We perform time-dependent quantum calculations on the ionization dynamics of helium in intense ultrashort laser fields. A linear model of the atom is used to extract single- and double-ionization yields for a 780 nm excitation. For an intensity of 1015 W cm-2 clear evidence is found for a direct double-ionization process which is caused by rescattering of an electron from the core in the presence of the field. A momentum-space analysis of the wavefunctions shows that in this case both electrons are preferentially emitted in the same direction and with different momenta.
|Original language||American English|
|Number of pages||10|
|Journal||Journal of Physics B: Atomic, Molecular and Optical Physics|
|State||Published - 14 Feb 2000|