1. A. Zavriyev, P. H. Bucksbaum, H. G. Muller, and D. W. Schumacher, Phys. Rev. A 42, 5500 (1990).
2. D. Normand, S. Dobosz, M. Lezius, P. D’Oliveira, and M. Schmidt, in Multiphoton Processes 1996, P. Lambropoulos and H. Walther (eds.), IOP, Bristol (1997), p. 287.
3. V. P. Makarov and M. V. Fedorov, Zh. Éksp. Teor. Fiz. 70, 1185 (1976) [Sov. Phys. JETP 43, 615 (1976)].
4. M. V Fedorov, Zh. Éksp. Teor. Fiz. 73, 134 (1977) [Sov. Phys. JETP 46, 69 (1977)].
5. A. D. Bandrauk and G. Turcott, J. Phys. Chem. 87, 5098 (1983).