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Spin polarized photocathodes are key to the future operation of electron accelerators such as the ones at Thomas Jefferson National Accelerator Facility and Brookhaven National Laboratory. Currently, these photocathodes come in short supply due to limited production by molecular beam epitaxy. By developing a process to implement similar structures using metal organic chemical vapor deposition, the availability of these devices can be increased. In this paper, we detail the implementation of recent photocathode advancements via metal organic chemical vapor deposition process and show an improvement in both polarization and quantum efficiency of our devices compared to those fabricated via molecular beam epitaxy, with devices reaching 82% polarization and 2.9% quantum efficiency. [ABSTRACT FROM AUTHOR]

The degree of polarization of photoemitted electrons extracted from bulk unstrained GaAs photocathodes is usually considerably less than the theoretical maximum value of 50%, as a result of depolarization mechanisms that originate within the photocathode material and at the vacuum surface interface. This paper provides a comprehensive review of depolarization mechanisms and presents a systematic experimental evaluation of polarization sensitivities to temperature, dopant density, quantum efficiency, and crystal orientation. The highest measured polarization was ~50%, consistent with the maximum theoretical value, obtained from a photocathode sample with relatively low dopant concentration and cooled to 77 K. In general, measurements indicate electron spin polarization can be enhanced at the expense of photoelectron yield (or quantum efficiency). [ABSTRACT FROM AUTHOR]

Photocathodes were at the heart of quantum physics development in the early twentieth century and are still used in high technology devices like nightvision goggles, photomultiplier tubes, and particle accelerators. The simplest form of the photocathode is ametallic surface, negatively biased, from which electrons are extracted by energetic photons. After a brief description of the photocathode preparation, this chapter will present the latest developments and limitations of metallic and semiconductor photocathodes. [ABSTRACT FROM AUTHOR]

Techniques for nonevaporable getter (NEG) coating a large diameter chamber are presented along with vacuum measurements in the chamber using several pumping configurations, with base pressure as low as 1.56 × 10−12 Torr (N2 equivalent) with only a NEG coating and a small ion pump. The authors then describe modifications to the NEG coating process to coat complex geometry chambers for ultracold atom trap experiments. Surface analysis of NEG coated samples is used to measure the composition and morphology of the thin films. Finally, pressure measurements are compared for two NEG coated polarized electron source chambers: the 130 kV polarized electron source at Jefferson Lab and the upgraded 350 kV polarized electron source, both of which are approaching or within the extreme high vacuum range, defined as P < 7.5 × 10−13 Torr. [ABSTRACT FROM AUTHOR]

This paper presents modeling results of Mie-type GaAs nanopillar array resonant structures and the design of negative electron affinity photocathodes based on Spicer's three-step model. For direct-bandgap GaAs with high intrinsic absorption coefficient in the 500 ∼ 850 nm spectral range, photoelectrons were found to be highly localized inside the nanopillars near the top and side surfaces where electrons can be efficiently transported and emitted into vacuum, and the light reflectance can be reduced to ∼1% level at resonance wavelengths. Predictions of spectrally resolved photoemission indicate that these nanophotonics resonators, when properly optimized, can increase the photo-electron emission quantum efficiency at resonance wavelengths to levels limited only by the surface-electron escape probability, significantly outperforming traditional flat wafer photocathodes. Ultrafast photoelectric response is also expected from these nanostructured photocathodes due to the much shorter photoelectron transport distance in nanopillars compared to flat wafers. Given these unique optoelectronic properties, GaAs nanophotonic resonance structured photocathodes represent a very promising alternative to photocathodes with flat surfaces that are widely used in many applications today.