Speaker
Description
The investigation of light-matter interaction with weakly-bound van der Waals clusters of atoms bridges the gap between the photophysics of isolated atoms and bulk materials. When exposed to intense ultrashort laser pulses, these clusters can efficiently absorb the energy, and transform into dense, short-lived plasma. This leads to the emission of energetic electrons and highly charged ions, and even X-rays and neutrons, with potential applications ranging from producing attosecond pulses via High Harmonic Generation (HHG) to triggering nuclear fusion [1]. Consequently, studying these plasma states is fundamental to uncovering the complex many-body physics of matter under extreme conditions.
We studied how these plasmas form and evolve with time in the prototype system of helium nanodroplets doped with argon atoms upon irradiation of intense infrared (IR) femtosecond pulses [2]. Ultrashort soft X-ray pulses from SwissFEL were used to further ionize the system at different time delays with respect to the IR pulses, and corresponding X-ray photoelectron spectra (XPS) were recorded using a hemispherical energy analyser at the Maloja endstation [3]. Here, for the first time, we successfully demonstrated that the recorded time resolved XPS maps can capture the evolution of Coulombic cluster potential of the IR-induced nanoplasma, which perturbs the electron binding energies of the constituents, in real time up to a few nanoseconds. Insights gained from these spectroscopic data, such as, formation of He+ and He2+ ions and their subsequent recombination with electrons inside the plasma, will be presented in detail, alongside supporting theoretical calculations. Furthermore, the time resolved XPS scheme implemented here serves as a more direct probe for characterizing the evolution of the mean-field cluster potential and the underlying ion-electron recombination dynamics during plasma expansion, in contrast to other experimental methods, such as, fluorescence measurements, time resolved- ion time of flight and Auger electron spectroscopy [4].
References:
[1] Th. Fennel et. al., Rev. Mod. Phys., 82, 2 (2010), U Saalmann et. el., J. Phys. B: At. Mol. Opt. Phys. 39 (2006) R39–R77 [2] S R Krishnan et. al., Phys. Rev. Lett. 107, 173402 (2011), S R Krishnan et. al., New Journal of Physics 14 (2012) 075016 [3] E. Prat et. al., Nature communications, 2023, 14, 5069. R. Abela et. al., Synchrotron Radiation, 2019, 26, 1073–1084 [4] S. M. Vinko et. al., Nature, 482, 59–62 (2012), M. Kelbg et. al., Phys. Rev. Lett., 125, 093202 (2020)
| Scientific Topics | AMO Physics |
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