WAVEPACKET SPREADING AND ELECTRON LOCALIZATION IN STRONG-FIELD IONIZATION

We present an analytical model of strong-field photoionization by a short-pulse laser of an electron bound in a short-range potential. We confirm its predictions by numerical evaluation of the electron's space- and time-dependent wavefunction. We show that wavepacket spreading alone makes an important contribution to the photoionization process for times shorter than a specific critical time T* that is directly proportional to the electric field strength of the laser. We refer to this regime as the spreading regime. We find that stabilization occurs for sufficiently strong fields, and that the characteristics of stabilization can also be observed in the spatial distribution of the final wavefunction as well as in the time-dependent ground state probability. Second, by studying the detailed nature of the electron wavefunction during both abrupt and non-abrupt switching-off of the laser pulse, we have identified a function that can be conveniently evaluated during a laser pulse, but which accurately provides the value of bound state probability at the end of a smooth switch-off.