Tracing Air-Breakdown Plasma Characteristics from Single-Color Filament Terahertz Spectra
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Tracing Air-Breakdown Plasma Characteristics from Single-Color Filament Terahertz Spectra D. V. Mokrousova1 · S. A. Savinov1 · L. V. Seleznev1 · G. E. Rizaev1 · A. V. Koribut1 · Yu. A. Mityagin1 · A. A. Ionin1 · I. A. Nikolaeva2 · D. E. Shipilo1,2 · N. A. Panov1,2 · A. A. Ushakov3 · A. B. Savel’ev1,2 · O. G. Kosareva1,2,4 · A. P. Shkurinov2,5 Received: 18 October 2019 / Accepted: 17 March 2020 / © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this paper, we measure broadband terahertz spectra from a single 744-nm filament produced in tight, medium, and loose geometrical focusing conditions. Terahertz spectra are measured using interferometer coupled to a helium-cooled bolometer avoiding any cutoff frequencies. Based on THz spectrum maximum position and spectral width, we estimate electron-heavy particle (neutrals and ions) collision rate. Numerical simulations are performed using the state-of-the-art model of unidirectional femtosecond pulse propagation and convergence/divergence of optical radiation at large angles. Keywords Broadband terahertz generation · Femtosecond pulse · Air breakdown plasma · Collision rate
1 Introduction Terahertz (THz) emission from optical breakdown of gases [1, 2] has been actively studied for the past 20 years [3, 4]. Single-color filament was found to irradiate in O. G. Kosareva
[email protected] 1
P. N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia
2
Faculty of Physics, International Laser Center, M. V. Lomonosov Moscow State University, Moscow, Russia
3
A. M. Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia
4
Institute of Modern Optics, Nankai University, Tianjin Key Laboratory of Micro-scale Optical Information Science and Technology, Tianjin, China
5
Institute on Laser and Information Technologies of Russian Academy of Sciences - Branch of the Federal Scientific Research Center “Crystallography and Photonics” of Russian Academy of Sciences, Shatura, Moscow Region 140700, Russia
International Journal of Infrared and Millimeter Waves
THz range into a cone with an angle which increases as the length of the filament decreases [5, 6]. The tighter the focusing geometry, the larger the cone angle of THz radiation. The physical mechanism of THz emission was proposed to be radiation pressure force and ponderomotive force [7]. The intensity of THz radiation from a single filament is two orders of magnitude lower than the intensity of THz radiation from a dual-color filament [2] or from a DC-biased filament [8, 9]. At the same time with the developing technique of regularized superfilamentation from 800nm Ti:sapphire laser [10–13], the conversion efficiency to THz in a single color is expected to be enhanced by a factor of 2–5 [14]. There are a lot of spectral measurements of THz radiation from two-color filament; however, the ones for single-color filament are quite rare [3]. So, the detailed measurements of THz radiation spectra from a single-color ultraviolet filam
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