Polarization Effects In The Strong-Field QED Regime

Owing to the rapid development of intense laser technology,a number of PW and10 PW-class lasers worldwide have been completed or under construction.In addition,several 100 PW-class lasers are also planned.These high-power lasers can reach inten-sities of 10^21-24W/cm²after being tightly focused.In such a strong laser field,the field strength that electrons experience in their boosted frames can exceed the Schwinger limit field strength,thus entering the strong-field quantum electrodynamics（QED）dominated regime.In the strong-field QED regime,photons and electron-positron pairs can be gen-erated efficiently.These particle sources are several orders of magnitude brighter or more productive than conventional methods and will play an important role in funda-mental science or applications.Over the last decades,the strong-field QED processes have been studied in detail,and many schemes of generating high-quantitybeams or positrons have also been proposed.However,the electron-positron spin and photon po-larization effects have often been neglected in these studies.Their effects on photon emission and pair production are still unknown.In addition,electrons or positrons with a particular spin polarization exhibit unique properties that have important applications in high-energy physics,materials physics,and astrophysics.How to generate polarized electrons or positrons is also the subject of our research.In this thesis,we have implemented electron-positron spin and photon polarization effects into single-particle code and also QED Particle-In-Cell（PIC）code,to numer-ically investigate how to generate spin-polarized electrons or positrons,and explore these polarization effects on laser-plasma interactions.This thesis mainly consists of four parts as follows.1.In Chapter 3,we propose to generate the polarized electron beam by colliding a two-color linearly polarized laser with a high-energy electron beam.With a specific phase difference between fundamental and second harmonics,the positive and negative cycles of the two-color laser field could have different intensities.After the photon emission,electron spins will flip along one direction overall,so the electron polarization can be realized.2.In Chapter 4,we propose a scheme to produce polarized positrons by the colli-sion of two high-energy electron beams.A high-density driving electron beam provides a strong self-generated electromagnetic field,and another high-energy seeding electron beam experiences the strong field to trigger QED processes.When the impact parame-ter of two beams is nonzero,the field experienced by the seed beam is unipolar,leading to the positron polarization.3.In Chapter 5,we find that dense polarized positrons can be generated by irradiat-ing a 100 PW-class linearly polarized laser onto a foil target.When there is a preplasma withμm-scale-length on the target front,positrons are mainly generated near the skin layer.The generated positrons then experience a subcycle and asymmetric laser field.Under the combined action of radiative polarization and radiation reaction,positrons with opposite polarizations are deflected in opposite directions.Thus,dense polarized positrons can be obtained.4.In Chapter 6,we investigate the polarization effects on intense laser-plasma in-teractions.In the interaction between two 10 PW-class linearly polarized lasers and a foil target,when the electron-positron spin and photon polarization effects are considered,the positron yield will be reduced by 10%and the total laser absorption will be reduced by 5%.The decrease of positron yield is mainly attributed to the fact that the emittedphotons are highly linearly polarized,and have a lower probability of annihilating into electron-positron pairs.