1. L. P. Rappoport, B. A. Zon, and N. L. Manakov, Theory of Atomic Multiphoton Processes [in Russian], Atomizdat, Moscow (1978).
2. N. B. Delone and V. P. Krainov, Atoms in Strong Radiation Fields [in Russian], Énergoatomizdat, Moscow (1984).
3. N. B. Delone, V. P. Krainov, and D. L. Shepelyanskii, Usp. Fiz. Nauk,40, No. 3, 355 (1983).
4. A. I. Baz', Ya. B. Zel'dovich, and A. M. Perelomov, Scattering, Reactions and Decay in Nonrelativistic Quantum Mechanics [in Russian], Nauka, Moscow (1971).
5. J. L. Levine and T. M. Sanders, Phys. Rev.,154, No. 1, 138 (1967).