Spatio-temporal Resolved Study Of Transient Electric Field Associated With Laser Plasmas

More and more researchers put their passion into the research of laser plasmas as the development of high-intensity laser.Laser plasmas also play an important role in high energy density physics,including particle accelerate,inertial confinement fusion,astrophysics.Its dynamics is involved in the evolution of laser-induced or self-induced eleconmagnetic field,which is helpful to understand the energy transfer and the den-sity distribution in laser plasmas.Based on the development of diagnostic techniques,this thesis proposed a new method to diagnose the evolution of laser plasmas,with ul-trashort electrons as probes,which is sensitive to electromagnetic field.Utilizing this method(named as ESR,electric schlieren radiography),we realized experimentally to study the transient electric fields(TEFs)generated by the interaction between laser and matter,and reveal its evolutions and structures.Two parts are arranged in this thesis.The proposition of ESR is arranged in the first part.After analyzing the goodness of the main methods used in the diagnostics of laser plasmas,we derived the ESR by modifying the electron shadowgraph,according with the method of light shadowgraph.The second part focused on the application of ESR in experiment.The structure of separated-charged field was observed above the surface of Alumina foil for the first time directly.Then we got the evolution of the TEF and charge distribution by improving the technique of ESR.Meanwhile the characteristic parameters were achieved from the experiment.Firstly,in the first paragraph,pump-probe technique was introduced to realize the time resolution in the background.The key points or difficulties in laser-matter inter-action were described,which were also the focus points in the area of high-field physics or high-energy physics.The corresponding methods of diagnose are proposed or im-proved as the study of the related phenomenon.The speciality of the multiple active methods are analyzed to diagnose different situations where our method is potential to be applied.Secondly,the principle of ESR was explained in this part.In second paragraph,light shadowgraph which has studied over a century was induced to detect the density of laser plasmas.Based on the light shadowgraph,it is found that the electrons obey the similar function as light,when electrons go through electric field.Meanwhile,this property is also suitable to the charged particle like protons.Electrons have the ad-vantages as easier to achieve,modify and inexpensive cost.In third paragraph,the key point is that calculating the results by extracting the information from the images which involved in some physical process.In this paragraph,the arithmetic of abel inversion was realized by Matlab codes automatically considering the decrease of signal noise,the increase efficient of interactive calculation.We set up the experiment to realize the ESR technically in the fourth paragraph.To realize the prospective time resolution and spatial resolution,the whole system were designed in details including the laser and light path,the electron gun,the modulator of target scheme,the amplifier,the detector and so on.Thirdly,Two experiments were carried out to study the laser plasmas in the sec-ond paragraph.By insert grid to modify the picosecond electron beam,the spatial resolution of 80 ?m and temporal resolution of 3.7 ps were achieved to study the laser initiated the 2?m foil.The electric structure above the surface of target at delay time 25 ps were calculated from this experiment.The separated charge formed by the emitted hot electrons and the positive charge in the target presented the,"peak-valley" structure in the normal direction.The intense profile of TEFs was like a volcano,which is the first time to detect the feature.Based on that,inclined holes were employed in the sixth paragraph by improving the spatial resolution.The evolutions of TEF were shown to reveal the velocity and numbers of emitted electrons.The transverse expand of the hot emitted electrons resulted in the decrease of deflection of electron beamlets as the time delay increase.At last,the practicability of ESR was proved by the realization of experiments,and parameters of laser plasmas were achieved at the same time.In theory,ESR can be scaled to apply in high electromagnetic fields,and provides a useful tool in high energy dense physics.