arXiv subjects

D. -A. Luh

Publications and source records attributed to D. -A. Luh.

6 recordsLinked to original sources

arXiv2005

Strain-Compensated AlInGaAs-GaAsP Superlattices for Highly-Polarized Electron Emission

Spin-polarized electron emission from the first superlattice photocathodes developed with strain compensation is investigated. An opposite strain in the quantum well and barrier layers is complished using an InAlGaAs/GaAsP superlattice structure. The measured values of maximum polarization and quantum yield for the structure with a 0.18 um-thick working layer are close to the best results reported for any strained superlattice photocathode structure, demonstrating the high potential of strain compensation for future photocathode applications. An analysis of the photoemission spectra is used to estimate the parameters responsible for the polarization losses.

cond-mat.other↗

arXiv2004

Polarized Electrons for Linear Colliders

Future electron-positron linear colliders require a highly polarized electron beam with a pulse structure that depends primarily on whether the acceleration utilizes warm or superconducting rf structures. The International Linear Collider (ILC) will use cold structures for the main linac. It is shown that a dc-biased polarized photoelectron source such as successfully used for the SLC can meet the charge requirements for the ILC micropulse with a polarization approaching 90%.

physics.acc-ph↗

arXiv2004

A systematic study of polarized electron emission from strained GaAs/GaAsP superlattice photocathodes

Spin-polarized electron photoemission has been studied for GaAs/GaAs$_{1-x}$P$_x$ strained superlattice cathodes grown by gas-source molecular beam epitaxy. The superlattice structural parameters are systematically varied to optimize the photoemission characteristics. The heavy-hole and light-hole transitions are reproducibly observed in quantum efficiency spectra, enabling direct measurement of the band energies and the energy splitting. Electron-spin polarization as high as 86% with over 1% quantum efficiency has been observed.

physics.ins-det↗

arXiv2004

Atomic Hydrogen Cleaning of Polarized GaAs Photocathodes

Atomic hydrogen cleaning followed by heat cleaning at 450$^\circ$C was used to prepare negative-electron-affinity GaAs photocathodes. When hydrogen ions were eliminated, quantum efficiencies of 15% were obtained for bulk GaAs cathodes, higher than the results obtained using conventional 600$^\circ$C heat cleaning. The low-temperature cleaning technique was successfully applied to thin, strained GaAs cathodes used for producing highly polarized electrons. No depolarization was observed even when the optimum cleaning time of about 30 seconds was extended by a factor of 100.

physics.ins-det↗

arXiv2004

Recent Progress at SLAC Extracting High Charge from Highly-Polarized Photocathodes for Future-Collider Applications

Future colliders such as NLC and JLC will require a highly-polarized macropulse with charge that is more than an order of magnitude beyond that which could be produced for the SLC. The maximum charge from the SLC uniformly-doped GaAs photocathode was limited by the surface charge limit (SCL). The SCL effect can be overcome by using an extremely high (>1019 cm-3) surface dopant concentration. When combined with a medium dopant concentration in the majority of the active layer (to avoid depolarization), the surface concentration has been found to degrade during normal heat cleaning (1 hour at 600 C). The Be dopant as typically used in an MBE-grown superlattice cathode is especially susceptible to this effect compared to Zn or C dopant. Some relief can be found by lowering the cleaning temperature, but the long-term general solution appears to be atomic hydrogen cleaning.

physics.acc-ph↗

arXiv2002

The SLAC Polarized Electron Source

The SLAC PES, developed in the early 1990s for the SLC, has been in continuous use since 1992, during which time it has undergone numerous upgrades. The upgrades include improved cathodes with their matching laser systems, modified activation techniques and better diagnostics. The source itself and its performance with these upgrades will be described with special attention given to recent high-intensity long-pulse operation for the E-158 fixed-target parity-violating experiment.

physics.acc-ph↗