Abstract

In the phenomenon of laser-induced continuum structure (LICS) [1], a strong laser field embeds a discrete state structure in an otherwise unstructured continuum of states and thereby strongly modifies the ionization properties of the atom due to a probe laser. If the embedding laser is sufficiently strong and the probe laser weak, a Fano-type ionization profile is expected and coherent population trapping is possible [1]. In this paper, we investigate LICS in atomic Helium. We compare our results with the recent experimental and theoretical results of Halfmann et al [2]. In this experiment, a Nd:YAG laser was used to strongly couple the 1s4s ¹S Rydberg state with the continuum and the resulting modification of the 1s2s ¹S photo-ionization spectrum was measured. We present the results of ab initio, non-perturbative, R-matrix-Floquet calculations as well as those obtained from simple, effective two-level models that are widely used for the description of the LICS process [1]. Our findings are in good quantitative agreement with the available results of the experiment of Halfmann et al [2] and further understanding of the involved physical mechanisms is gained through our study.

© 1998 IEEE