Abstract
We report a time-resolved study of the relaxation dynamics of Al films excited by ultrashort intense free-electron laser (FEL) extreme ultraviolet pulses. The system response was measured through a pump-probe detection scheme, in which an intense FEL pulse tuned around the Al L2,3 edge (72.5 eV) acted as the pump, while a time-delayed ultrafast pulse probed the near-infrared (NIR) reflectivity of the Al film. Remarkably, following the intense FEL excitation, the reflectivity of the film exhibited no detectable variation for hundreds of femtoseconds. Following this latency time, sizable reflectivity changes were observed. Exploiting recent theoretical calculations of the EUV-excited electron dynamics [N. Medvedev et al., Phys. Rev. Lett. 107, 165003 (2011)], the delayed NIR-reflectivity evolution is interpreted invoking the formation of very-long-living nonthermal hot electron distributions in Al after exposure to EUV pulses. Our data represent the first evidence in the time domain of such an intriguing behavior.
Highlights
The interaction of intense ultrashort extreme ultraviolet (EUV) radiation with solid matter is currently a topic of great interest in physics, as it can generate exotic states of matter, such as dense plasmas and warm dense matter (WDM) [1,2,3,4,5]
We report a time-resolved study of the relaxation dynamics of Al films excited by ultrashort intense free-electron laser (FEL) extreme ultraviolet pulses
The system response was measured through a pump-probe detection scheme, in which an intense FEL pulse tuned around the Al L2,3 edge (72.5 eV) acted as the pump, while a time-delayed ultrafast pulse probed the near-infrared (NIR) reflectivity of the Al film
Summary
The interaction of intense ultrashort extreme ultraviolet (EUV) radiation with solid matter is currently a topic of great interest in physics, as it can generate exotic states of matter, such as dense plasmas and warm dense matter (WDM) [1,2,3,4,5]. We report a time-resolved study of the relaxation dynamics of Al films excited by ultrashort intense free-electron laser (FEL) extreme ultraviolet pulses.
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