Measuring hot electron distributions in intense laser interaction with dense matter

Retrieving the characteristics of hot electrons produced in the interaction between solid targets and ultra-intense (I > 1018 W cm-2) laser pulses is essential for achieving progress in our understanding of the interaction physics, which is key for optimizing numerous downstream applications. Until now, various methods have been used, direct or indirect, but no correlation and no assessment of their respective merits were performed. Here we compare results retrieved from four different diagnostics, direct or indirect, as well as local or non-local, i.e. spectrometry of electrons, spectrometry of the protons accelerated by the electrons and optical probing of these beams expanding into vacuum from the targets. We show that measurements obtained locally at the target rear surface are consistent with those far away from the target and that one can use the diagnostics of the co-moving proton beams to retrieve information about electrons. (paper)