A derivative standard for polarimeter calibration

Abstract

A long-standing problem in polarized electron physics is the lack of a traceable standard for calibrating electron spin polarimeter. While several polarimeter are absolutely calibrated to better than 2%, the typical instrument has an inherent accuracy no better than 10%. This variability among polarimeter makes it difficult to compare advances in polarized electron sources between laboratories. We have undertaken an effort to establish 100 nm thick molecular beam epitaxy grown GaAs(110) as a material which may be used as a derivative standard for calibrating systems possessing a solid state polarized electron source. The near-bandgap spin polarization of photoelectrons emitted from this material has been characterized for a variety of conditions and several laboratories which possess well calibrated polarimeter have measured the photoelectron polarization of cathodes cut from a common wafer. Despite instrumentation differences, the spread in the measurements is sufficiently small that this material may be used as a derivative calibration standard.Presented at the 16th IEEE Particle Accelerator Conference (PAC 95) ABSTRACTA long-standing problem in polarized electron physics is the lack of a traceable standard for calibrating electron spin polarimeter. While several polarimeter are absolutely calibrated to better than 2%, the typical instrument has an inherent accuracy no better than 10%. This variability among polarimeter makes it difficult to compare advances in polarized electron sources between laboratories. We have undertaken an effort to establish 100 nm thick molecular beam epitaxy grown GaAs(110) as a material which may be used as a derivative standard for calibrating systems possessing a solid state polarized electron source. The near-bandgap spin polarization of photoelectrons emitted from this material has been characterized for a variety of conditions and several laboratories which possess well calibrated polarimeter have measured the photoelectron polarization of cathodes cut from a common wafer. Despite instrumentation differences, the spread in the measurements is sufficiently small that this material may be used as a derivative calibration standard.

Precision electroweak measurements on the Z resonance

“…The perils of employing a less reliable method to test a precision device were apparent when large corrections for atomic electron momentum effects in the Møller target were discovered [100], after which, good agreement was obtained. In addition, a less direct comparison was provided by Mott polarimeter bench tests of the GaAs photocathodes [101].…”

Spin-Resolved Valence Photoemission

“…Measured with JLAB 5 MeV Mott polarimeter, S eff À0.4008, which was calibrated by thickness extrapolation to zero foil thickness Grames et al [47] McCarter et al [55] 42.69 AE 0. 92 100 nm film of GaAs (110) in purpose built polarized electron source Measured using a 120 kV Mott polarimeter Mulhollan et al [293] À83 AE 5 Photoemission from Fe (110) on W(110) at E F P value refers back to Dedkov et al [194] and Kurazawa et al [88], which both then refer back to Raue et al [29] who used a 100 kV Mott polarimeter in which S eff was stated, without further detail, to be 0.16. Kurazawa data show quite a spread in values Dedkov et al [190] 35 AE 5 2 eV 2 y electrons from Co grown on Cu(001) P value refers back to Kisker et al [294] in which a classical Mott polarimeter operating at 100 kV was used Winkelmann et al [64] 8.2 AE 0.5 2 eV 2 y electrons from Ni (110) P value refers back to Hopster et al [295] in which a classical Mott polarimeter operating at 100 kV and estimated to be correct to 10 % was used Typical instrumental asymmetries for retarding-potential Mott polarimeters are around 10 %, though values much lower than this have been reported.…”

Polarization and charge limit studies of strained GaAs photocathodes

“…A 'standard' source of polarized electrons was instead developed to determine the effective Sherman function. [42] The polarization of the standard source was measured at various institutions which had developed highly accurate, self-calibrating polarimeters. The polarization value for the standard source used in the calibration of the GTL polarimeter was the average of the polarization values at those institutions.…”

“…The polarization of the standard source was also measured by very accurate, self-calibrating polarimeters at various institutions. [42] These measurements on the standard source can help scientists to compare the polarimeter calibrations being used at the various institutions. A graph depicting the typical plot of polarization and QE versus wavelength of illumination for the standard source is shown in Fig.…”