Physicists at Moscow State University have traced the change in ionization mechanisms from the visible to the mid-IR range

Researchers at the Physics Department of Moscow State University have traced the change in ionization mechanisms from the visible to the mid-IR range. The research will help to develop new methods of microprocessing, will bring the creation of new types of sensors closer, and will also be useful in biomechanics and rehabilitation engineering. The results were published in Scientific Reports.

Currently, laser technologies are actively moving into adjacent wavelength ranges inaccessible to the human eye – X-ray and infrared (IR) regions. The history of laser sources in the mid-IR wavelength range (2.5-25 μm) dates back practically to the invention of the lasers themselves (since 1964). The sources of radiation created today in the mid-IR range, in contrast to their predecessors, have an ultrashort duration of up to tens of femtoseconds (10-15 s). Changing the wavelength and duration of a laser pulse in comparison with previously available sources leads to a new character of the interaction of radiation with matter.

A group of scientists from the Department of General Physics and Wave Processes of the Physics Faculty of Moscow State University is investigating the mechanisms of breakdown of matter (dielectrics and semiconductors), that is, irreversible changes in the structure, under the influence of laser radiation with different wavelengths. For ultrashort radiation, the first step towards material damage is plasma generation – excitation and ionization of atomic electrons. The ionization mechanisms depend on the wavelength of the incident radiation. In the visible wavelength range, multiphoton ionization predominates, while in the mid-IR range, electrons are generated due to the tunneling mechanism. The generated electrons then begin to increase their energy (heat up) by interacting with the laser pulse. The nature of this interaction also depends on the wavelength. In the visible region of the spectrum, heating is extremely ineffective. In the 3-4 μm wavelength range, electrons increase their energy very quickly. However, at long wavelengths, the heating mechanism changes again and the effective energy gain stops. “In this work, for the first time, we were able to trace the change in the described mechanisms from the visible wavelength range to the mid-IR, both experimentally and using numerical simulation. The information obtained allows us to judge the dependence of the material damage threshold on the wavelength “, – said “In this work, for the first time, we were able to trace the change in the described mechanisms from the visible wavelength range to the mid-IR, both experimentally and using numerical simulation. The information obtained allows us to judge the dependence of the material damage threshold on the wavelength “, – said “In this work, for the first time, we were able to trace the change in the described mechanisms from the visible wavelength range to the mid-IR, both experimentally and using numerical simulation. The information obtained allows us to judge the dependence of the material damage threshold on the wavelength “, – saidFedor Potemkin , Associate Professor, Department of General Physics and Wave Processes, Faculty of Physics, Moscow State University.

Physicists of the Moscow State University independently develop femtosecond sources of laser radiation in the mid-IR range, which allows them to monitor and control the parameters of laser pulses for carrying out such experiments. MSU has developed its own methods for registering the process of plasma generation (for example, using the process of generating the third harmonic), measuring its parameters and evolution. The combination of this experience allows scientists from Moscow State University to independently conduct all experimental research. In addition, in this work, the authors from Moscow State University have also developed a theoretical model and written a set of programs for calculating ionization processes.

The results obtained are important for the development of the technological base of optical components in the mid-IR range, since the development of laser sources themselves requires optical coatings and elements with high radiation resistance. “Understanding the ionization mechanisms prior to breakdown allows us to control this phenomenon. In particular, the creation of modified regions with controllable morphology, size, and structure is an important task of laser micromachining. Since pulses with different wavelengths interact differently with matter, multispectral exposure (for example, by using a pair of pulses with different wavelengths) can lead to an increase in the accuracy of the micromachining process, making it more controllable and predictable. New micromachining techniques are important, for example

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