Fig. 1: Sample configuration and diagnostics used for X-ray heating of H2O at ~67 GPa.
a Photomicrograph showing the three doughnut-type couplers (Au, Cu, and Ag) in DAC 8, which were used to indirectly heat the H2O sample during XFEL irradiation. The couplers were imbedded in the Re gasket and insulated from the diamond anvils by a thin layer of H2O, as illustrated in (b) and (c). Data were collected with the XFEL beam (<8 µm FWHM) aligned to the center of the coupler hole so that the coupler was heated by the tails of the beam. d–f Data from run 533, which was collected from the Cu coupler using 70% X-ray transmission. d Pulse energy as a function of time for the 300 pulses in the train. e SOP spectrogram after fluorescence removal showing the thermal emission from the coupler during the run, where time 0 corresponds to the arrival of the first XFEL pulse. f Temporal evolution of the total SOP intensity and temperature determined from a Planck fit to the thermal emission in a 9.07 µs time window, where the horizontal error bars indicate the bin width and the vertical error bars correspond to one half of the standard deviation confidence from the Planck fit. The temporal resolution of the SOP is not sufficient to resolve temperature oscillations during the heating/cooling process (Fig. 2a); instead, it is sensitive to the hottest part of the run where thermal emittance is the brightest. Source data for panels (d)–(f) are provided as a Source Data file.
