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The European Physical Journal D

Comment on: Magnetic field measurements in Rb vapor by splitting Hanle resonances under the presence of a perpendicular scanning magnetic field

Antoine Weis, Yongqi Shi, Z. D. Grujić

Published Mar 31, 2017• 4 citations
Publisher

Abstract

In a recent article in this journal Grewal and Pattabiraman reported on the splitting of ground state Hanle resonances (recorded with linearly polarized light) by a transverse field. They claimed a “linearly proportional” dependence on the transverse field strength and supported this observation with results from numerical simulations. In this comment we argue that the splitting occurs only beyond a certain threshold field value and that it has a strong non-linearity near threshold. We base this claim on our previously published algebraic expressions for the line shapes and support this by experimental evidence.

DOI
10.1140/epjd/e2017-70774-9

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In a recent article in this journal Grewal and Pattabiraman reported on the splitting of ground state Hanle resonances (recorded with linearly polarized light) by a transverse field. They claimed a “linearly proportional” dependence on the transverse field strength and supported this observation with results from numerical simulations. In this comment we argue that the splitting occurs only beyond a certain threshold field value and that it has a strong non-linearity near threshold. We base this claim on our previously published algebraic expressions for the line shapes and support this by experimental evidence.
We experimentally and computationally study the effect of an additional transverse magnetic field (TMF) on the Hanle resonance for a F g = 2 → F e = 3 transition of 87Rb D 2 line for magnetic field scans perpendicular to the propagation direction of the optical field. It is shown that with a π-polarized light, no resonance signal is observed in absence of the TMF. When the TMF is applied, two peaks are observed on either side of zero scanning magnetic field in the transmission spectrum. The separation between the two peaks is linearly proportional to magnitude of the TMF, which can be used for magnetometry. We applied this technique to measure magnetic field from 0.1 to 0.5 G with a pure Rb vapor cell and from 10 to 30 mG with a Rb cell containing buffer gas. These observations are attributed to the population redistribution among the ground state sublevels due to the TMF.
We present a theoretical and experimental study of the resonant circularly-polarized-light-induced Hanle effect in the ground state of Cs vapor atoms in a paraffin-coated cell. The effect manifests itself as a narrow resonance (centered at B=0B=0B=0) in the dependence of the optical transmission coefficient of the vapor on the magnitude of an external magnetic field $\stackrel{P\vec}{B}$. We develop a theoretical model that yields an algebraic expression for the shape of these resonances for arbitrary field orientations and arbitrary angular momenta of the states coupled by the exciting light, provided that the light power is kept sufficiently small. An experimental procedure for assessing the range of validity of the model is given. Experiments were carried out on the laser-driven Cs D1{D}_{1}D1​ transition both in longitudinal and transverse field geometries, and the observed line shapes of the corresponding bright and dark resonances give an excellent confirmation of the model predictions. The method is applied for determining the intrinsic longitudinal and transverse relaxation rates of the vector magnetization in the vapor and their dependence on light power.
SummaryThe ground-state level-crossing resonance, or Hanle resonance, in atomic vapors are widely used for atomic magnetometry. In this paper, we report observations of anomalous level-crossing resonances for Rb vapor in a buffer-gas cell. By optically pumping alkali atoms with a ring-shaped laser beam and detecting the spin polarization in the hole of the pumping light with an off-resonance light, we observe a polarization reversion when scanning the transverse magnetic field around zero. Both experiments and simulations are demonstrated.
We computationally compare Hanle-type resonances for a transition of the line for magnetic field scans parallel (longitudinal scan) and perpendicular (transverse scan) to the direction of propagation of the optical field in the presence of an additional transverse magnetic field (TMF). For a linearly polarized light, the coherent population trapping (CPT) resonances split at line centre and are identical for both longitudinal and transverse scans. When the probe beam ellipticity is varied, the effect of the TMF is found to be opposite for longitudinal and transverse scans. For a longitudinal scan, the splitting observed in the CPT resonance evolves into an enhanced absorption resonance with an increase in ellipticity. For a transverse scan, the splitting vanishes at higher ellipticities. This can be understood in terms of population redistribution in the ground state sublevels and near-neighbor ground state coherences created by the TMF. We also show that the enhanced absorption signal that splits the CPT resonance strongly depends on transit time, and the CPT resonance strength depends on the excited state dephasing rate.
We analyze the Hanle effect on the closed Fg equals 3 yields Fe equals 4 D2-line transition of 85Rb, by both numerical solutions of the optical Bloch equations and by experimental investigations on cell containing rubidium vapor. For laser radiation with linear polarization orthogonal to the applied magnetic field, the Hanle signal is characterized by narrow bright resonances at low laser intensities. A bright resonance Hanle signal is obtained also exciting the rubidium atoms by circularly polarized laser light and scanning a transversely applied magnetic field, at different values of an applied longitudinal magnetic field. We report experimental and numerical evidence of this new bright resonance.
Abstract We present experimental and theoretical investigations of the dependence of double Hanle resonance spectrum on the light polarization angle and the direction of the applied transverse magnetic field (TMF). The experiments are done for F g = 2 → F e = 1 transition of 87Rb D1 line using a rubidium vapor cell containing buffer gas. We show that a small light polarization component along the direction of TMF introduces asymmetry in the double Hanle resonance signal. Both the magnitude and sign of asymmetry in the signal are sensitive to the TMF orientation, suggesting a possible method for in-situ measurement of the direction of the magnetic fields generated by the coils. The physical origin of this asymmetry is explained by considering the redistribution of population among the ground-state Zeeman sublevels in the presence of TMF. In addition, we systematically vary both the polarization angle and TMF direction to study their effect on the line profile of Hanle resonances. We demonstrate that a double Hanle resonance changes to a dark Hanle resonance by rotating the light polarization vector irrespective of the TMF direction. We have developed a simple theoretical model based on a degenerate two-level system to explain our experimental observations.