Research On Electron-positron Pair Production Process In Ultra Intense Laser Fields

Since 1887s,the photoelectric effect is found,the interaction of light with matter has become a hot issue in the research of the physics problem.Since 1960s,the first laser device invented,the laser intensity is improving more and more stronger.Especially in the recent 20 years,with the invention of the chirp pulse amplification?CPA?technology,the laser intensity raised eight orders of magnitude.However,the quantum perturbation theory will not valid as the laser intensity increasing so high that some more complex phenomena appearing,such as the pair production process correlated to the multi-photon process.Also,the quantum electrodynamics?QED?can be realized in the laboratory.At present,the laser intensity more than 10²²W/cm²is implemented,and the relevant theoretical and experimental research are put forward to higher challenge of nonlinear QED.In the view of quantum field theory,the so-called vacuum is unstable:under the action of a strong external electromagnetic field,the vacuum may decay with emit electron-positron pairs.In this thesis,we will introduce the QED and some concepts on pair production in strong electromagnetic field.Based on Schwinger mechanism,we give the theoretical method and model,we use the method in pair production process by strong oscillated electric fields with different intensities,different single-frequency fields,and the multi-frequency fields respec-tively,we also generalize our research to the incommensurate field.Firstly,the pair production process in Gaussian laser pulse is studied.The results show two most important features:?1?There are obvious oscillated structures in the particle yield curves and the evident resonance peaks at some particular frequency positions.?2?the one-particle distribution vanishes at zero momentum region when the photon number is even.At last,roles of the laser pulse are discussed,and the main function distributions of some special frequency positions are analyzed in detail.Secondly,the frequency shift and sub-band effect are introduced.We mainly focus on the condition that the external field is closed adiabatically.Results show that the frequency shift and sub-band effect in the pair production can be influenced by system parameters,such as the pulse duration,photon number,and the strength of external field.The frequency shift becomes evident as increases of photon number and the external field strength.And the sub-band width is relatively lower at longer pulse duration,higher photon number region,and weaker external field.Then,the pair-production in the double frequency field and the triple frequency field are studied.Oscillating signatures of the particle yield and the odd-even structure of the momentum-frequency spectrum are described.The roles of the phase factor and the frequen-cy multiplication are analyzed in detail.Results show that there are both oscillating structures and evident resonance peaks for different frequency multiplication,which correlated to the multi-photon process.And the phase factor affect the strength of electric field mainly,the triple frequency field remains the odd-even structures and the double frequency field not.In the end,influences of external parameters are shown,such as the phase factor and the multiple frequency.Finally,we generalize our research to the pair-production in oscillating electric field with incommensurate frequency field.Particle yields of three different fields are studied and the nonlinear effects are found.The particle distribution function of the incommensurate frequency field are shown and the roles of external field on the particle distribution function and peak distribution are analyzed in detail.For relation of the height of peaks and the field strength,an exponential law is given for the coherent incommensurate field.