AN ELECTRON SPIN POLARIZED HELIUM-EXCITED(TRIPLET-2S) METASTABLE BEAM FOR USE IN SURFACE STUDIES

[摘要] A source of electron spin polarized He*(2(;;3)S) metastable atoms is described that provides a thermal energy beam with a flux up to 8 x 10(;;12) metastables/sec/sterad at a polarization P(,z) (TURN) 50%. The polarization is created by optical pumping and can be simply reversed or modulated without changing the beam trajectory or flux. The source is housed in a system of three differentially pumped vacuum chambers which allows the beam to be used for surface experiments in an ultra high vacuum environment. The polarization is measured with a Stern-Gerlach type analyzer which also serves as a useful diagnostic of beam composition and verifies the purity of the 2(;;3)S beam. The beam is demonstrated not to contain any significant admixture of 2(;;1)S metastables, ions, fast neutrals, or photons. Unless care is exercised, however, it is possible to produce a beam of energetic ground state helium which is of much greater intensity than the metastable beam. The conditions under which this occurs are described. A brief overview of metastable deexcitation spectroscopy (MDS) is given and a proposed first experiment involving the investigation of surface magnetism of Ni(110) and the necessary apparatus for this experiment are described.

[发布机构] Rice University