An attosecond is to a second as a second is to the age of the Universe. 0.0000000000000000001 (that’s 18 zeros!) seconds. It’s a timeframe so short that there’s no relatable example from our macro world. It’s a unit reserved for describing how quickly electrons move between energy levels within an atom.
For those studying electron dynamics in novel materials (for use in ultrafast electronics and quantum systems) or in molecules for medical diagnosis, an attosecond is the time resolution needed on the electron camera to take a snapshot of this fundamental particle in action. And thanks to 2023’s winners of the Nobel Prize in physics, we now have a way of doing just that, with the development and demonstration of attosecond laser pulses.
The journey to the Nobel-winning discovery started with French-Swedish physicist Anne L’Huillier and a process called high-harmonic generation. When a red laser passes through a gas, the light that is emitted will contain very specific slices of the colour spectrum that are shorter in wavelength (higher in frequency): green, blue, UV and x-ray.
L’Huillier provided the theoretical description that explained how these harmonics of the laser beam were generated when it passes through a gas. From here, the jump was made to predict that, in the right conditions, these harmonic light frequencies will superimpose to form a train of attosecond pulses.
Fast forward 10 years to Pierre Agostini and Ferenc Krausz, who led teams that demonstrated attosecond pulses of light experimentally for the first time. Crucially, Krausz managed to pick off a single pulse of this train as a flash probe to freeze-frame an electron being pulled away from the atom.
These super-short light pulses are the key to recording the movement of electrons, so that we can better understand them. This will help us manipulate and design materials for technologies of the future that will affect all of our lives. For their combined efforts, L’Huillier, Agostini and Krausz equally share the Nobel Prize.
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