Generalization of the Keldysh Theory of Above-Threshold Ionization for the Case of Femtosecond Pulses.

摘要

We develop a theory of the Keldysh-type appropriate for femtosecond excitation of atomic hydrogen. The new theory is tested by comparison with results of a direct numerical integration of the three-dimensional Schrodinger equation. In the case studied it is found that several of the standard approximations used in Keldysh calculations and in Fermi golden rule calculations are not valid. In particular, the slowly varying population approximation is not valid, and inhibition of ionization by coherent population trapping can occur. Reprints. (rrh)