Electron polarimeter based on spin-polarized low-energy electron diffraction

A compact electron polarimeter which operates at low scattering energies (100 eV) has been built and characterized. The polarimeter uses spin-dependent diffraction from a W(001) single crystal to measure the electron spin polarization of an incident electron beam. The design obtains reliable operation by attention to the input optics, the crystal mount, and the alignment procedure. The transport lens delivers the electron beam to the analyzer over an acceleration range of at least 2.0–0.33 while simultaneously keeping the angular convergence of the beam less than ±1.5°, and the magnification constant to within ∼30%. The crystal mount allows both orientation of the crystal normal to within 0.2° and flashes to 2500 K. Geometric instrumental asymmetries are linear in displacement (AD = 4%/mm) and angular displacement (Aθ = 3%/deg) of the sample. The alignment procedure and performance of the polarimeter are illustrated using spin-polarized low-energy electron diffraction rotation curves. Preliminary results suggest that the polarimeter may be operated for 1 h between cleaning cycles without degradation of the figure of merit.