Nonequilibrium dissociation of a molecular gas under the action of infrared resonance laser radiation

Afanas'ev, Yurii V; Belenov, É. M.; Poluéktov, I A

doi:10.1070/qe1973v003n02abeh004778

Cited by 5 publications

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“…Provided the electrons very rapidly acquire the same energy distribution (Afanas'ev et al 1970) under the optical frequency field as they would have under the equivalent static field Ee, we may relate vi and vex to the Townsend primary ionization coefficient a and excitation coefficient 19. Over ranges of interest 8/N, a/N and W are proportional to Ee/N so Here IC is a coefficient for a given gas which may be derived from a knowledge of values Figure 1 illustrates the dependence of v/N upon E,/" deduced from data of 8, 01 and W.…”

Section: Diffusion Dominated Lossesmentioning

confidence: 99%

Laser beam induced breakdown in helium and argon

Morgan

Evans

Morgan

1971

J. Phys. D: Appl. Phys.

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Measurements of the laser radiation power density Pth required to cause ionization growth and breakdown in the pressure ranges 1800 less-than-or-eq, slant p less-than-or-eq, slant 16 000 torr and 200 less-than-or-eq, slant p less-than-or-eq, slant 20 000 torr have been made in helium and argon, respectively. Three Q-switched lasers (ruby, Nd, and dye) were used to investigate the dependence of Pth upon pressure, radiation frequency ω and flash duration 2τ. Values of Pth lie between 1011 W cm−2 at low pressures and 1010 W cm−2 at high pressures.The experimental results are compared with expressions based upon an extrapolation of classical microwave breakdown theory to optical frequencies. Reasonably good agreement between measured and calculated threshold intensities is obtained.The interaction between the laser radiation and the gas proceeds via inelastic electron-atom collisions and photoionization. Three pressure regimes may be specified: a low pressure regime in which the threshold intensity and ionization growth rate are governed principally by diffusion losses, an intermediate régime in which the laser flash duration is the dominant factor and a high pressure régime where electron-ion recombination controls the rate of ionization growth and the onset of breakdown. The ionization rate is shown to be proportional to the laser beam intensity and, in the intermediate régime, the threshold intensity Pth is proportional to ω2/τ at constant pressure. A value for the electron-atom momentum transfer collision frequency of about 3-4×109p and of about 5 eV for the electron mean energy is derived for argon at the onset of breakdown.

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Section: Diffusion Dominated Lossesmentioning

confidence: 99%