1. V. S. Letokhov and V. P. Chebotaev, Ultrahigh-Resolution Nonlinear Laser Spectroscopy (Nauka, Moscow, 1990) [in Russian].
2. S. G. Rautian, G. I. Smirnov, and A. M. Shalagin, Nonlinear Resonances in the Spectra of Atoms and Molecules (Nauka, Novosibirsk, 1979) [in Russian].
3. Nonlinear Spectroscopy, Ed. by N. Bloembergen (Societa Italiana di Fisica, Bologna, Italy, 1977; Mir, Moscow, 1979).
4. A. K. Popov, Introduction to Nonlinear Spectroscopy (Nauka, Novosibirsk, 1983) [in Russian].
5. S. Stenholm, Foundations of Laser Spectroscopy (Wiley, New York, 1984; Mir, Moscow, 1987).