“VU Experts Help Understand”: Three Scientists Win the Nobel Prize in Physics for Creating Attosecond Pulses of Light

This year’s Nobel Prize in Physics was jointly awarded to the French scientist working in the US – Prof. Pierre Agostini, the Hungarian and Austrian scientist working in Germany – Prof. Ferenc Krausz, and the French scientist working in Sweden – Prof. Anne L’Huillier. They have been awarded the prize for the experimental methods they created to generate attosecond pulses of light for the study of electron dynamics in matter.

Prof. Mikas Vengris, Research Professor at the Laser Research Center of the Faculty of Physics of Vilnius University (VU), says that although discussions about the application of the discovery for industrial, medical, or business use are premature, these pulses have already been used in cutting-edge research within physical, chemical, and materials science.

Physics of extremely short and very high-frequency pulses of light

Prof. M. Vengris explains the concept of the physics of extremely short and very high-frequency pulses of light: ‘If we imagine light as a wave spreading in space, the shortest possible flash of light in space is equal to the length of one cycle of a wave moving upwards and downwards through crests and dips. Since the speed of light is always the same – 300 thousand kilometres per second – for visible light, such a wave cycle corresponds to several femtoseconds. The movement of a small atom or atomic nucleus can be detected in a few femtoseconds.’

According to the VU professor, electrons are two thousand times lighter than their nuclei, and the speed of motion is faster by a thousand times. Thus, in order to track their movement, attosecond flashes of light must be employed as they correspond to much shorter waves, for the experimental demonstration of which Professors P. Agostini, F. Krausz, and A. L’Huiller have been awarded.

Prof. M. Vengris highlights that these experiments are a logical sequence to the previous laser experiments: ‘The difference is that they allow much faster processes to be studied, e.g. to observe how the light frees the electron from matter; this requires completely different experimental methods. Radio waves and visible light are the same electromagnetic waves, after all, but a radio set is very different from a camera. Thus, the attosecond optics are very different from the femtosecond optics.

Attosecond pulse – just like a stroboscopic flash at a disco

‘Attosecond is a very short period of time. There are approximately the same number of attoseconds in a second as there have been seconds since the Big Bang. The extremely short duration of the light flashes allows them to be used in a detailed study of the movement of electrons in matter. As attoseconds go by, the environment of electrons – atoms and molecules – have no time to move; it is as if they are ‘frozen’. Thus, when observing electrons, the attosecond pulse can be compared to a stroboscopic flash at a disco, where dancers seem to be frozen in different poses with every flash of light. Sensitive detectors register such ‘poses’ of electrons in the experiment’, explains Prof. M. Vengris.

Just as in the case of (almost) any other Nobel Prize, he says that it is important to not only appreciate the contribution made by the laureates themselves but also to value the input of other scientists working in this field, even though they have not been awarded the prize. It is only thanks to the joint work of all scientists that the topic of attoseconds has become relevant and deserving of the Nobel Prize.

Concerning the specific laureates, Prof. A. L’Huiller demonstrated that shining an intense infrared laser beam on a noble gas produces laser-frequency overtones, known as harmonics from music (a note played by the piano sounds different from the note played by a violin precisely due to higher order harmonics). This led to the development of a way to shorten the length of waves of laser radiation and then generate shorter pulses from those shorter waves. The means of generating bursts of such attosecond flashes was devised by Prof. P. Agostini, who measured, for the first time, the duration of one such flash, lasting for approximately 250 attoseconds. F. Krausz was the first to generate and characterise individual flashes in detail; Andrius Baltuška, VU graduate and now a professor at Vienna University of Technology, has worked in his laboratory for some time,’ adds Prof. M. Vengris.

Lithuania is synonymous with lasers

According to the VU professor, the discussions regarding the practical applications for industrial, medical, or business use are premature: ‘Technologically, attosecond pulse lasers are now equivalent of the computers of the previous age that used to occupy large buildings and consumed a lot of power. However, these pulses have already been applied at the forefront of cutting-edge research in physical, chemical, and materials science. There is no doubt that as they develop, new technologies will emerge, making these lasers cheaper, smaller, and more economical. Thus, we will surely see them in the micro- (or maybe nano- or pico-) electronics, medicine, and industrial production.’

Regarding whether Lithuanians work in this field, Prof. M. Vengris emphasises that Lithuania is synonymous with lasers and short pulses: ‘I, myself, am currently working with colleagues on the attosecond spectroscopy and visual experimental system. Lithuanian laser scientists – both VU scientists, Light Conversion, and Ekspla laser manufacturers – have developed a series of lasers called SYLOS. They are working on attosecond experiments at ELI ALPS, an Extreme Light Infrastructure facility of the European Union, in Szeged, Hungary.’

The interlocutor claims that Prof. A. Baltuška, successor to F. Krausz – this year’s Nobel laureate in Physics, undertook a large portion of the work for which the Nobel Prize was awarded. He contributed to these discoveries during his postdoctoral traineeship with F. Krausz.

P. Agostini is a Professor at the Ohio State University (US), and F. Krausz is the Director of the Max Planck Institute of Quantum Optics in Germany. A. L’Huillier, Professor at Lund University (Sweden), is only the fifth woman to win the Nobel Prize in Physics since 1901.