Two Novel Approaches for Electron Beam Polarization from Unstrained GaAs

Authors

James L. McCarter, University of VirginiaFollow
Nathan B. Clayburn, University of Nebraska - LincolnFollow
J. M. Dreiling, University of Nebraska-LincolnFollow
Timothy J. Gay, University of Nebraska - LincolnFollow
Dominic M. Ryan, University of Nebraska-Lincoln
John Hansknecht, Thomas Jefferson National Accelerator FacilityFollow
Matt Poelker, Thomas Jefferson National Accelerator FacilityFollow
Andrei Afanasev, The George Washington UniversityFollow
Ara Kechiantz, The George Washington University

Date of this Version

2013

Citation

XVth International Workshop on Polarized Sources, Targets, and Polarimetry September 9-13, 2013 Charlottesville, Virginia, USA. PoS(PSTP 2013)060

Abstract

Two novel approaches to producing highly-polarized electron beams from unstrained GaAs were tested using a micro-Mott polarimeter. Based on a suggestion by Nakanishi [1]], twophoton photoemission with 1560 nm light was used with photocathodes of varying thickness: 625m, 0.32m, and 0.18m. For each of these photocathodes, the degree of spin polarization of the photoemitted beam was less than 50%. Polarization via two-photon absorption was highest from the thinnest photocathode sample and close to that obtained from one-photon absorption (using 778 nm light), with values 40.3±1.0% and 42.6±1.0%, respectively. The second attempt to produce highly-polarized electrons used one-photon emission with 778 nm light in Laguerre-Gaussian modes with different amounts of orbital angular momentum. The degree of electron spin polarization was consistent with zero, with an upper limit of ~3% for light with up to ±5ħ of orbital angular momentum. In contrast, the degree of spin polarization was 32.3±1.4% using circularly-polarized laser light at the same wavelength, which is typical for thick, unstrained GaAs photocathodes.