Laser Key: Plasma "thermometers" will help create indestructible spaceships

Russian scientists have proposed a technique that will help to observe in real time the temperature distribution in a "cloud" of plasma flares that occur when laser beams interact with materials. The proposed technology will make it possible to improve the processes of creating microchips, as well as thermal protection for reusable spacecraft and spacecraft. Researchers have already started experimenting with such materials. For more information, see the Izvestia article

How to look inside a red-hot plasma

Scientists from Lomonosov Moscow State University have proposed an innovative technique and equipment for non—contact investigation of hot plasma, an ionized gas flare that occurs at extremely high temperatures. The research was carried out under a grant from the Russian Science Foundation (RSF).

According to the developers, such a "thermometer" makes it possible to look inside a rapidly changing incandescent "cloud" and build a real-time map of the temperature distribution inside it. This, in turn, allows us to draw conclusions about the composition and structure of the material.

— Plasma is a gas of charged particles. It is used in many technical tasks. For example, when studying the properties of a material, researchers "hit" it with a laser pulse. As a result, part of the substance on its surface ionizes and evaporates, forming a plasma flash. This bundle of energy lives for microseconds, but complex processes take place inside it. The proposed method allows us to obtain a thermal "portrait" of this area," Timur Labutin, a project participant and associate professor of the Department of Laser Chemistry at Moscow State University, explained to Izvestia.

Photo: courtesy of Timur Labutin

Among other things, he explained, the development opens up opportunities for improving technological processes in the space industry, aircraft manufacturing, microelectronics and other areas where plasma with strictly defined parameters is used.

According to the expert, the fluorescence effect is at the heart of the new approach. Scientists use one laser to create a flash, and the other to affect the particles inside the ionized area in a special way. As a result, the electrons in the atoms jump to higher energy levels, which causes them to fluoresce, and experimenters record this glow with optical devices.

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One of the advantages of the study is that the developers were able to deduce and confirm a formula that relates luminescence and temperature.

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As Timur Labutin explained, the technique of using laser beams and fluorescence to study plasma is generally known. But before that, it was used for relatively cold sources, such as flames. In the case of laser plasma, which is much hotter, this scheme does not work for physical reasons. Therefore, scientists had to refine the method to overcome the limitation.

— Although the development is focused on fundamental research, it has many practical applications. For example, in microelectronics, laser spraying of a thin film onto a substrate is used in the manufacture of microchips or solar cells. Our development will help to more accurately determine the plasma parameters and achieve an even distribution of the material. This will make it possible to avoid defects and improve the quality of products," the specialist shared.

Photo: Global Look Press/Frank Röder

At the same time, he added, the new method makes it possible to study processes similar to those that occur during the hypersonic entry of various objects into the dense layers of the atmosphere. In particular, meteors or artificial spacecraft. Due to intense heating, their surface heats up, forming a plasma layer of ionized air particles.

Understanding how temperatures are distributed inside this fiery cocoon will help create effective plasma-resistant structural elements and heat shields that will allow reusable spacecraft to return to Earth without destruction. Currently, experts have started experimenting with samples of such coatings.

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What tasks will the innovative device perform?

In the next step, the researchers plan to automate the measurements to increase the resolution and speed of plasma scanning. Also among the promising tasks is the application of the method to study other plasma sources: from electric arcs to spark discharges.

— Plasma diagnostics are needed in a variety of applications, ranging from spectral analysis of samples to the study of thermonuclear fusion. However, in some cases there are limitations," Alexey Ilyin, a senior researcher at the Institute of Automation and Control Processes at the Far Eastern Branch of the Russian Academy of Sciences, told Izvestia. — For example, to study plasma with a femtosecond laser (with a pulse frequency on a femtosecond scale — one quadrillionth of a second. — Izvestia) the development is probably also inapplicable, since it requires a narrow-band filter. This method is also not suitable for studying thermonuclear reactions, since when the electron concentration is close to critical, the laser beam will be reflected rather than absorbed. In all other cases, a new approach will be in demand.

Photo: courtesy of Timur Labutin

At the same time, he added, for the development of the proposed technique, a laser with a tunable wavelength and a narrow spectral line will be required to selectively excite fluorescence lines.

— The results of the study, first of all, can be used to develop diagnostic methods. At the same time, they open the way to the development of laser-plasma nanostructuring technologies that make it possible to create materials with unique electrophysical, optical and other properties," said Andrey Karmanov, Associate Professor of the Department of Nano and Microelectronics at Penza State University.

At the same time, obtaining a thermal "map" of a plasma clot with high spatial resolution is only one of the tasks that need to be solved in this field. Another, and perhaps more important, is high—precision plasma temperature control, the specialist emphasized. Both in the central zone and on the periphery. Combining these approaches will make it possible to study the processes that occur when a substance is irradiated with a laser at a new level, as well as to control the nanostructuring of materials.