead we will focus on the basic principles underlying linear and nonlinear optics, bearing in mind the background and interest of the readers for which this book was written.
