Mechanisms of resonant laser ionization |
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Authors: | A G Leonov D I Chekhov A N Starostin |
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Institution: | (1) Moscow Physicotechnical Institute, 141700 Dolgoprudnyi, Moscow Region, Russia;(2) Troitsk Institute of Innovative and Thermonuclear Research, 142092 Troitsk, Moscow Region, Russia |
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Abstract: | An experimental investigation and numerical simulation of resonant laser breakdown are performed. As a result, quantitative
agreement between the experimental data on the parameters of a dense resonant plasma (the electron density and the electron
temperature) and the results of calculations in the range of detunings of the laser radiation from resonance Δλ>2–2.5 nm, in which the spatial instability of the intense resonant laser beam and the absorption of radiation are minimal,
is obtained for the first time. It is shown that the previously proposed mechanism of resonant breakdown associated with laser-induced
associative ionization introduces only a small correction to the final extent of ionization of the resonant plasma and scarcely
alters its temperature. The influence of quantum stimulated inverse bremsstrahlung processes, which are usually described
as collisions of the second kind in the resonance case, on the energy gain by electrons is analyzed for the first time in
reference to specific experimental findings. The numerical calculations show that at detunings of the order of the Rabi frequency,
the mechanism by which electrons gain energy through the resonant system does not reduce to collisions of the second kind
and can significantly increase the density of the resonant plasma. However, in this range of detunings the laser beam is still
strongly perturbed by instability processes, precluding a proper comparison of the theory with experiment. At large Δλ the classical and quantum cases differ from one another only slightly, and the values of N
e calculated for both mechanisms lie within the measurement error.
Zh. éksp. Teor. Fiz. 111, 1274–1296 (April 1997) |
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