1. N. Bloembergen, Nonlinear Optics (Benjamin Inc., New York, Amsterdam, 1965).
2. Y.R. Shen, The Principles of Nonlinear Optics (Wiley & Sons, New York, 1984).
3. R. M. Macfarlane, this volume.
4. G. Baldacchini, this volume.
5. A. Miller, D.A.B. Miller and S.D. Smith, Adv. in Phys. 30, 697 (1981).