Time-dependent effects in the nonsequential ionization of helium at various wavelengths

Calculations of the double ionization of a model 1D helium atom interacting with an intense short laser pulse are presented. A substantial signature of nonsequential double ionization is found for all the wavelengths that are considered, from 248 nm to 1064 nm, provided that sufficiently short pulses are employed. We show how one can modify the size of the “knee” structure of the double ionization yield curve by varying the laser pulse duration. The underlying mechanism of the correlated double electron ejection is investigated and discussed.