title: Interdependence of in-cell xenon density and temperature during Rb/129Xe spin-exchange optical pumping using VHG-narrowed laser diode arrays.
abstract: The (129)Xe nuclear spin polarization (P(Xe)) that can be achieved via spin-exchange optical pumping (SEOP) is typically limited at high in-cell xenon densities ([Xe](cell)), due primarily to corresponding reductions in the alkali metal electron spin polarization (e.g. P(Rb)) caused by increased non-spin-conserving Rb-Xe collisions. While demonstrating the utility of volume holographic grating (VHG)-narrowed lasers for Rb/(129)Xe SEOP, we recently reported [P. Nikolaou et al., JMR 197 (2009) 249] an anomalous dependence of the observed P(Xe) on the in-cell xenon partial pressure (p(Xe)), wherein P(Xe) values were abnormally low at decreased p(Xe), peaked at moderate p(Xe) (~300 torr), and remained surprisingly elevated at relatively high p(Xe) values (>1000 torr). Using in situ low-field (129)Xe NMR, it is shown that the above effects result from an unexpected, inverse relationship between the xenon partial pressure and the optimal cell temperature (T(OPT)) for Rb/(129)Xe SEOP. This interdependence appears to result directly from changes in the efficiency of one or more components of the Rb/(129)Xe SEOP process, and can be exploited to achieve improved P(Xe) with relatively high xenon densities measured at high field (including averaged P(Xe) values of ~52%, ~31%, ~22%, and ~11% at 50, 300, 500, and 2000 torr, respectively).
authors.affiliation: Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, IL 62901, USA.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Whiting
authors.forename: Panayiotis
authors.initials: P
authors.lastname: Nikolaou
authors.forename: Neil A
authors.initials: NA
authors.lastname: Eschmann
authors.forename: Boyd M
authors.initials: BM
authors.lastname: Goodson
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Barlow
mesh_terms: D000465:Algorithms; D004574:Electromagnetic Fields; D007834:Lasers; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods; D012413:Rubidium / Q000737:chemistry*; D013696:Temperature; D014978:Xenon / Q000737:chemistry*; D014979:Xenon Isotopes
chemical_list: D014979:Xenon Isotopes; D014978:Xenon; D012413:Rubidium