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Title: Investigating the dynamics of laser induced sparks in atmospheric helium using Rayleigh and Thomson scattering

We have used optical Rayleigh and Thomson scattering to investigate the expansion dynamics of laser induced plasma in atmospheric helium and to map its electron parameters both in time and space. The plasma is created using 9 ns duration, 140 mJ pulses from a Nd:YAG laser operating at 1064 nm, focused with a 10 cm focal length lens, and probed with 7 ns, 80 mJ, and 532 nm Nd:YAG laser pulses. Between 0.4 μs and 22.5 μs after breakdown, the electron density decreases from 3.3 × 10{sup 17 }cm{sup −3} to 9 × 10{sup 13 }cm{sup −3}, while the temperature drops from 3.2 eV to 0.1 eV. Spatially resolved Thomson scattering data recorded up to 17.5 μs reveal that during this time the laser induced plasma expands at a rate given by R ∼ t{sup 0.4} consistent with a non-radiative spherical blast wave. This data also indicate the development of a toroidal structure in the lateral profile of both electron temperature and density. Rayleigh scattering data show that the gas density decreases in the center of the expanding plasma with a central scattering peak reemerging after about 12 μs. We have utilized a zero dimensional kinetic global model to identify the dominant particle species versus delay time and this indicates that metastable helium and the He{sub 2}{sup +} molecular ion playmore » an important role.« less
Authors:
; ; ; ;  [1] ; ;  [2] ;  [3]
  1. Department of Physics and Astronomy, Centre for Plasma Physics, Queen's University Belfast, Belfast BT71NN (United Kingdom)
  2. Department of Physics, Wesleyan University, Middletown, Connecticut 06459 (United States)
  3. Department of Energy Sciences, Tokyo Institute of Technology, Yokohama 2268502 (Japan)
Publication Date:
OSTI Identifier:
22399197
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 1; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; BREAKDOWN; ELECTROMAGNETIC PULSES; ELECTRON DENSITY; ELECTRON TEMPERATURE; ELECTRONS; EV RANGE; HELIUM; HELIUM IONS; LASER-PRODUCED PLASMA; MOLECULAR IONS; NEODYMIUM LASERS; PLASMA EXPANSION; RAYLEIGH SCATTERING; THOMSON SCATTERING; TIME DELAY