We analyze nonlinear magneto-optical rotation (NMOR) in rubidium vapor subjected to continuously-scanned magnetic field. By varying magnetic-field sweep rate, a transition from traditionally-observed dispersive-like NMOR signals (low sweep rate) to oscillating signals (higher sweep rates) is demonstrated. The transient oscillatory behavior is studied versus light and magneticfield parameters, revealing a strong dependence of the signals on magnetic-sweep rate and light intensity. The experimental results are supported with density-matrix calculations, which enable quantitative analysis of the effect. Fitting of the signals simulated versus different parameters with a theoretically-motivated curve reveals presence of oscillatory and static components in the signals. The components depend differently on the system parameters, which suggests their distinct nature. The investigations provide insight into dynamics of ground-state coherence generation and enable application of NMOR in detection of transient spin couplings.

Abstract. We experimentally and computationally study the effect of an additional transverse magnetic field (TMF) on the Hanle resonance for a Fg = 2 → Fe = 3 transition of 87 Rb D2 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.

The influence of the closed transition on the neighboring and open transitions of the 87Rb D2 line, partially resolved under Doppler broadening, is studied at different ellipticities in the Hanle configuration with longitudinal and transverse magnetic field scans. We show that a sign reversal from an electromagnetically induced transparency (EIT) resonance to an electromagnetically induced absorption (EIA) resonance occurs with an increase in ellipticity for the transition in a transverse field scan. This transformation is not observed for a longitudinal field scan. These observations are attributed to the higher amplitude of the EIA resonance for the transition in transverse field scans for elliptical polarized light. The EIA character in the Hanle transmission profile of and transitions is enhanced (weakened) when the laser beam frequency is detuned towards (away from) the transition. We show by computation that at higher ellipticities, a transformation from an EIT to an EIA resonance for the transition occurs at low frequency shifts (towards the transition) in a transverse field scan.

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.

Nonlinear magneto-optical rotation is studied under non-equilibrium conditions. The polarization rotation of linearly polarized light traversing a rubidium vapor cell is observed versus the timedependent (swept) longitudinal magnetic field in the presence of static transverse magnetic fields. Presence of the transverse fields modifies the character of the observed signals. In particular, for weaker transverse fields, field sweep leads two-harmonic oscillation of the polarization rotation while crossing zero. Unlike the steady-state, it was found that two-frequency oscillations observed in the transient signals, are independent of the transverse-field direction. For stronger transverse fields, the oscillations deteriorate eventually reaching a situation when no-oscillating dynamic signal, with distinct minimum close to zero field, is observed. Experimental results are supported with theoretical analysis based on the density-matrix formalism. The analysis confirms all the features of experimental results while providing an provide intuitive explanation of the observed behavior based on angular-momentum probability surfaces used for density-matrix visualization.