MOSCOW, October 3, Vladislav Strekopytov. The Frenchmen Pierre Agostini, Anne L'Huillier and the Hungarian Ferenc Krausz, who developed a way to create extremely short pulses of light, were awarded the Nobel Prize in Physics. Their discovery makes it possible to measure very fast processes, for example, the movement of electrons in an atom.
Ultrafast physics
Any person familiar with photography knows: the faster the event, the shorter there must be a shutter speed at which the photo is taken. Modern lasers are capable of generating pulses of radiation lasting several femtoseconds (ten to the minus 15th power of a second). Such a laser “strobe” is capable of recording the movement of atoms in molecules.
This year's Nobel laureates in physics received pulses of light in the attosecond (ten to the minus 18th power of a second, or one billionth of a billionth of a second) range of light — already capable of capturing what happens inside atoms. To understand what small units of time we are talking about, it is enough to say that a beam of light travels the distance from one wall of a room to another in ten billion attoseconds.
“Scientists are striving to study ever faster processes, because they have their own physics that we usually don’t see,” says Academician Alexander Sergeev, scientific director of the National Center for Physics and Mathematics (NCFM) in Sarov. “This achievement makes it possible to consider the movement of electrons in atoms and more complex structures. This is a new frontier of knowledge, moving deeper into the time scale.»
The femtosecond has long been considered the limit for light flashes. Existing technologies could not advance further; something completely new was required. The scientists who were awarded the Nobel Prize essentially laid the foundations of a new, attosecond physics.
High overtones of light
Light consists of waves—oscillations of electric and magnetic fields. In 1987, Frenchwoman Anne L'Huillier, now at Lund University in Sweden, discovered that when an infrared laser beam passes through a noble gas, many overtones of light are produced. This is approximately how the vibrations of a string give rise to different harmonics of sound: along the entire length of the string — the main tone, half — the second overtone, a third — the third, and so on. L'Huillier found that each overtone of a light wave with a given number of cycles is determined by the interaction of the laser beam with gas atoms.
In 2001, Hungarian Ferenc Krausz, now director of the Max Planck Institute for Quantum Optics in Germany, working with hard ultraviolet radiation in an inert gas and using nonlinear optics methods, obtained a single light pulse with a duration of 650 attoseconds. At the same time, the French-American experimental physicist Pierre Agostini, using an original laser profile reconstruction technique called RABBITT, created a series of pulses of 250 attoseconds.
L'Huillier and her colleagues used attosecond laser pulses to study the movement of electrons in atoms and molecules in real time. The two laser sources sent short pulses with a slight delay relative to each other. A combined beam with attosecond peaks appeared.
Shorter and more powerful
In 2018, the Nobel Prize was already awarded for discoveries in this area. Then we were talking about femtosecond, but very intense optical pulses.
“Powerful fields and short pulses are connected,” explains Sergeev. “For a powerful field, you need to generate very short pulses, and vice versa, intense laser radiation allows us to move further into the time scale. And this helps to better understand the structure of matter.”
» We in Russia are very actively working in this direction. At NCFM, the topic of ultra-strong laser fields and ultrashort attosecond pulses is one of the main ones. We are very pleased that the research of our colleagues abroad has been awarded such a high award,» says the academician.
< h3 id="1900269042-4">What does this give in practice
Attosecond pulses are necessary to study any fast processes that were hitherto considered instantaneous. First of all, these are chemical reactions. Now they can be decomposed into stages, which means changes can be made in their course.
“We have received a modern diagnostic tool for studying matter,” concludes Sergeev. “In fact, we are talking about new materials science, the cutting edge of diagnostics, when we observe processes with very detailed spatial and at the same time temporal resolution. A world in a different range is opening up to us.»
Ultrashort pulses are important for condensed matter physics, chemical technologies, bio- and photochemistry, medical diagnostics, microelectronics. In a word, wherever you need to understand the subtle structure of matter and control the behavior of electrons.