Smallest sliver of time yet measured sees electrons fleeing atom...
Adam Rifkin stashed this in Time
It’s like catching light in action.
For the first time, physicists have measured changes in an atom to the level of zeptoseconds, or trillionths of a billionth of a second – the smallest division of time yet observed.
In this case, the speed demon was an electron escaping the bonds of its parent atom. When light strikes electrons, they get excited and can break free from their atoms. The photon’s energy is either entirely consumed by one electron or divided among several. This electron ejection is known as the photoelectric effect, and was described by Albert Einstein in 1905.
Previous experiments studying this effect could only measure what happened after the electron was kicked out of an atom, says Martin Schultze at the Max Planck Institute of Quantum Optics in Garching, Germany.
Now, he and his colleagues have seen the other end of the process. They measured the entire ejection of electrons from a helium atom from start to finish with zeptosecond precision (10-21 seconds), marking the smallest time slot ever measured.
In a series of experiments, the team fired an unspeakably brief, extremely ultraviolet laser pulse at a helium atom to start exciting its pair of electrons. This pulse lasted just 100 to 200 attoseconds, or 10-18 seconds. But by making many readings and calculating their statistical spread, they were able to measure events at a rate of 850 zeptoseconds.
They also fired a near-infrared laser pulse, lasting just four femtoseconds (1 femtosecond is 10-15 seconds). This pulse was able to detect an escaping electron as soon as it was freed from the helium atom. Depending on the electromagnetic field of the laser pulse, the electron either accelerated or decelerated.
“Using this information, we can measure the time it takes the electron to change its quantum state from the very constricted, bound state around the atom to the free state,” says Marcus Ossiander at the Max Planck Institute.
The ejections took between 7 and 20 attoseconds, according to Schultze, depending on how the electron interacted with the nucleus and the other electron.