Adaptation of the modified adiabatic approximation to strong-field ionization

Savichev\u2019s modified adiabatic approximation [Sov. Phys. JETP 73, 803 (1991)] is used to obtain a general form of a quantum-mechanical amplitude of ionization by a low-frequency laser field. The method possesses only one requirement that the frequency of the laser field must be low. Connections of the obtained result with the quasiclassical approximation and other previous investigations are discussed.Peer reviewed: YesNRC publication: Ye