— What does attosecond physics do, how did it appear and why was it singled out as a separate field?
— Attosecond physics arose as a result of the symbiosis of two major scientific directions - laser physics and physics that studies the interaction of laser pulses with atoms and molecules. Essentially, attosecond physics is the study of wave processes on the attosecond scale. An attosecond is a second to the minus eighteenth power, and if we make visual comparisons, then in one second as many attoseconds pass as the number of seconds that have passed during the existence of the Universe - approximately 14 billion years. Or I’ll give another analogy: it is known that nothing can exceed the speed of light, this is the fastest thing that exists in nature. And the light that is emitted by the Sun reaches the Earth in about 8 minutes. Now let’s take one atom, for example, hydrogen, the diameter of which is one angstrom - ten to the minus tenth of a meter. So, light travels this distance in one attosecond. These are incredibly short time intervals, which we, of course, do not operate in everyday life and which are even difficult to imagine.
About 20 years have passed since the founding of attosecond physics, which is not much by scientific standards. It all started with single experiments on the production of laser pulses of attosecond duration. First, they managed to create a pulse lasting one femtosecond—that’s one quadrillionth of a second. Then physicists learned to create pulses lasting 800 attoseconds, and by 2016 - 300 or even 100 attoseconds.
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As I already mentioned, attosecond physics deals with the study of wave processes - these include electromagnetic phenomena, an alternating electromagnetic field. Or quantum objects - atoms and molecules that obey the laws of quantum physics. They differ from the laws of classical mechanics that we can observe in everyday life. Thus, at the quantum level, moving particles have wave properties that are described using the wave function. Therefore, when we talk about the wave processes that attosecond physics studies, we mean the movement of electrons and other quantum particles.
— That is, with the help of attosecond laser pulses you can “look” inside atoms and molecules?
— Yes, since the electronic structure of an atom changes over attosecond periods of time. Therefore, to detect such processes, we need tools that operate on the same time scale. It can be compared with regular photography, where the faster the subject moves, the shorter the lens shutter speed should be.
With the help of attosecond laser pulses, we can not only find out how the electronic structure of an atom changes in certain reactions and conditions, how these processes develop, but also influence them.
Electrons in atoms are distributed among levels; each level contains a certain number of electrons. You can imagine an atom as a box filled with rows of balls. And if you remove a ball from a row, then, naturally, the top balls will begin to fall into the resulting void. The same thing happens with an atom - if you pull out an electron from the inner shell (level), then an electron from the upper or lower level can come to this place. And if you want to photograph the process of this transition, you need a “camera” that fires faster than the electron makes its transition. Attosecond physics works in this area; it allows you to track the modification of the energy shells of the atom.
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— How do physicists get such short laser flashes?
— When a powerful laser pulse interacts with an atom, for example, hydrogen, an excitation occurs in the atom, which is emitted in the form of harmonics, or overtones. That is, secondary radiation at frequencies that are multiples of the original laser radiation. A parallel wave appears at a different frequency to the original one. And if you combine these waves, then if the phases of these waves coincide, the pulse will increase; if the phases combine in antiphase, then the field disappears. Thus, having a wide spectrum of such secondary waves, it is possible to obtain a narrow and isolated attosecond pulse as a result of coherent (synchronous
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) addition of these overtones. The Nobel Prize in Physics was awarded in 2023 for the development of a method for producing isolated attosecond pulses.
Today, the technology for producing attosecond laser pulses has already been developed in a number of countries; this is done in large laser centers where there are powerful lasers. Now the scientific community is faced with the task of increasing the power of attosecond pulses so that with their help it is possible not only to detect changes in the electronic structure of atoms, but also to influence it. Currently, the attosecond pulses obtained are low-intensity and have low power. How to strengthen them - the answer to this question has yet to be found.
— Your research group recently published a paper devoted to a new effect - controlled rectification of an attosecond pulse in a single atom. Please tell us more about this.
— First of all, it is necessary to explain what optical rectification is - an effect that was discovered at the dawn of nonlinear optics, a branch of physics that studies the propagation of light beams in solids, liquids and gases. The effect of optical rectification is that when laser radiation interacts with a substance, a constant electromagnetic field, a dipole moment, is formed in the latter. However, until now the effect of optical rectification could only be observed in some crystal structures, on relatively large objects. We have put forward a scientific hypothesis according to which a similar effect of optical rectification can be reproduced at the atomic level, inside an atom.
This is possible if attosecond laser pulses are applied to an atom placed in an intense infrared field.
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— Could this find some technical application?
— The technology of creating a dipole moment in atoms could, theoretically, find application in the creation of a new type of electronics. The fact is that now the entire element base is built on semiconductors, mainly silicon. In fact, information storage and processing in this case is carried out by moving electrons in the silicon substrate. However, this technology is reaching its limits, processor performance growth has slowed noticeably in recent years, and alternatives to silicon are being sought.
I would like to emphasize right away that this is only a hypothesis for now, but let us assume that atoms of any substance can act as such a carrier, which will change the dipole moment at an attosecond speed under the influence of a laser. In this case, the speed of calculations and computer performance can immediately increase by orders of magnitude.
— Are there plans to conduct experiments to confirm this hypothesis? Does Russia have the necessary capacity and equipment for this?
— Yes, in Russia there are a number of powerful laser installations - for example, there is such a laboratory at Moscow State University, and there is a similar center in Nizhny Novgorod and Sarov. That is, technically there is something to carry out such experiments in Russia; the equipment is available. However, attosecond research is not yet the focus of domestic experimental physics. Today, this area of research is most in demand in the USA, European countries and China. In our country, large laser centers and experimental physicists are concentrated on other areas of science. Russian high-power lasers are fully involved in other experiments, each of them was built for its own task. In order to develop attosecond physics, it is necessary, by and large, to open special laboratories that would deal specifically with this area.
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— In what other areas can attosecond physics be used or is it already being used? For example, how might it be involved in medicine and biochemistry?
— Attosecond physics may in the future open up the possibility of influencing the electronic structure of atoms, and it is this structure that is responsible for the chemical properties of substances. Therefore, if we learn to arbitrarily form electron density in atoms and molecules, this may allow us to create unique compounds and substances that will have new physical and chemical properties. In addition, there is a hypothesis according to which cancer and healthy cells respond differently to laser exposure, with the difference being tens of attoseconds. It was put forward by Nobel laureate in physics, German scientist Ferenc Kraus. In his opinion, using attosecond laser pulses it is possible to diagnose cancer and other diseases.
In fundamental science, attosecond technologies will help to look inside the atom and study in detail the dynamics of quantum processes. In general, the prospects for development in this area are extensive.
The material was prepared with the support of the press service of the Ministry of Education and Science.