Advances in Polarized Electron Sources

In this chapter, we review recent advances in the technology of polarized electron sources. Significant electron-spin polarization above 50% has been achieved with new photocathode structures based on the conventional GaAs photoemitter. Since 1991, significant enhancements of polarization utilizing strained heterostructures and GaAs-A1GaAs superlattices have been reported. We discuss the basic theoretical background and the techniques required to build such strained structures in detail. The operational performance of strained GaAs cathodes now in use at the Stanford Linear Accelerator Center (SLAC) for colliding-beam and fixed-target experiments is reviewed as well.