Fig. 3: Ion temperature evolution.

a,b, The measured ion temperature of a gold foil, shown by symbols with error bars, after irradiation with a laser fluence of 1.9 ± 0.5 J cm⁻² (a) and 4.9 ± 0.5 J cm⁻² (b). Error bars for the broadening are derived through a bootstrap resampling method (see Methods for details). These fluences result in heating rates of 3.5 × 10¹⁵ K s⁻¹ and 6 × 10¹⁵ K s⁻¹, respectively (dashed line). Overlaid are the intensities of the (111) and (220) diffraction peaks whose disappearance can be used to identify the time of melting. Higher intensity is shown in blue. The white arrows indicate the highest temperature at which diffraction lines from a solid are observed. In both cases, the temperature of the superheated solid greatly exceeds the previously proposed limit of three times the melting temperature, shown by the horizontal dashed line.