Starring In Ultra-Short Films, Electrons Captured In Motion

Scientists hope seeing how an individual electron rides on a light wave after just having been detached from its atom will help them decipher other atomic and sub-atomic objects.
Using a stroboscopic layer that emits pulses of light at previously unheard-of rates, a team of scientists has produced the first "movie" of an individual electron "riding" on a light wave after just having been detached from its atom.

The images, the first of their kind, clearly show how electrons -- the lightest known particles possessing an electric charge -- scatter off their atoms in the process known as ionization.

In order to capture these quantum events, scientists at the Lund University Faculty of Engineering in Sweden used a laser pulsing at extremely high rates that match the incredibly fleeting life of the free electron. The ultrashort light pulses are just three hundred "attoseconds" long. It takes about 150 attoseconds for an electron to circle the nucleus of an atom, according to John Mauritsson, an assistant professor in atomic physics at Lund and one of seven researchers in the study. An attosecond is 10 to the negative 18 seconds long. "An attosecond is related to a second as a second is related to the age of the universe," explains Mauritsson in a statement.

The principle is the same as a strobe used to make conventional photographs of extremely rapid movements -- like a strobe light flashed at the same frequency as the beating wings of a hummingbird. The physicists used a new technology that generates very rapid pulses of intense laser light -- "attosecond pulses." The pulses are synchronized with an oscillating laser field that repeatedly ionizes a cloud of helium atoms.

Attosecond pulses have been attainable for a couple of years, but they were considered too weak for use in filming electrons in motion. The Lund scientists used repeated "movies" overlaid, like a photographer creating a single image from multiple exposures.

"By taking several pictures of exactly the same moment in the process, it's possible to create stronger, but still sharp, images," said Mauritsson.

The article on the experiment, "Coherent Electron Scattering Captured by an Attosecond Quantum Stroboscope" appears in the current issue of Physical Review Letters. The slow-motion video of the scattering electron -- which actually shows the energy distribution of the electron -- shows an expanding, multicolored bull's-eye pattern.

The scientists hope to use the stroboscopic laser technique to study how electrons interact with other atomic and sub-atomic objects.

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