The attoseconds one is among the most relevant scientific stories of the last 100 years - one of those stories where something seems impossible... until it is done. It is also one of those stories that perfectly tell how a scientific discovery is the result of collective efforts by a community of scientists working together, for decades, even at a distance (and they did it even when it was not mainstream).
And it is a story that culminates (but does not end) in 2023 with the awarding of the Nobel Prize in Physics to three scientists: Pierre Agostini, Ferenc Krausz and Anne L'Huillier, 'for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter'. Following this assignment, other scientists have emerged who have strongly contributed to the recent discoveries - and in particular one that concerns us very closely.
At the Department of Physics of Politecnico di Milano, Mauro Nisoli is Professor of Physics of Matter and Director of the Attosecond Research Centre laboratory. He is a pioneer of attosecond physics and the work of his research group is behind the experiments that led to the generation and characterisation of 'extremely short' light pulses, lasting a billionth of a billionth of a second, used to study the motion of electrons within atoms and molecules.
We asked him to tell us this story: here is how it went.
A GROUP OF PHYSICISTS WANT TO 'SEE' HOW ELECTRONS MOVE WITHIN MATTER AFTER INTERACTION WITH LIGHT
The story of this Nobel Prize - and of attoseconds - begins in the 1980s, when some scientists set out to look at what happens inside molecules - and atoms - when hit by a short, high-energy light pulse. But there’s a problem: electrons move faster than our instruments can pick up at the time. While the motion of atoms takes place on the femtosecond time scale (one femtosecond is equal to one millionth of a billionth of a second, namely 10-15 seconds), electrons move much faster, on the attosecond time scale, namely 10-18 seconds. Therefore, if we want to be able to follow (and measure) the motion of electrons, we must use laser pulses with durations of less than a femtosecond.
💡WHAT IS AN ATTOSECOND?💡
It is a unit of time and represents the time scale suitable for tracking the motion of electrons in atoms and molecules. One attosecond is equal to one millionth of a millionth of a millionth of a second. No comparisons exist that allow us to understand how small this unit of time is: we sometimes read that the number of attoseconds in a second is comparable to the number of seconds that have elapsed from the beginning of the Universe, 13.8 billion years ago, to today.
The point is... you cannot produce light pulses lasting shorter than one optical cycle, which is determined by the wavelength of light. Typically, a femtosecond laser produces pulses in the visible or near-infrared region. In order to generate attosecond pulses, the wavelength of light must first be shortened. In the 1980s this seemed an impossible feat. But still...
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