TWO- AND THREE-ELECTRON ATOMS DRIVEN BY LASER FIELDS
I discuss recent developments on the theory of double photoionization of Helium
in the few-photon regime. The method is based on the expansion of the
wavefunction in terms of eigenstates of the bare atom constructed as linear
combinations of B-splines. Techniques based on a radial box with a fixed
boundary or alternatively a free boundary need to be and are employed;
especially in the case of several coupled open channels. The results pertain to
the photoelectron energy spectrum and angular distributions for two-photon
double ionization. In addition the non-perturbative solution of the
time-dependent Schrödinger equation is implemented in terms of the same
method. Signatures of direct double ionization, especially for XUV photons are
identified. Finally, ongoing work and results on the exploration of the effects
of laser coupling between triply excited hollow states of Lithium, based on
similar techniques, are also discussed.
P. Lambropoulos, P. Maragakis and J. Zhang, Physics Reports 305, 203 (1998).
L.A.A. Nikolopoulos and P. Lambropoulos, Physical Review Letters 85, 42 (2000);
also Physical Review A (in press, Dec. 2000).