Experimental Study On GaAs Spin-polarized Electron Source And Optical Electron Polarimeter

High quality spin-polarized electron beam is the key for the experimental investigation of spin-resolved effect in the areas of atomic and molecular physics, life sciences, solid surface physics, material sciences, high energy and nuclear physics etc. Compared with other electron source, the GaAs spin-polarized electron source developed the late 1970s has been widely used because of its high polarization, narrow energy spread, high brightness, stable intensity, long lifetime, compactness and the easiness of changing polarization direction. Thus the electron beam produced by GaAs spin-polarized electron source has become the most useful detection method associated with the spin-resolved effect experiments.Because of its complicated experimental requirements and difficult techniques, only a few groups in the world develop the GaAs spin-polarized electron source and perform the spin-resolved effect experiments. A GaAs spin-polarized electron source with highly stable polarized beam and long lifetime has been developed successfully in China firstly by our group after several years of tough experiment. The electron beam produced by this spin-polarized source can be kept between 9.20μA and 9.80μA for 1500h without any breaking, and the result is more better than that obtained by other groups (500h⁶00h).During the development of GaAs spin-polarized electron source, much of the difficult techniques have been solved, including stable and stringent ultrahigh vacuum circumstance (¹Ã—10^-8Pa), super clean surface of GaAs crystal, achievement of small amount of cesium and oxygen with high purity of 99.99%, effective negative electron affinity to emit the polarized electrons from GaAs surface, electron optical system for the long distance transmitting of the low energy electron beam, and the complicated magnetic field shielding system. From many times of experiments, not only have we firstly obtained the comparison data of different activation processes, but also we conclude that, besides the important parameters and the rigorous controlling procedure being studied more carefully, the most important thing is that the stringent activation process should be performed for several times to achieve the polarized electron beam with extremely stability and longtime. Some important experimental data have beenacquired for the future research work.Furthermore, the optical electron polarimeter based on the Stokes parameter measurement also has been developed in this dissertation. It will be used to measure the polarization of the current beam emitted from GaAs polarized electron source and perform the spin-resolved effects research later. We have finished all the parts of the optical electron polarimeter, including the analysis system for the Stokes parameters of radiation fluorescence, photon detection system, and electronic system etc. From the experimental controlling system and data acquisition and processing software system, the fully experimental processes can be performed automatically by computer. The multi-variable linear fitting method with statistic error analyze is used firstly by our group for the data acquisition and processing during the polarization measurement, which is a little difference from that used in other groups. Finally, the Stokes parameter of Pi=0.920, P2=0.020 and P3=0.012 for linear polarized weak light is measured, and the data agrees very well with the theoretical prediction. This measurement assures that our optical electron polarimeter and the multi-variable linear fitting method can work very well for the future experiments.