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Figure 1
(a) An XFEL X-ray pulse is used to collect a diffraction pattern from a gold thin film after it has been pumped by an optical laser pulse. This pattern is collected in one shot on a Rayonix optically coupled charge-coupled device (CCD) 50 mm behind the sample. As the laser destroys the sample, each shot is taken using a unique sample window from a 2D array. (b) Diffraction intensity (log scale) from single pump–probe shots of monochromatic X-rays from PAL-XFEL with varying pump–probe delay times. The background has been measured and subtracted. Dashed lines indicate split Bragg peak positions after pumping. (c) Schematic of melting around grain boundary locations in a polycrystalline metal thin film, indicating the propagation of the laser-excited melt front as described by Assefa et al. (2020BB1). (d) 1D spatial temperature distribution 20 ps after a spike of melt is generated at a grain boundary. The heat conducts into the grain with a melt-front velocity proportional to the heat flux, as proposed by Assefa et al. (2020BB1). The temperature is fixed in the region where the metal is actively melting due to latent heat, resulting in a block of melting material sandwiched between two melt fronts moving at different velocities.

IUCrJ
Volume 10| Part 6| November 2023| Pages 656-661
ISSN: 2052-2525
https://doi.org/10.1107/S2052252523009363