Femtosecond x-ray diffraction can discern nonthermal from thermal melting

We theoretically investigate which experimental observations enable discrimination between thermal and nonthermal melting in femtosecond laser pulse-irradiated semiconductors. We identify that coherent phonon excitation, visible in the oscillations of various diffraction peaks, provides an opportunity to observe ongoing modifications of interatomic potential. Decoupling the effects of anharmonicity, caused by thermal heating, from the effects of evolution of the interatomic potential, due to electronic excitation, potentially enables differentiation between the two damage channels.