The Nobel Committee in Stockholm had to call physicist Anne L’Huillier no fewer than four times this morning before she finally answered. She was teaching in Lund and was now on a break. The committee told her that she is one of three scientists to be awarded the Nobel Prize for Physics. After the announcement, she immediately continued with her lectures. “Education is very important,” L’Huillier said at a press conference an hour later. “But the last half hour of the lecture was difficult. I am very touched.”
This year’s Nobel Prize in Physics goes to research into ultra-short time scales. The prize was awarded to Pierre Agostini, Ferenc Krausz and therefore Anne L’Huillier for their experiments that “have given humanity new tools for exploring the world of electrons in atoms and molecules” – tools that, according to the committee, can be used in the future help recognize diseases and improve electronics.
Attoseconds
Electrons move very quickly and anyone who wants to study these movements must observe them on extremely short time scales, just like a photographer does a special high speed camera takes to capture a picture of the wings of a rapidly flapping hummingbird. Electrons involve time scales of attoseconds: one trillionth of a second. By comparison, the duration of one human heartbeat – a beat – contains approximately as many attoseconds as there are heartbeats in the age of the entire universe.
The three laureates came up with a way to take snapshots of electrons with extremely short laser pulses. Physicist Huib Bakker from the Amsterdam research institute AMOLF explains how this works. “You start with a relatively long light pulse, from a few to tens of femtoseconds. That is already very short, but still a factor of a thousand longer than the attosecond. You send that light pulse through a cloud of noble gas atoms, for example xenon or argon, in which electrons are strongly bound.”
Such a light pulse is a wave with peaks and valleys, says Bakker. “Only at the moment when the peak of the light wave passes through an atom, an electron is released from the atom. That electron then returns very quickly to the atom, where the energy of the electron is converted into light that is emitted as a very short pulse. These flashes of light last so short that their duration is expressed in attoseconds.”
By firing the resulting ultra-short light pulses at a molecule, physicists can take a snapshot of the movement of the electrons in that molecule and study their behavior. But even then the image is still blurry. For example, they can see on which side of the molecule the electron is located, but not where exactly.
Future music
This technique offers opportunities for various applications, including in medicine. “All chemical reactions, including those in our bodies, have to do with how electrons move,” says Bakker. “So if you understand how electrons move, it makes it possible to control chemical reactions. But to make conduction in semiconductors faster and more efficient, it is also useful to understand why an electron gets stuck somewhere. But this is all still in the future.”
That is why Bakker is also surprised. “The Nobel Prize for Physics is usually awarded to techniques that have been proven for a long time, but this research has not been going on for that long. Only in recent years has the technique actually been used to study molecules. The research is still very fundamental physics. It’s wonderful that this is appreciated.”
Jan Versluis, also from AMOLF, is surprised, just like Bakker. “It is very fundamental research and appeals much less to the imagination than, for example, research into black holes. But attosecond research is also a huge technical achievement.”
The physicists will all receive the same share of the prize of 11 million Swedish crowns (950,000 euros) for their discovery.
L’Huillier noticed a strange effect in 1987 when she shone infrared laser light into noble gas. Some electrons gained extra energy that was then emitted as light. With her discovery she laid the foundation for further research.
Since the beginning of this century, Agostini and Krausz have been independently using L’Huillier’s insights in various experiments to produce short light pulses. Agostini’s pulses lasted only 250 attoseconds. That of Krausz 650.
Huge honor
Wim Ubachs of the Vrije Universiteit, who has published several scientific articles with L’Huillier, says that she conducts her research very precisely. “Everything has to be right for her. A good quality for a physicist.” Ubachs worked with L’Huillier when she and her husband were still working on the picosecond, which lasts a million times as long as the attosecond.
It is only the fifth time that a woman has been awarded the Nobel Prize for physics. Marie Curie preceded L’Huillier in 1903, Maria Goeppert-Mayer in 1963, Donna Strickland in 2018 and Andrea Ghez in 2020. “As you know, there are not many women who have won this most prestigious award,” said L’Huillier therefore against the committee. “This is a tremendous honor.”