激光诱导水击穿阈值的数值分析

【作者】 朱微；

【导师】 陆建；

【作者基本信息】 南京理工大学 ， 等离子体物理， 2010， 硕士

【摘要】 本文针对激光诱导水击穿阈值的计算,从理论上研究了激光与液体物质相互作用过程中的击穿模型,并建立了两种不同的计算模型,在此基础上对击穿辐射阈值做了理论计算,对计算结果进行了分析及与前人的实验结果进行了比较。根据对激光与液体介质相互作用引起光学击穿的机制的分析,在此基础上建立了一级模型,得到了三种光学击穿阈值,并对实际阈值的确定进行了分析。同时在自由电子速率方程的基础上建立了另一种模型,并根据多光子电离和雪崩电离的形成条件以及作用对自由电子速率方程进行了适当的简化,然后通过自由电子密度速率方程的数值解的计算来确定水的激光光学击穿阈值。对两种模型所计算出来的理论结果与实验所测得的结果进行了比较,从而比较了两模型的优点与缺陷,同时发现其结果与波长为可见光和近红外波段,脉宽为纳秒级、皮秒级和飞秒级的脉冲对水的击穿阈值的实验结果相当吻合。将通过一级模型得到的理论计算结果与不同波段、不同脉宽的激光脉冲在纯净的水和含有杂质的水中的实验测量的击穿阈值进行了比较,从而从理论和实验两方面对光致水击穿的辐射阈值的脉宽依赖性、杂质依赖性和光斑尺寸依赖性进行了详细地讨论。更多还原

【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.更多还原