Features of Gas Breakdown by Short Pulses of THz Radiation

Le résumé fourni par la source

The terahertz range lies intermediate between the IR and radio-frequency ranges. Each of them is thoroughly studied, both in terms of creating radiation sources and in terms of their application [1], [2]. At the same time, the terahertz range has a number of specific features that make it unique for a wide range of applied research in the fields of physics, chemistry, biology, medicine and engineering. This article provides both experimental data and a theoretical calculation of the threshold values of the electric field of breakdown of heavy noble gases by short pulses of THz radiation. The experiment was carried out on the terahertz Novosibirsk free-electron laser NovoFEL, which has in the investigation an average power of 250 W, a pulse duration of 120 ps and a repetition rate of 5.6 MHz [3]–[5]. The electric field value in the beam waist was about$1 \text{MV} / \text{cm}$. In the theoretical description of the breakdown phenomenon, it turned out that the oscillatory energy of electrons in such an alternating field was about 2 eV. The electron quickly gains energy between collisions. Thus, the electron overcomes the gap between the excitation and ionization energies by several collisions. When comparing the results of the theoretical calculation and experimental data, it turned out that such a high rate of electron heating and relatively rare non-elastic collisions lead to the fact that electron-impact ionization is not instant process of excited atoms as in breakdown theory for long-pulse or continuous radiation. This occurs at an energy when the ionization cross section begins to exceed the excitation cross section. The energies are 34 eV for Ar and 29 eV for Kr.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.