Multiphoton processes in helium: Ab-initio time-dependent studies |
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| Lampros Nikolopoulos | |
| The Queen's University of Belfast | |
| Helium has received much of the theoretical attention, as it is the most amenable to ab-initio and accurate calculations. On the other hand, the first experimental results of multiphoton absorption of helium, have obtained years ago with conventional (long-wavelength) laser sources while further experimental studies with radiation from high-harmonic generation (HHG of Ti:Sapphire) or free-electron laser (FLASH) sources have also recently reported.
Motivated mainly by the problem of direct versus sequential two-electron double ionization under strong lasers of short duration, much attention has focused in the last few years on two-photon double ionization (TPDI) in two-valence electron atoms. In addition, it is of highly experimental interest the calculation of absolute harmonic yields of Helium when irradiated by a strong laser In this work we present an ab-initio time-dependent approach, capable of providing in the same calculation, ionization yields, photo-electron energy and angular distributions. The transition amplitudes in the interaction of helium with the light, are calculated through an approach relying on basis sets constructed in terms of B-splines that has been developed over the years with the objective of time-dependent calculations, and has been employed in that context. |