Determination of the neon double core hole lifetime using high-intensity x-rays from the LCLS

The concentration of x-ray photons in a focussed radiation pulse at the SLAC Linac Coherent Light Source (LCLS) exposes atoms to multiple sequential photoabsorption processes [1]. For $\sim$keV x rays the absorption in neon targets primarily the 1s shell and hollow neon atoms are readily created when the rate of photoabsorption exceeds that of inner-shell decay. With typical LCLS parameters and a $\sim$1 micron focus, we observed double core-hole states in neon for up to $\sim$20\% of 1s ionization events. For comparison, electron-electron correlations lead to double-to-single core-hole ratios of just 0.3\% under single photon absorption conditions [2]. Using the high-resolution electron time-of-flight spectrometers of the LCLS AMO Physics end station, we measured the Ne {\em KK-KLL} Auger hypersatellite spectrum and determined the lifetime of the Ne$^{2+}$(1s$^{-2}$) doubly core-excited state. The results are compared to theoretical predictions. \\[4pt] [1] L. Young {\em et al.}, Nature {\bf 466}, 56 (2010). \par\noindent [2] S. H. Southworth, {\em et al.} Phys. Rev. A {\bf 67}, 062712 (2003).