Damage threshold in pre-heated optical materials exposed to intense X-rays

Abstract

Materials exposed to ultrashort intense x-ray irradiation experience various damaging conditions depending on the irradiation temperature. A pre-heated target exposed to intense x-rays plays a crucial role in numerous physical-technical systems, ranging from the heavily and repeatedly radiation-loaded optics at x-ray free-electron laser facilities to the inner-most wall of prospective inertial fusion reactors. We study the temperature dependence of damage thresholds in different classes of materials theoretically: an insulator (diamond), a semiconductor (silicon), a metal (tungsten), and an organic polymer (PMMA). The numerical techniques used here enable us to trace the evolution of both the electronic state and the atomic dynamics of the materials. It includes damage mechanisms such as thermal damage, induced by an increased irradiation temperature due to energy transfer from x-ray-excited electrons, and nonthermal phase transitions, induced by rapid interatomic potential changes due to the excitation of electrons. We demonstrate that in the pre-heated materials, the thermal damage threshold tends to stay the same or lowers with the increase of the irradiation temperature, whereas nonthermal damage thresholds may be lowered or raised, depending on the particular material and specifics of the damage kinetics.