1. For recent reviews of strong-field researches, see, for example, Atoms in Intense Laser Fields, Adv. At. Mol. Opt. Phys. Sup. 1, edited by M. Gavrila (Academic Press 1992).
2. See, for example, P.K. Aravind and J.O. Hirschfelder, J. Phys. Chem. 88 (1984) 4788.
3. J.H. Shirley, Phys. Rev. 138 (1965) B979.
4. G. Floquet, Ann. l’Ecol. Norm Sup. 12 (1883) 47; J. H. Poincar, Les Méthodes Nouvelles de la Mechanique Celeste, Vols. I, II, IV, (Paris, 1892, 1893, 1899).
5. For review of Floquet methods for two-level systems, see, D.R. Dion and J.O. Hirschfelder, Adv. Chem. Phys. 35 (1976) 265.