Precise and ultra-stable laser polarization control for polarized electron beam generation

Polarized Electron Beam is generated by circularly polarized laser light from a GaAsP photocathode with its polarization state determined by the laser light’s polarization- We propose a highly-accurate and ultra-stable circular laser beam polarization flipping system which is consisted of an Electro-optic modulator based on a transversely modulated and birefringence compensated potassium di-deuterium phosphate (DKDP) crystal, driven by an innovative high voltage switching driver- The system performance can be further improved by stabilizing the temperature of the modulator cell and controlling the beam size by a beam condenser /expander pair- We also propose a method which can accurately measure the ellipticity of the output beam without altering the beam’s polarization state- It will make possible an automatically biased and stabilized system with real time feedback of the output beam’s polarization state- Our approaches are aimed to meet the goal of 29(e) of realizing faster helicity flipping and minimize helicity-correlated change-