Free‐electron laser pulse‐based X‐ray absorption spectroscopy measurements on warm dense copper are presented. The incident X‐ray pulse energies were measured with a detector assembly consisting of a photocathode membrane and microchannel plates, and the transmitted energies were measured simultaneously with a photodiode detector. The precision of the absorption measurements was evaluated. For a warm dense copper foil irradiated by an intense femtosecond laser pulse, the enhanced X‐ray absorption below the L₃‐edge, followed by the rapid evolution of highly excited Fermi liquid within a picosecond, were successfully measured. This result demonstrates a unique capability to study femtosecond non‐equilibrium electron–hole dynamics in extreme states of matter.

中文翻译：

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PAL-XFEL上的热致密物质的飞秒软X射线吸收光谱

提出了基于电子的基于激光脉冲的X射线吸收光谱法对稠密铜的测量。使用由光电阴极膜和微通道板组成的检测器组件测量入射的X射线脉冲能量，并使用光电二极管检测器同时测量透射的能量。评估吸收测量的精度。对于强烈的飞秒激光脉冲照射的温暖致密的铜箔，成功地测量了在L ₃边缘以下增强的X射线吸收，然后在皮秒内快速激发了高激发费米液体。该结果证明了在极端物质状态下研究飞秒非平衡电子-空穴动力学的独特能力。