1. 1. For review, see articles in "Multiphoton Processes" edited by G. Mainfra) and P. Agostini (CEA Press, Paris, 1991)
2. 2. in "Atoms in Intense Laser Fields", edited by M Gavrila (Academic, Orlando, 1992)
3. 3. in "Super-Intense Laser Physics", ed. by B. Piraux, A. L'Huillier and K. Rzazewski, NATO ASI Series Vol. 316 (Plenum Press, Amsterdam, 1993)
4. 4. and in "Multiphoton Processes", ed. by D.K. Evans and S.L. Chin, Series in Optics and Photonics Vol. 6 (World Scientific, 1994).
5. J.H. Eberly and R. Grobe, in “Super-Intense Laser Physics”, Ref. 1. p. 445.