The development of short-pulse lasers has been instrumental in bypassing the intermediate destabilizing events that occur during superheating and has allowed experiments to approach the entropy catastrophe threshold4,5,6. 

Experiments using heating rates exceeding 1014 K s–1 have achieved superheating within the range of T ≈ 1.4Tm – 2.1Tm, where Tm is the melting temperature, nearing but not fully reaching the anticipated limit7,8,9,10,11. 

Notwithstanding the advancements in heating rates, a direct, model-independent method for accurately measuring ion temperatures in hot, solid-density systems has remained elusive, which constitutes a major roadblock to drawing precise and reliable conclusions about superheating. 

Indeed, earlier methodologies often relied on indirect measures of ion temperature through analysis of material structure or energy absorption12.

In response to this challenge, we utilize inelastic X-ray scattering in the backscattering regime to directly ascertain ion velocity distributions and thus determine the ion temperatures.

Leveraging this pioneering technique, we show that gold subjected to short-pulse laser irradiation unambiguously reaches heating rates exceeding 1015 K s–1, propelling the ions to temperatures of T ≈ 14Tm without losing the solid structure. 

Source: Nature