Research On Weakly Electriferous Effects Of Laser Plasma Based On The Probe-target Method

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.