The 2023 Nobel Prize in Physics was awarded to 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.” An attosecond is a billionth of a billionth of a second, and it is at this timescale that movements of electrons in atoms and molecules take place. The key to observing the world of electrons is the interaction between atoms and intense laser pulses, leading to photon emission that is observed as a flash of light – measurable in attoseconds.
Anne L’Huillier’s journey of this discovery began when she was a researcher at the Commisariat à l’Energie Atomique (CEA) in Paris. She participated in an experiment with the aim to measure the fluorescence light emitted from atoms or ions exposed to an intense infrared laser. “Not much fluorescence was seen,” said L’Huillier during her Nobel Lecture. “We observed mainly high-order harmonics of the laser field.” The intensities of the high-order harmonics plotted as a function of photon energy formed a plateau, meaning that the process was highly non-perturbative.
Over the next several years, many physicists around the world worked to understand the theory behind the experiment, and an intuitive picture known as the three-step model was formulated. When an atom is placed in a very strong laser field, an electron may tunnel ionize, is driven away by the laser field and may come back towards the atom. There is a small probability that the electron recombines back to the ground state, leading to the emission of short light bursts, with a duration of the order of a few hundred attoseconds. This process is repeated every half-laser cycle, and the frequency spectrum consists of high odd-order harmonics.
The experimental methods which motivate this Nobel Prize may have far-reaching applications, as electronic transitions in atoms and molecules underpin several processes in nature, from how DNA molecules can be damaged by ionization, to how light reacts with photovoltaic materials in solar cells. In addition, high-order harmonics are an interesting radiation source for the metrology of the next generation of integrated circuits. Many researchers believe this is only the beginning of the field.
Anne L’Huillier was born on 16 August 1958 in Paris. She studied at the Université Pierre et Marie Curie in Paris and the CEA, where she defended her thesis in 1986. She was then recruited at the CEA as a researcher. L’Huillier completed two postdoc positions, at Chalmers University of Technology in Gothenburg and the University of Southern California, Los Angeles. L’Huillier became part of the faculty at Lund University in 1995 and Professor of Physics in 1997. She is married and has two children.
