Electrons move on the time scale of attoseconds, each of which is a vanishingly short billionth of a billionth of a second. With ultrafast pulses of light, researchers have measured the photoemission of electrons from their valence shells, a process that was once considered instantaneous. For developing the tabletop laser systems necessary to glimpse such electron dynamics, three researchers were awarded the 2023 Nobel Prize in Physics (see Physics Today, December 2023, page 13).
Now Stanford University’s Taran Driver, Agostino Marinelli, and James Cryan and their colleagues have harnessed recent advances in x-ray free-electron lasers (XFELs) to witness the photoelectric effect in the electrons closest to an atom’s nucleus. Complex, multielectron interactions can be studied with measurements of core electrons, but the energies of such electrons had been out of reach for attosecond pulses of light produced with low-energy tabletop lasers.
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