Covariance maps of Ne for the electron kinetic energy range of 10–220 eV obtained from (a) raw experimental data; the white curve can be traced back to an additional signal associated with a reflection in the high-voltage cables of the detector appearing in the TOF spectra 320 ns away from every electron peak

<p><strong>Figure 3.</strong> Covariance maps of Ne for the electron kinetic energy range of 10–220 eV obtained from (a) raw experimental data; the white curve can be traced back to an additional signal associated with a reflection in the high-voltage cables of the detector appearing in the TOF spectra 320 ns away from every electron peak. (b) Discriminated data. (c) Energy shifted data compensating for the photon energy jitter. (d) Fourier deconvoluted data (cf figure <a href="http://iopscience.iop.org/0953-4075/46/16/164034/article#jpb470112f2" target="_blank">2</a>(b)).</p> <p><strong>Abstract</strong></p> <p>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.</p>