We report a measurement of the ratio of dimensionless enhancement factors ??0 for Cs-129Xe and Rb-129Xe in the temperature range 115???140 ???C; both pairs are used in spin-exchange optical pumping (SEOP) to produce hyperpolarized 129Xe. ??0 characterizes the amplification of the 129Xe magnetization contribution to the alkalimetal electronic effective field, compared to the case of a uniform continuous medium in classical magnetostatics. The measurement was carried out in ???hybrid??? vapor cells containing both Rb and Cs metal in a prescribed ratio, producing approximately the same vapor density for both. Alternating measurements of the optically detected electron paramagnetic resonance (EPR) frequency shifts caused by the SEOP polarization and subsequent sudden destruction of the same quantity of 129Xe magnetization were made for 133Cs and either 87Rb or 85Rb. An important source of systematic error caused by power fluctuations in the pump laser that produced variable light shifts in the EPR frequency was characterized and then mitigated by allowing sufficient warm-up time for the pump laser. We measured (??0)CsXe/(??0)RbXe = 1.215 ?? 0.007 with no apparent temperature dependence. Based on our previous measurement (??0)RbXe = 518 ?? 8, we determine (??0)CsXe = 629 ?? 10, which is more precise than, but consistent with, a previous measurement made by J. Fang et al. [Chin. Phys. B 23, 063401 (2014)].

The 53rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics will take place from May 30 – June 3, 2022 in Orlando, Fl, USA. Virtual Help Desk

We report a measurement of the ratio of dimensionless enhancement factors κ_0 for Cs-^129Xe and Rb-^129Xe in the temperature range 115-140 ^∘C; both pairs are used in spin-exchange optical pumping (SEOP) to produce hyperpolarized ^129Xe. κ_0 characterizes the amplification of the ^129Xe magnetization contribution to the alkali-metal electronic effective field, compared to the case of a uniform continuous medium in classical magnetostatics. The measurement was carried out in "hybrid" vapor cells containing both Rb and Cs metal in a prescribed ratio, producing approximately the same vapor density for both. Alternating measurements of the optically detected EPR frequency shifts caused by the SEOP polarization and subsequent sudden destruction of the same quantity of ^129Xe magnetization were made for ^133Cs and either ^87Rb or ^85Rb. An important source of systematic error caused by power fluctuations in the pump laser that produced variable light shifts in the EPR frequency was characterized and then mitigated by allowing sufficient warm-up time for the pump laser. We measured (κ_0)_ CsXe/(κ_0)_ RbXe = 1.215 ± 0.007 with no apparent temperature dependence. Based on our previous measurement (κ_0)_ RbXe=518 ± 8, we determine (κ_0)_ CsXe = 629 ± 10, more precise than but consistent with a previous measurement made by another research group.

Z. Xu, et al. [Phys. Rev. A 103, 023114 (2021)], have reported a measurement for the enhancement factor κ, which characterizes the overlap of the electron wavefunction with the noble-gas nucleus in Cs-^129Xe spin-exchange optical pumping (SEOP), that is more than an order of magnitude higher than previous experimental results and theoretical estimates. There is no plausible proposed physical basis for this discrepancy. As the authors repeatedly mischaracterize the nature and properties of the enhancement factor and do not completely describe their experimental technique, there is little reason to accept or consider this result in its current form in the context of future relevant work on Cs-Xe SEOP and its applications.

Received 30 November 2021DOI:https://doi.org/10.1103/PhysRevA.104.069904©2021 American Physical Society

Received 30 July 2021DOI:https://doi.org/10.1103/PhysRevA.104.029904©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFine & hyperfine structureNuclear & electron resonanceOptical pumpingOptics & lasersAtomic, Molecular & Optical

We report a measurement of the dimensionless enhancement factor $\kappa_0$ for the Rb-$^{129}$Xe pair commonly used in spin exchange optical pumping (SEOP) to produce hyperpolarized $^{129}$Xe. $\kappa_0$ characterizes the amplification of the $^{129}$Xe magnetization contribution to the Rb electronic effective field, compared to the case of a uniform continuous medium in classical magnetostatics. The measurement is carried out in Rb vapor cells containing both $^3$He and $^{129}$Xe and relies on the previously measured value of $\kappa_0$ for the Rb-$^3$He pair. The measurement is based on (1) the optically detected (Faraday rotation) frequency shift of the $^{87}$Rb EPR hyperfine spectrum caused by the SEOP nuclear polarization and subsequent sudden destruction of nuclear polarization of both species and (2) a comparison of NMR signals for the two species acquired just prior to the EPR frequency shift measurements. We find $(\kappa_0)_{\rm RbXe} = 518\pm 8$, in good agreement with previous measurements and theoretical estimates but with improved precision.

Submitted for the DAMOP19 Meeting of The American Physical Society Magnetic-field stability in unshielded Helmholtz coils1 DAVID P. MORIN, SHENG ZOU, CHAMITHRI ADIKARIGE, ZAHRA ARMANFARD, TREVOR FOOTE, BRIAN SAAM, Washington State University — Many tabletop AMO experiments require magnetic field stability, e.g., for precise measurement of resonance frequencies and shifts. This is often achieved with a very small or nominally zero field, where the entire apparatus is shielded with several layers of expensive mu-metal. Spin-exchange optical pumping (SEOP), by contrast, practically requires a larger (tens of gauss) field that defines a lab quantization axis and mitigates low-field spin-relaxation effects. We routinely stabilize unshielded Helmholtz coils to better than a part in 105 at 30 G in an ≈ 10 Hz bandwidth, and achieve a few parts in 106 late at night with less external interference [1]. In this work, we compare several stabilization techniques based on driving the inductive load with a commercial (CV/CC) power supply, including: using the supply in current-control mode (worst result); and using it in voltage-control mode coupled with one or more of: (1) a stable sensing resistor in series with the coils, (2) an external comparator driving the gate of a FET in series with the coils, and (3) the output voltage generated by a commercial magnetometer fed directly to the power supply sensing inputs. [1] A. Nahlawi et al., in prep.; see poster by S. Zou et al., at this conference. 1NSF Grant no. PHY-1708048 Brian Saam Washington State University Date submitted: 28 Jan 2019 Electronic form version 1.4

We report a measurement of the ratio of dimensionless enhancement factors $\kappa_0$ for Cs-$^{129}$Xe and Rb-$^{129}$Xe in the temperature range $115-140\, ^{\circ}$C; both pairs are used in spin-exchange optical pumping (SEOP) to produce hyperpolarized $^{129}$Xe. $\kappa_0$ characterizes the amplification of the $^{129}$Xe magnetization contribution to the alkali-metal electronic effective field, compared to the case of a uniform continuous medium in classical magnetostatics. The measurement was carried out in "hybrid" vapor cells containing both Rb and Cs metal in a prescribed ratio, producing approximately the same vapor density for both. Alternating measurements of the optically detected EPR frequency shifts caused by the SEOP polarization and subsequent sudden destruction of the same quantity of $^{129}$Xe magnetization were made for $^{133}$Cs and either $^{87}$Rb or $^{85}$Rb. An important source of systematic error caused by power fluctuations in the pump laser that produced variable light shifts in the EPR frequency was characterized and then mitigated by allowing sufficient warm-up time for the pump laser. We measured $(\kappa_0)_{\rm CsXe}/(\kappa_0)_{\rm RbXe} = 1.215 \pm 0.007$ with no apparent temperature dependence. Based on our previous measurement $(\kappa_0)_{\rm RbXe}=518 \pm 8$, we determine $(\kappa_0)_{\rm CsXe} = 629 \pm 10$, more precise than but consistent with a previous measurement made by another research group.

This article reviews the physics and technology of producing large quantities of highly spin-polarized 3He nuclei using spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping. Both technical developments and deeper understanding of the physical processes involved have led to substantial improvements in the capabilities of both methods. For SEOP, the use of spectrally narrowed lasers and K-Rb mixtures has substantially increased the achievable polarization and polarizing rate. For MEOP nearly lossless compression allows for rapid production of polarized 3He and operation in high magnetic fields has likewise significantly increased the pressure at which this method can be performed, and revealed new phenomena. Both methods have benefitted from development of storage methods that allow for spin-relaxation times of hundreds of hours, and specialized precision methods for polarimetry. SEOP and MEOP are now widely applied for spin-polarized targets, neutron spin filters, magnetic resonance imaging, and precision measurements.

Spin-exchange optical hyperpolarization of Xe-129 gas enhances the signal-to-noise ratio in nuclear magnetic resonance experiments. The governing parameter of the Rb-Xe spin-exchange process, the so-called enhancement factor, was recently reevaluated experimentally. However, the underlying hyperfine coupling and atomic interaction potential as functions of the internuclear distance of the open-shell Rb-Xe dimer have not been accurately determined to date. We present a piecewise approximation based on first-principles calculations of these parameters contributing to the NMR and EPR frequency shifts in the low-density Rb-Xe gas mixture of relevance to hyperpolarization experiments. Both Rb electron and Xe-129 nuclear spin polarizations are estimated based on a combination of electronic-structure calculations, observed frequency shifts, and an estimate of the Rb number density. Finally, an expression for the enhancement factor in terms of modern electronic-structure theory is obtained.

We find that if solid xenon is formed from liquid xenon, denoted "ice", there is a 10% increase of $^{129}$Xe longitudinal relaxation $T_1$ time (taken at 77 K and 2 Tesla) over a trickle-freeze formation, denoted "snow". Forming xenon ice also gives unprecedented reproducibility of $^{129}$Xe $T_1$ measurements across a range of 77-150 K. This temperature dependence roughly follows the theory of spin-rotation mediated by Raman scattering of harmonic phonons (SRRS), though it results in a smaller-than-predicted spin-rotation coupling strength $c_{K0}/h$. Enriched ice $^{129}$Xe $T_1$ experiments show no isotopic dependence in bulk relaxation mechanisms at 77 K and at kilogauss fields.

The sensitivity of Rabi oscillations to low-frequency modulation (5–100 kHz) of the static longitudinal magnetic field B 0 is studied. Three regimes are considered: strong modulation (compared to the driving field strength B 1, 1–10 G), fast modulation (compared to the non-modulated Rabi frequency Ω R ), and weak-resonant modulation. The mapping of a weakly driven two-level system with modulation onto a strongly driven system without modulation suggests that different regimes of spin dynamics, previously known for a strongly driven system (i.e., multiphoton resonances), are realized under easily accessible conditions with proper choice of modulation frequency and amplitude. The experiments are straightforward to achieve in the laboratory, but can be mapped to more unconventional NMR conditions where B 1 strength is much greater than B 0.