On the spin-quantization-axis selection for the spin polarization modeling during laser-electron collision

Spin polarized electron beams have wide applications in high energy physics. The generation of such electron beams has recently attracted considerable attention where the collision of intense laser pulses with high energy electron beams is proposed as one of the potential methods. In previous numerical studies, different spin-quantization axes (SQA) are used, which lead to different calculation results in some configurations of laser interaction with an electron beam. To be consistent with the well-known Thomas-Bargmann-Michel-Telegdi (TBMT) equation, we have proposed a new SQA which is along the TBMT precession direction. We clearly show the difference among the three kinds of SQA selections by comparing the temporal evolution of the electron beam's polarization during the perpendicular collision of an electron beam with s-polarized two-color laser pulses, where the magnetic fields have a parallel component along the electron motion direction. Calculation shows that such differences could be experimentally measured by nowadays facilities. To get the maximum electron polarization degree in the two-color laser pulses based schemes, we also find the optimized condition for the two-color laser parameters. Our studies give a better understanding of spin-polarization calculation and will be beneficial for future experimental designs for electron polarization manipulation.