New technique traces ejected electrons back to atomic shells

In a detailed study of how intense light strips electrons from atoms, researchers used an X-ray laser, SLAC’s Linac Coherent Light Source (LCLS), to measure and sort the ejected electrons and discover how this process takes place.

The results give scientists a clearer picture of how ultrabright X-ray light creates highly charged states of matter and how X-rays can damage samples under study, which could prove useful in interpreting data for a range of LCLS experiments.

The X-ray pulses at LCLS are so intense that they can send multiple particles of light, called photons, into the same atom, simultaneously or sequentially ejecting many electrons from the same atom and causing a reshuffling of the remaining electrons. Since electrons carry a negative charge, the atom becomes more positively charged as they are stripped away.

In one of the earliest LCLS experiments, conducted in 2009, researchers explored this electron-stripping process in neon atoms by measuring the final charge state of the atoms. Now, in an experiment described in Physical Review Letters, researchers used a new technique to gain more insights about the stripping process.

They mapped out the energy signatures of many of the electrons punched out of the atoms by the ultrabright X-ray light, and used a sophisticated algorithm to identify electrons associated with the same atom. The results also revealed details of competing pathways for this stripping process.

This “energy map” shows the energy signatures of electrons associated with neon atoms studied at SLAC’s Linac Coherent Light Source X-ray laser. At left are electron energy signatures associated with “hollow” neon atoms, whose inner electrons have been ejected from the atoms. At right are energy signatures associated with removal of both an outer-shell and inner-shell electron. Credit: L.J. Frasinski, et al.

The research was made possible by a custom-built 2-meter-long instrument, called a magnetic bottle spectrometer, that measures the energies of most of the escaping electrons. A complex statistical technique sorts the electrons into “bins” based on their energies, compares those energies and accounts for inherent energy fluctuations, or jitter, in LCLS pulses. More here New technique traces ejected electrons back to atomic shells.

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