X-ray free electron laser heating of water and gold at high static pressure

Probing of reactive materials such as H₂O ices and fluids at the high pressures and temperatures of planetary interiors is limited by unwanted chemical reactions and confinement failure. Faster experiments can mitigate such issues, but the common approach of adiabatic compression limits the conditions achieved. This study demonstrates a fast experimental strategy for the creation and probing of selected extreme states using static compression coupled with ultrafast X-ray laser heating. Indirect X-ray heating of H₂O through the use of a gold absorber is evidenced by sample melting inferred from textural changes in the H₂O diffraction lines and inter-dispersion of gold and H₂O melts. Coupled with numerical analysis of femtosecond energy absorption, thermal equilibration, and heat transfer, all evidence indicates that temperatures in excess of an electron volt have been reached in the H₂O at high pressure. Even after repeated heating, samples stayed chemically unchanged from the starting material.