**Table 1.** Location of the correlation islands deduced from figure 2. Their assignments are confirmed by comparison with theoretical predictions. The *E*_{kin} values given correspond to specific sequences of the multi-ionization processes as labelled in bold in the third column. To denote the Ne 1s^{r}2s^{t}2p^{k} electron configurations, the notation *rtk* is used.

**Abstract**

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.