P. Lambropoulos

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).