Multi-photon processes in Ne and associated electron kinetic energies
Figure 1. Multi-photon processes in Ne and associated electron kinetic energies. The left-hand diagram shows the kinetic energies of electrons created upon ionization by 1062 eV photons, labelled according to the chronological sequence of the following processes: core photoionization (P), valence photoionization (V), single-photon core-valence double ionization (D) and Auger decay (A). Four crucial multi-photon processes are schematically presented in the right-hand diagram using the same notation. Arrows indicate the ejected electrons and are numbered in chronological order.
We report on a detailed investigation into the electron emission processes of Ne atoms exposed to intense femtosecond x-ray pulses, provided by the Linac Coherent Light Source Free Electron Laser (FEL) at Stanford. The covariance mapping technique is applied to analyse the data, and the capability of this approach to disentangle both linear and nonlinear correlation features which may be hidden on coincidence maps of the same data set is demonstrated. Different correction techniques which enable improvements on the quality of the spectral features extracted from the covariance maps are explored. Finally, a method for deriving characteristics of the x-ray FEL pulses based on covariance mapping in combination with model simulations is presented.