MULTIELECTRON EJECTION OF INNER-SHELL ELECTRONS THROUGH MULTIPHOTON EXCITATION OF CLUSTERS

The existence of coherent electronic motions induced by the presence o f 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 sp ectra of five cases studied [Kr(M), Kr(L), Xe(N), Xe(M) and Xe(L)]. An alysis shows that the multiphoton interaction can enter a regime of st rong-coupling (Z(2) alpha greater than or equal to 1) in which the rat e of multiple electron ejection can become comparable to the removal o f a single electron. The enhanced coupling arises from the coherent mo tion of the (Z) field-ionization electrons whose interactions construc tively interfere, thereby behaving like a quasi-particle with a charge Ze. This mechanism consistently explains (1) the unusually high value s of Xe M-shell ionization observed in both Xe(M) [Xe36+] and Xe(L) [X e45+] emissions and (2) the anomalous double 2p vacancy production see n in the Xe(L) spectrum. Clusters of heavy atoms appear as exceptional ly favourable systems for the copious production of multiple vacancy h ollow atom configurations.