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2. See papers inMultiphoton Ionization of Atoms, ed. by S.L. Chin and P. Lambropulos also in Atoms in Intense Laser Fields, ed. by M. Gavrila (Academic Press, New York, 1992) Academic Press, New York 1984).
3. G. Petite, J. Morrelec, D. Normand: J. Physique40,115 (1979)
4. P. Agostini, F. Fabre, G. Mainfray, G. Petite, N.K. Rahman: Phys. Rev. Lett.42, 1127 (1979)
5. P. Kruit, J. Kimman, H.G. Muller, M.J. van de Wiel: Phys. Rev. A28, 248 (1983).