When light pulses from an extremely powerful laser system are fired onto material samples, the electric field of the light rips the electrons off the atomic nuclei. For fractions of a second, a plasma is created. The electrons couple with the laser light in the process, thereby reaching nearly the speed of light. When flying out of the material sample, they pull the atomic cores (ions) behind them. In order to investigate this complex acceleration process experimentally, researchers from the German research center Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have developed a novel type of diagnostics for innovative laser-based particle accelerators. Their results are now published in the journal Physical Review X.