Multi-electron ejection of inner-shell electrons through multiphoton excitation of clusters

Abstract

The existence of coherent electronic motions induced by the presence of a strong external optical field enables the process of direct multi-electron ejection from an inner-shell to occur with high probability. Experimental evidence for this mechanism is present in the observed spectra of five cases studied (Kr(M), Kr(L), Xe(N), Xe(M) and Xe(L)). Analysis shows that the multiphoton interaction can enter a regime of strong-coupling (Z2a>or=1) in which the rate of multiple electron ejection can become comparable to the removal of a single electron. The enhanced coupling arises from the coherent motion of the (Z) field-ionization electrons whose interactions constructively interfere, thereby behaving like a quasi-particle with a charge Ze. This mechanism consistently explains (1) the unusually high values of Xe M-shell ionization observed in both Xe(M) (Xe36+) and Xe(L) (Xe45+) emissions and (2) the anomalous double 2p vacancy production seen in the Xe(L) spectrum. Clusters of heavy atoms appear as exceptionally favourable systems for the copious production of multiple vacancy hollow atom configurations.