Transition from non-sequential to sequential double ionisation in   many-electron systems
  Obtaining a detailed understanding of strong-field double ionisation of many-electron systems (heavy atoms and molecules) remains a challenging task. By comparing experimental and theoretical results in the mid-IR regime, we have unambiguously identified the transition from non-sequential (e,2e) to sequential double ionisation in Xe and shown that it occurs at an intensity below $10^{14}$ Wcm$^{-2}$. In addition, our data demonstrate that ionisation from the Xe 5s orbital is decisive at low intensities. Moreover, using the acetylene molecule, we propose how sequential double ionisation in the mid-IR can be used to study molecular dynamics and fragmentation on unprecedented few-femtosecond timescales. 
Michael G. Pullen, Benjamin Wolter, Xu Wang, Xiao-Min Tong, Michele   Sclafani, Matthias Baudisch, Hugo Pires, Claus Dieter ...
physics.atom-ph