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Vapor Breakdown During ablation by Nanosecond Laser Pulses

Published online by Cambridge University Press:  21 February 2011

C. L. Liu
Affiliation:
Solid State Division, Oak Ridge National Laboratory Oak Ridge, TN 37831-6032
J. N. Leboeuf
Affiliation:
Fusion Energy Division, ORNL
R. F. Wood
Affiliation:
Solid State Division, Oak Ridge National Laboratory Oak Ridge, TN 37831-6032
D. B. Geohegan
Affiliation:
Solid State Division, Oak Ridge National Laboratory Oak Ridge, TN 37831-6032
J. M. Donato
Affiliation:
Engineering Physics and Mathematics Division, ORNL
K. R. Chen
Affiliation:
Fusion Energy Division, ORNL
A. A. Puretzky
Affiliation:
Solid State Division, Oak Ridge National Laboratory Oak Ridge, TN 37831-6032
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Abstract

Plasma generation through vapor breakdown during ablation of a Si target by nanosecond KrF laser pulses is modeled using 0-dimensional rate equations. although there is some previous work on vapor breakdown by microsecond laser pulses, there have been no successful attempts reported on the same subject by nanosecond laser pulses. This work intends to fill the gap. a kinetic model is developed considering the following factors: (1) temperatures of both electrons and heavy-body particles (ions, neutrals, and excited states of neutrals), (2) absorption mechanisms of the laser energy such as inverse bremstrahlung (IB) processes and photoionization of excited states, (3) ionization acceleration mechanisms that include electron-impact excitation of ground state neutrals, electron-impact ionization of excited states of neutrals, photoionization of excited states of neutrals, and all necessary reverse processes. the rates of various processes considered are calculated using a second order predictor-corrector numerical scheme. the rate equations are solved for five quantities, namely, densities of electrons, neutrals, and excited states of neutrals, and the temperatures of electrons and heavy-body particles. the total breakdown times (sum of evaporation time and vapor breakdown time) at different energy fluences are then calculated. the results are compared with experimental observations of Si target ablation using a KrF laser.

Type
Research Article
Copyright
Copyright © Materials Research Society 1995

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References

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