Ultrafast plasma dynamics in laser-irradiated nanowire arrays probed with an X-ray free-electron laser

Nanowire arrays are excellent nanostructured target materials for high-energy density (HED) plasma studies and applications because of their enhanced energy absorption properties. However, investigations of the spatiotemporal dynamics of laser-irradiated nanowire arrays remain limited, since conventional time-resolved diagnostics such as X-ray streak cameras and flash radiography cannot readily capture the rapid plasma-state transitions within these structures. This study reports spatiotemporally resolved measurements of laser energy absorption and electron transport in laser-irradiated nanowire arrays using an X-ray free-electron laser (XFEL). Pump–probe shadowgraph measurements were performed with an XFEL, achieving a temporal resolution of 100 fs and spatial resolution of 3 µm. Instantaneous heating of the nanowire array was observed at the onset of laser irradiation, followed by a significant temperature increase due to wire collapse. The X-ray shadowgraph results confirmed that further enlargement of the heated area by laser irradiation was suppressed by the restricted electron transport in the array. These observations advance our understanding of HED plasma formation and evolution within the laser-irradiated nanowire arrays, laying a foundation for various applications that employ such arrays.