Highly Polarized Photocathodes Via Minimization of Spin Relaxation

79431S Negative-electron-affinity (NEA) photocathodes, which produce polarized electrons, are a vital component of electron accelerators. The Next Linear Collider (NLC) will require a polarized electron beam intensity at least 20 times greater than that which can be produced with strained GaAs, which is used in the current generation of photocathodes. In addition, the degree of electron polarization will need to be increased beyond the 75% that is currently attainable. This project will develop a new generation of photocathodes capable of yielding intense, highly polarized electron beams for use in advanced electron colliders. In previous work, a strained-superlattice, formed from alternating layers of GaAs and GaAsP, was used to achieve polarization greater than 85%. In this project, a similar strained superlattice concept will be applied to a novel material system, which should overcome material limitations of the GaAs/GaAsP alloys. In Phase I, molecular beam epitaxy will be used to fabricate a strained superlattice structure with alloys other than GaAsP. Growth conditions needed to optimize the desired alloy composition and interface quality will be determined. Photocathode structures will then be fabricated, and their polarization and quantum efficiency will be measured. Commercial Applications and Other Benefits as described by the awardee: A highly efficient, polarized electron source should find use in experimental research at SLAC and other electron collider facilities. These devices also should have applications in such areas as magnetic imaging research, surface analysis, quantum computing, and cryptography.