Extended plasma channels created by UV laser in air and their application to control electric discharges
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Extended Plasma Channels Created by UV Laser in Air and Their Application to Control Electric Discharges V. D. Zvorykina,b, A. A. Ionina, A. O. Levchenkoa, L. V. Selezneva, D. V. Sinitsyna, I. V. Smetanina, N. N. Ustinovskiia, and A. V. Shutova a
b
Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 119991 Russia National Research Nuclear University Moscow Engineering Physics Institute, Kashirskoe sh. 31, Moscow, 115409 Russia e-mail: [email protected] Received April 9, 2014
Abstract—Results are presented from a series of experimental and theoretical studies on creating weakly ionized extended plasma channels in atmospheric air by 248-nm UV laser radiation and their application to control long high-voltage discharges. The main mechanisms of air ionization by UV laser pulses with durations from 100 fs to 25 ns and intensities in the ranges of 3 × 1011 −1.5 × 1013 and 3 × 10 6 –3 × 1011 W/cm2, respectively, which are below the threshold for optical gas breakdown, as well as the main relaxation processes in plasma with a density of 109–1017 cm–3, are considered. It is shown that plasma channels in air can be efficiently created by amplitude-modulated UV pulses consisting of a train of subpicosecond pulses producing primary photoelectrons and a long UV pulse suppressing electron attachment and sustaining the density of free electrons in plasma. Different modes of the generation and amplification of trains of subterawatt subpicosecond pulses and amplitude-modulated UV pulses with an energy of several tens of joules were implemented on the GARPUN-MTW hybrid Ti:sapphire–KrF laser facility. The filamentation of such UV laser beams during their propagation in air over distances of up to 100 m and the parameters of the corresponding plasma channels were studied experimentally and theoretically. Laser initiation of high-voltage electric discharges and control of their trajectories by means of amplitude-modulated UV pulses, as well as the spatiotemporal structure of breakdowns in air gaps with length of up to 80 cm, were studied. DOI: 10.1134/S1063780X15010067
1. INTRODUCTION The possibility of creating extended (up to several hundred meters long) conducting plasma channels in atmospheric air by means of laser radiation has attracted considerable attention since the 1970s. Interest in these studied is motivated by the importance of potential practical applications of such channels, which can be used to remotely monitor atmosphere contamination (e.g., by using a nitrogen laser operating in the mode of one-passage radiation amplification in the plasma channel [1]), provide wireless transmission of the electric current [2, 3], create virtual plasma waveguides for RF and microwave beams with the purpose of reducing their natural divergence [4– 8], and develop active systems of lightning protection (including laser initiation and control of the lightning trajectory; see, e.g., [9–12] and references therein). The latter problem implies preliminary studies of high-voltage laser-induced
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