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Numerical analysis of laser-induced water breakdown threshold

Author: ZhuWei
Tutor: LuJian
School: Nanjing University of Technology and Engineering
Course: Plasma Physics
Keywords: breakdown threshold pulsewidth water impurity spot size avalanche ionization multiphoton ionization
CLC: TN249
Type: Master's thesis
Year: 2010
Downloads: 70
Quote: 0
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Abstract


In this paper, in order to calculate the breakdown thresholds, the physical mechanism of optical breakdown induced by laser in aqueous media is analyzed and two breakdown models are built. Using these models, the breakdown thresholds are calculated in theory. Besides these values are analyzed and compared to the experimental data the researchers have given.According to the analysis of the mechanisms of laser induced breakdown (LIB) in aqueous liquids, the first-order model is established, and then three kinds of breakdown thresholds is obtained. In addition, the selection of practical threshold is discussed. Another model based on the rate equation formalism for free electron generation is established. As the formative conditions of multiphoton ionization and avalanche ionization, the rate equation formalism is simplified reasonably. And then the breakdown thresholds are obtained by calculating the numerical value of the rate equation formalism of free electron density generation. Comparing these results with the values gained through the previous experiments, the merits and defects of the two models are proposed. In addition, these results are comparatively corresponded with the measured threshold for visible and near-infrared pulse LIB with nanosecond, picosecond and femtosecond pulsewidths regimes.Comparing the calculating values through the first order model with the measured thresholds with various wavelengths and various pulsewidths both in pure and impure water, pulsewidth and impurity dependence, wavelength dependence and the spot size dependence of the LIB threshold are discussed in theory and experiment.

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