Precision Lamb-shift polarimeter for polarized atomic and ion beams

The Lamb-shift polarimeter described here enables the polarization of a beam of hydrogen (deuterium) atoms, or of a slow proton (deuteron) beam, to be measured with an absolute precision better than 1% within a few seconds. The polarimeter measures the intensity ratios of Lyman-α transitions after Stark quenching of metastable hyperfine substates that were selected in a spin filter. For that purpose the hydrogen (deuterium) atoms are ionized in a Glavish-type ionizer. By charge exchange of the protons (deuterons) in cesium vapor, atoms in the metastable 2S state are produced. For a hydrogen beam of 3x1016 atoms/s, ∼3x106 photons/s are registered in a photomultiplier, i.e., the polarimeter efficiency is about 10-10. The signal-to-background ratio in the Lyman-α spectrum is excellent, thus beam intensities of one to two orders of magnitude less would still be sufficient to carry out a precise measurement. The different components of the polarimeter affect the measured polarization in several ways. It was, therefore, crucial to determine precisely the associated correction factors in order to derive the nuclear polarization from the measured Lyman-α spectra