Considerações sobre a ruptura dieletrica em gases sob ação de um campo de laser intenso

AUTOR(ES)
DATA DE PUBLICAÇÃO

1985

RESUMO

Gas breakdown, steady-state maintenance and continuous generation of low-temperature plasma and propagation of the plasma fronts are important subjects of past and current research on laser induced gas discharges. This Thesis is concerned with some aspects of the laser induced dielectric breakdown in a gas. We have specifically addressed the question of the onset of the breakdown process. In dealing with the equation describing the energy balance between the laser delivered energy and the energy consumption to establish the avalanche produced discharge plasma, we have introduced new features that had not been considered previously. We refer to accounting for thellaser induced effects upon the atomic ionization threshold and upon the effective rate of collisions leading to inverse bremsstrahlung. Their influence upon the threshold laser intensity Jcr needed to produce the gas breakdown is fully explored. This led to a Jcr vs. gas pressure p prediction that qualitatively described the experimental data available for atomic hydrogen breakdown under rubi laser irradiation. However, for a better description, it turned out that an assumed estimate of the electronic density within the breakdown volume had to be revised. In fact, we had to resort to a phenomenological estimate of ne(p) = a(p) n(p), where n(p) is the gas atomic density (atoms/cm3) at pressure p. The pressure dependence of a(p) depends upon the balance, within the focal volume, between electronic gain (electronic production by multiphoton ionization initiated avalanche - impact ionization+inverse bremsstrahlung through many generations) and electronic loss, (due to various loss mechanisms both of electronic energy - non-ionizing impacts - and of electrons themselves - recombination, electronic runaway, etc.). The formidable task of trying to produce a(p) on first principles treatment of such processes, including laser effects upon them, was for the moment out of question so we decided to calculate a(pi) values based on the experimental data available for threshold fluxes. These a(Pi) values were computer fitted to obtain the function a(p) which was then used to establish the theoretical prediction of the critical laser power needed to induce the gas breakdown, as a function of the gas pressure, with due account taken of the laser effects upon the relevant atomic gas parameters

ASSUNTO(S)

laser em fisica campos eletromagneticos dieletricos ionização de gases

ACESSO AO ARTIGO

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