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Physicists Measure Atomic Event Within a Trillionth of a Billionth of a Second

New method captures photoemission of electrons from helium atoms with a degree of precision impossible with cameras.
Image: M. Ossiander (TUM) / M. Schultz (MPQ)

Way back in 1905, Albert Einstein described a process he called the photoelectric effect (or photoemission), in which electrons get knocked out of the atoms that held them after being struck by light. It's a seemingly instantaneous process, and for years we've only been able to observe and study its aftereffects.

That's no longer the case. Recently, German physicists at LMU Munich and the Max Planck Institute of Quantum Optics (MPQ) measured the time it took for one of the two electrons in a helium atom to leave the atom after it interacted with light. By using lasers, they discovered that they could correctly measure such an event at a rate of up to 850 zeptoseconds, a measure of time equaling a trillionth of a billionth of a second.

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Specifically, the span of time from when a photon hits the two electrons to the moment when one electron ejects is somewhere in the neighborhood of 5 to 15 attoseconds, with an attosecond being one quintillionth of a second. Never before has an internal atomic event been measured so accurately. It's so precise, it's said to be the shortest event ever measured.

No camera can capture events this quickly. Instead, the physicists shot a ultraviolet light pulse at a helium atom for one attosecond, and then simultaneously shot an infrared laser pulse at the same spot for four femtoseconds (a femtosecond being one quadrillionth of a second). The infrared pulse, lasting longer, then detected the departing electron. From there it was possible to look at the electromagnetic field from the infrared laser pulse and determine if the electron had accelerated or decelerated. The process also allowed the researchers to tell if one of the electrons had absorbed part of the photon's energy or all of it.

Not only is it a tremendous achievement, but it also grants a clearer picture of how exactly atoms work and thereby opens a means of testing atomic theories through experimentation. The researchers published their findings in the journal

Nature

earlier this month.