12 July 2018
Attosecond splits in atoms
Published online 26 July 2010
When light photons strike an atom, the impact knocks some electrons whizzing around the nucleus out of its flight-path, or 'atomic orbital', and beyond the atom's outer shell.
In a sense, electrons travel in distinct energy levels designated according to how far from the nucleus they orbit. Electrons leave atoms at the instant photons of sufficient energy are absorbed into the atom. Einstein first described this 'photoemission' over a century ago.
An international team, including Abdallah Azzeer from King Saud University, Saudi Arabia, fired two synchronized laser pulses at a cloud of neon gas. In a first step, x-ray laser pulses lasting only about 200 attoseconds (10-18s) are absorbed and lead to the release of electrons from the atoms. Later, visible laser pulses of 4 femtoseconds (10-15s) duration probe the emission time of the electrons.
They detected that the emission of electrons originating from the 2p orbit lagged behind electrons from the 2s orbital by 21 +/-5 as. This allowed the movement of electrons to be timed within billionths of a billionth of a second, or attoseconds (as) resolution, a 10-fold improvement compared to earlier experiments.
Detailing electron emission with attosecond precision should help physicists to fine tune theoretical models of the atom and better predict how electrons interact with each other in metals or semiconductors.