Study On Polarization Effect In Strong Field QED Proces

With the advancement of laser technology,the laser intensity continues to increase,reaching levels of 10²² 10²³W/cm².Within such intensity ranges,the interaction between lasers and matter enters the strong relativistic region,where Quantum Electrody-namics（QED）effects become significant.Nonlinear Compton scattering and nonlinear Breit-Wheeler processes are two of the most extensively studied QED effects.These processes are utilized for generating polarized relativistic particle sources in ultra-strong laser configurations and hold crucial applications in detection of vacuum poalrization.This dissertation primarily focuses on studying electron spin,photon polarization and vacuum polarization effects during these two strong-field QED processes.The specific progress is outlined as follows:1)The effects of photon polarization on the polarization and yield of pairs in QED cascades are investigated.To reveal the polarization characteristics of photons,a Monte Carlo simulation method including photon polarization and positron polarization is developed.The polarization of emitted photons during the interaction between an ultrarelativistic electron beam and a counterpropagating elliptically polarized laser pulse is studied,along with its effect on the polarization and yield of pairs.It is observed that the emitted photons from nonlinear Compton scattering are partially polarized,exerting a significant influence on the subsequently produced pairs.This results in a 35%reduction in positron polarization and a 13%reduction in yield compared to the scenario where the photons are unpolarized.These findings underscore the pivotal role of photon polarization in QED and emphasize the necessity of considering the photon polarization for accurately predicting QED polarization effects.2)The angular spread at emission in nonlinear Compton scattering is investigated.We derive the angle-resolved radiation probability in strong fields and develop a numerical simulation method.The effect of angular spread at emission on the polarization and particle angular distribution of photon emissions and final electrons is explored.It is discovered that the angular spread at emission significantly impacts the angular distribution and polarization of photon emissions and final electrons:the angular distribution widths of electrons and photon emissions increase,and the average polarization of electrons is reduced due to the correction of the radiation reaction force.These findings correct previous studies that neglected angular spread at emission and provide a more accurate theoretical basis for obtaining a high-energy polarized electron（positron）source via intense laser interactions.3)The vacuum polarization effect in strong-field QED is studied.The vacuum po-larization effect in strong-field QED is examined in this study.The impact of vacuum polarization on polarization is analyzed,and the potential for observing the vacuum polarization effect using high-energy probes is discussed.A program module is de-veloped in this thesis,including vacuum dichroism and vacuum birefringence effects,to investigate the collision process of linearly polarized photons with a laser field.The results indicate that,owing to vacuum dichroism and vacuum birefringence effects,the polarization of photons alters as they propagate in a strong background field.Vacuum birefringence leads to a decrease in the remaining photon polarization,while vacuum dichroism causes an increase.These phenomena can serve as photon signals for detecting vacuum birefringence and vacuum dichroism,respectively.