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

Document Type

Article

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.