ABSTRACT
Lasers provide highly coherent optical waves having strong electromagnetic field amplitude. At sufficiently high level of their field / intensity, the response of the medium during its interaction with the lasers does not remain linear, but it shows nonlinear dependence on the electric field strength. This forms the basis of nonlinear optics and led to the discovery of two-photon absorption (2PA), saturable absorption (SA), reverse saturable absorption (RSA), nonlinear refraction (NLR), second and third-harmonic generations, sum and difference frequency generations, degenerate four-wave mixing (DFWM), and so forth. In this chapter, these nonlinear phenomena are discussed in detail. Special emphasis is given to the second-and the third-harmonic generations.
