Ultrafast probe using femtosecond electron pulses: real-time probing plasma dynamics

In recent years, femtosecond electron pulses have emerged as a powerful tool to probe ultrafast dynamics in matter. They have been used in ultrafast diffraction and imaging to reveal the atomic-detail structural dynamics in real time, covering a wide range of applications in physics, materials science, chemistry and biology. In this study, we report direct and real-time measurements of the ejected-charge dynamics surrounding laser-produced warm dense matter using femtosecond electron pulses. Our study reveals a two-step dynamical process of ejected electrons: an initial emission and accumulation of electrons outside the pumped surface followed by the formation of escaping hemispherical clouds of electrons into the vacuum at an isotropic and nearly constant velocity. Based on these observations, we also developed a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud. The perspective of the field is also reviewed.

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