ADVANCES IN POLARIZED ELECTRON SOURCES

In this chapter, we review recent advances in the technology of polari zed electron sources. Significant electron-spin polarization above 50% has been achieved with new photocathode structures based on the conve ntional GaAs photoemitter. Since 1991, significant enhancements of pol arization utilizing strained heterostructures and GaAs-AlGaAs superlat tices have been reported. We discuss the basic theoretical background and the techniques required to build such strained structures in detai l. 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.