The uploaded two sets of experimental data contain the raw TDBS signals recorded at each pressure step for the MgO [100] and [111] samples. Please note that each “.txt” file contains two columns of data, the first column is time in picosecond, the second column is the relative change of reflectivity.

The uploaded Tables “Table MgO 100” and “Table MgO 111” summarize our processed experimental data, as well as the recently measured refractive indexes and accordingly the derived longitudinal sound velocities. In which, the pressures are given in GPa, Brillouin frequencies in GHz, longitudinal sound velocities VL<100> and VL<111> in km/s. Refractive indexes are dimensionless.