Evidence for phonon hardening in laser excited gold using x-ray diffraction at a hard x-ray free electron laser

The X-ray diffraction data were collected at the LCLS using an ePix10k detector. The detector was calibrated using a CeO2 calibrant. The orientation of the detector was then determined using the open source software Dioptas. The data were then corrected for polarization (the LCLS beam was vertically polarized). The edges of each detector tile were masked. The details about the extraction of the normalized intensity is found in the Materials and Methods of the manuscript. For timing between the optical laser pulse and the X-ray pulse, we used the time tool system available at MEC. The extraction of the relative timing, determination of the absolute timing, and timing uncertainties can be found in the Materials and Methods of the manuscript.