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How to Use a Laser to Kick an Electron out of a Molecule

Accepted submission by Anonymous Coward at 2022-11-19 19:24:02
Science []

For all its possibilities, nature tends to replay one particular scene over and over again: the confrontation between matter and light.

But physicists still don't know the details of what happens when photons meet atoms and molecules. The play-by-play occurs over attoseconds, which are quintillionths of a second (or 10-18 of a second). It takes a special laser that fires attoseconds-long pulses to study such ephemeral phenomena. You can think of the length of a laser pulse a bit like the shutter speed of a camera. The shorter the pulse, the more clearly you can capture an electron in motion. By studying these moments, physicists gain more understanding of a fundamental process ubiquitous in nature.

Last month, physicists at multiple academic institutions in China published results in Physical Review Letters showing that they measured the time it took an electron to leave a two-atom molecule after it had been illuminated with an extremely bright and short infrared laser pulse. While a two-atom molecule is relatively simple, their experimental technique "opens up a new avenue" to study how light interacts with electrons in more complex molecules, the authors wrote in the paper.

[...] In the experiment, the researchers measured how long it took for the electron to depart the molecule after the photons from the laser hit it. Specifically, they discovered that the electron reverberated back and forth between the two atoms for 3,500 attoseconds before it took off. To put that into perspective, that is a quadrillion times faster than the blink of an eye, which takes a third of a second.

[...] In this experiment, the researchers engineered the laser light's polarization to rotate steadily, as though the crests and dips of the electromagnetic field were a corkscrew spiraling through space. That rotation could also track time, like the second hand of a clock. They assumed that, as the laser pulse illuminated the molecule, the electron started to leave it when the pulse peaked in brightness. At that peak intensity, the light would be polarized in a particular direction, according to the sweep of the wave as it rotated. By comparing the angle of the polarized beam to the angle at which the electron was ejected from the molecule, they could measure how long it took for an electron to leave the molecule. Physicists refer to this laser timing technique as the "attoclock" method, as it is capable of measuring durations on the attosecond scale.

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