Intensity dependence of the multiphoton-induced Xe(L) spectrum produced by subpicosecond 248 nm excitation of Xe clusters

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Abstract
Examination of the intensity dependence in the range of the multiphoton-induced Xe(L) spectrum from Xe clusters has demonstrated (i) a very high sensitivity for the production of ions having multiple vacancies and and (ii) a reduction of the average charge state of the emitting ions over the range of intensities in which the multiple-vacancy excitations are diminished. These results give evidence for a dynamical enhancement of the coupling strength arising from ordered many-electron motions induced by the incident 248 nm wave and indicate that the enhanced interaction can lead to a regime of strong coupling in which multiple electron ejection from inner shells can occur with substantial probability. Furthermore, the results are found to be in agreement with previous analyses of multiple electron processes, which involved comparisons with experimental data stemming from both electron (EBIT) and ion - atom collisional studies. The specific comparison with known properties of ion - atom ( + Ne) charge exchange collisions indicates that the multi-electron channels can dominate the multiphoton interaction if a threshold intensity is exceeded. The experimental results give evidence that this threshold falls in the 0.4 - range at 248 nm for the production of 2p vacancies in Xe clusters. These findings provide an experimental basis for the general expectation that a strengthened multi-electron coupling will govern the production of ions with deeply bound (>10 - 20 keV) multiple-vacancy states in clusters of heavy atoms irradiated at 248 nm with intensities above .
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