【作者】 纪运景；

【导师】 陆建； 卞保民；

【作者基本信息】 南京理工大学 ， 测试计量技术及仪器， 2009， 博士

【摘要】 强激光与物质相互作用过程中表现出来的电学效应包含了激光等离子体演变过程丰富的特征信息,对这种电学效应进行测试和分析已经逐渐发展成为研究激光等离子体特性参数的重要手段之一。本文针对1064nm波长、功率密度约10~10W／cm~2的脉冲激光与金属靶作用过程中等离子体的弱荷电效应,从理论和实验两个方面进行了深入系统的研究,初步建立了一个弱荷电球为基础的激光等离子体扩散模型。论文根据对点源激光等离子体冲击波演化过程中能量分布特征的分析,提出了激光等离子体形成初期具有内部荷电储能的新观点,这种微弱荷电效应源于脉冲激光烧蚀靶材期间少量高速电子的逃逸,从而构成了初期的弱荷电等离子体球。从高温高压激光等离子体荷电量少、膨胀迅速的基本特征出发,详细分析荷电等离子体演变过程中的电学特性,以及对外表现出来的电学效应,同时深入研究了金属靶与荷电等离子体之间的相互作用机理,以激光作用过程和等离子体膨胀过程的时间特征为基础,建立激光等离子体荷电效应等效电流源模型。通过对等效电流源演变对金属靶电势信号影响的分析,将等离子体荷电接触效应、等离子体扩散机制、电场感应机制、净余电荷转移机制,与激光参数、材料特性等参数进行综合性分析,提出“靶探针”测试激光等离子体荷电的新方法,建立了测试信号分析模型。并设计了激光等离子体弱荷电效应的“靶探针”测试装置,对自由靶、控制靶两种情况下的靶电势信号演变规律进行了一系列实验,研究激光作用能量、靶材特性参数、偏置电压等因素对激光等离子体微弱荷电效应的影响。实验研究结果表明,本论文建立的激光等离子体弱荷电效应模型与靶电势信号的演变规律完全吻合。该实验装置还能够对激光等离子体中存在的净余电荷量进行了估测。本论文的研究成果提供了一种新的激光等离子体电学效应的测试方法,丰富了激光等离子体理论与实验基础,为激光等离子体诊断提供了很有价值的参考。更多还原

【Abstract】 Abundant evolvement information of laser plasma is manifested by the electrical effect during the process of the interaction between high power laser and matter. The technique for testing and analyzing the electrical effect for laser plasma has become one of the most important methods for plasma diagnosis. The electrical effect derived from the interaction between the pulsed laser (wavelength:1064 nm; intensity near 1011 W/cm2) and the metal target is investigated theoretically and experimentally, and a diffusion model based on a low electriferous sphere for laser plasma is established primarily.According to analyzing the energy distribution in the evolved stage of a point-source laser plasma shock wave, a new viewpoint is proposed that the energy is stored by inner charged particles in the initial stage of the laser plasma’s formation. The feebly electrical effect is rooted in the fact of the escape of a few high-speed electrons which forms a plasma sphere with low charge when laser ablating metal target. Considering the characters of low charge and rapid bulge for the high temperature and pressure laser plasma, the electrical characteristic of the charged plasma in the process of evolution and the electrical effect to external are analyzed in detail.At the same time, mechanism of the interaction between metal target and charged laser plasma is also profoundly studied. An equivalent current supply model is founded for the electric field effect of laser plasma on the basis of interaction process and the time character of the laser plasma’s expansion process.The electrical potential signals of the metal targets affected by the evolvement of the equivalent current supply are also analyzed. In the integrated analysis, the mechanisms of electric induction, diffusion and surplus charge’s transfer are all considered, as well as the parameters of laser and the characters of material.A new target-probe method of testing the electric effect for laser plasma is proposed and the analysis model for testing signal is established. A target-probe experimental device is designed for detecting the feebly electrical effect of laser plasma. A series of experiments are implemented to explore the evolvement rule of electricity signal for free and controlled targets respectively. The impacts of the incident energy of laser, special parameters of targets and offset voltage on the feebly electrical effect of the laser plasma are investigated. The results indicate that the feebly electrical effect established in this dissertation coincides with the experimental results. Besides, the device also can be used to measure the remained electric charge in laser plasma.In conclusion, the results of this dissertation will provide a novel testing method for the electrical effect of laser plasma, enrich the theoretical and experimental basis for laser plasma and provide valuable references for the diagnosis of laser plasma.更多还原