Research On Electron Acceleration,Radiation And Positron Creation Driven By Intense Laser

Thanks to the continuous progress of laser technology,especially the advent of the technology of Chirped Pulse Amplification(CPA),people can product ultra-short and super-strong laser pulse with intensity up to 10²²W/cm²and the pulse duration of tens femtoseconds in the laboratory.This kind of intense femtosecond laser pulse has been an critical factor in the development of high-energy physics,plasma physics and other basic physics fields.When the laser pulse with a peak intensity of 10¹⁸W/cm²inter-acts with plasma,electrons are accelerated to relativistic velocities instantly,leading to the emergence of a lot of strong nonlinear physical phenomena,such as laser relativistic self-focusing,relativistic transparency,nonlinear modulation,laser wake field accelera-tion and high order harmonic generation,etc.During the recent years,there have been a number of laser facilities under construction,aimed at the laser power of 10-100 PW(1 PW=10¹⁵W),corresponding to the peak intensity of 10²³-10²⁴W/cm².Under such high intensities,the interaction of laser and plasma goes into the quantum electrodynam-ics(QED)regime,and electrons are accelerated to extreme relativistic energy,activating some new physical effects like the relativistic randomness,radiation capture/radiation reaction effect,high energy?-photon radiation,e⁺e^-pair creation and QED cascade.The extreme intense laser-plasma interactions bring new opportunities and challenges for physics research.In the first two chapters of this paper,the basic physical principles and QED effects of laser-plasma interaction are reviewed,and the physical process and basic configuration of generating high-energy?-photon radiation and electron-positron pairs plasmas are described respectively.In the next two chapters,we research and demonstrate the QED effects in intense laser-plasma interaction in detail,like high-energy electron ac-celeration,?radiation,radiation reaction,and e⁺e^-pair creation etc.Among the physical effects,the radiation reation effect is widely discussed by physi-cists.As the laser intensity approaches 10²²W/cm²,the recoil force(radiation reaction force,RR force)from high-energy photons radiated by relativistic electrons becomes im-portant and may be comparable with the ponderomotive force of the laser pulse.As a result,the electron dynamics is modified greatly.In the third chapter,By using particle-in-cell simulations,we theoretically demonstrate that the polarization of laser pulse has sig-nificant influence on the electron behaviors and accompanying radiation in near-critical-density plasmas.Due to the RR force and the pinching effect of the self-generated mag-netic field,it turns out that much more electrons are trapped in the center of a circularly-polarized(CP)laser pulse than that of a linearly-polarized(LP)laser pulse.Meanwhile,the?-photon emission is characterized by a two-peak structure in the LP case,while it is dominated in the forward direction in the CP case where electrons keep moving forward along the laser propagating direction.These may serve as a direct signature for radiation trapping effect in forthcoming experiments to be carried out on 10 petawatt(PW)laser facilities.In addition,the generation of electron-positron pair in ultra-relativistic laser intensity is one of the hot topics in high-energy physics and plasma physics in recent decades.At present,it is an effective method to obtain dense high-energy electron-positron pair plasma by the interaction between super-strong laser and solid target.In the forth chapter,we report the scheme of copious e⁺e^-pairs generated by enhanced electron injection into a mass-limited foil driven by a circularly polarized laser pulse with focused laser intensity of 10²³W/cm².It's shown that the laser pressure pushes the center of the foil forward as a whole,while laser electromagnetic(EM)filed on both sides pass through the boundary of the foil and are reflected by the thick carbon target in front.The accelerated electrons of the mass-limited foil are injected into the hole-boring surface of the carbon target,colliding with the laser reflected from the latter,enhancing of the emission of?-photon by nonlinear Compton scattering.Finally,we obtained 10¹⁴?-photons with the energy over 1 Me V,the average energy is 14.48 Me V and a total energy conversion efficiency from the laser to?-ray is 18%.Meanwhile,a positron beam comprising 10¹¹positrons with an average energy of 160 Me V is generated,and the maximum density is 6n_c(n_cis the critical density),which can be widely used in laboratory astrophysics to carry out relevant experiments in PW laser facilities,and has certain value for future studies on high-energy accelerator physics(such as electron-positron colliding and?-?colliding)and strong-field ultra-fast physics.