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arXiv:2004.09064 · Journal of Physics B Atomic Molecular and Optical Physics

Modulation induced splitting of the magnetic resonance

Rita Behera, Swarupananda Pradhan

Published Aug 10, 2020• 5 citations
arXivHTMLPDF

Abstract

Abstract The splitting of magnetic resonance induced by a frequency modulated linearly polarized light field is presented for Hanle experimental configuration. The experiment is carried out with thermal Rubidium atoms in an anti-relaxation coated glass cell. The observed splitting corresponds to steady-state behaviour of the system over an integrated time scale that is longer than the modulation frequency. The splitting is only observed for dark resonances, with left and right circularly polarized light simultaneously coupled to the atomic system. The split components are separated by half of the modulation frequency with the central component lying at zero-magnetic field. The absence of odd split components at single photon resonance is consistent with the theoretical calculation. The different components of the split profile have distinct response to the direction of the transverse magnetic field. The response is captured by the theoretical calculation and the underlying physical mechanism is discussed. These studies will be useful in metrology and advancement of vector atomic magnetometer.

DOI
10.1088/1361-6455/abade2

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Optics Express•Jun 17, 2013•35 citations
Abstract The splitting of magnetic resonance induced by a frequency modulated linearly polarized light field is presented for Hanle experimental configuration. The experiment is carried out with thermal Rubidium atoms in an anti-relaxation coated glass cell. The observed splitting corresponds to steady-state behaviour of the system over an integrated time scale that is longer than the modulation frequency. The splitting is only observed for dark resonances, with left and right circularly polarized light simultaneously coupled to the atomic system. The split components are separated by half of the modulation frequency with the central component lying at zero-magnetic field. The absence of odd split components at single photon resonance is consistent with the theoretical calculation. The different components of the split profile have distinct response to the direction of the transverse magnetic field. The response is captured by the theoretical calculation and the underlying physical mechanism is discussed. These studies will be useful in metrology and advancement of vector atomic magnetometer.
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.
In recent years diode laser sources have become widespread and reliable tools in magneto-optical spectroscopy. In particular, laser-driven atomic magnetometers have found a wide range of practical applications. More recently, so-called magnetically silent variants of atomic magnetometers have been developed. While in conventional magnetometers the magnetic resonance transitions between atomic sublevels are phase-coherently driven by a weak oscillating magnetic field, silent magnetometers use schemes in which either the frequency or the amplitude of the light beam is modulated. Here we present a theoretical model that yields algebraic expressions for the parameters of the multiple resonances that occur when either amplitude-, frequency-, or polarization-modulated light of circular polarization is used to drive the magnetic resonance transition in a transverse magnetic field. The relative magnitudes of the resonances that are observed in the transmitted light intensity at harmonic mmm of the Larmor frequency ${\ensuremath{\omega}}_{L}$ (either by DC or phase sensitive detection at harmonics qqq of the modulation frequency ${\ensuremath{\omega}}_{\mathrm{mod}}$) of the transmitted light are expressed in terms of the Fourier coefficients of the modulation function. Our approach is based on an atomic multipole moment representation that is valid for spin-oriented atomic states with arbitrary angular momentum FFF in the low light power limit. We find excellent quantitative agreement with an experimental case study using (square-wave) amplitude-modulated light.
As is well known a linearly polarized resonant laser will cause atoms to generate a magnetic tensor moment (MTM) by polarizing them. When there exists an external magnetic field, it is possible that the moment will precess around the field. In the presence of a radio frequency (RF) exciting source, we investigate theoretically the dependence of time-independent (direct current, DC), the first and second harmonic signal of the MTM precession on magnetic vector field, and obtain its analytical solution by solving the Liouville equation. The results show that the interference of both harmonic components will result in the precession spectrum evidently varying. A detailed explanation is described in the following. For the DC signal, Rabi frequency Ω of 1/(2√2) is a spectral splitting threshold. When it is greater than the threshold, the interference will cause single resonant absorption dip characterized usually to split into two dips, which has not been reported before to the best of our knowledge, and the separation between both the dips may be expressed as √3√Ω2+Ω4 -Ω2-1. For the first harmonic signal including symmetric and antisymmetric component, an interference fringe will appear near the center of antisymmetric part when Ω >1/(2√2), simultaneously its symmetric part behaves like the above dc component, such as splitting threshold and separation between both dips. With regard to the second harmonic signal, it is found that the interference can also lead to the width of the second harmonic decreasing to 38% compared with the case of the first harmonic signal. At the optimum RF Rabi frequency, on the assumption that noise spectral density is constant, it is theoretically shown that the most sensitive magnetometer, realized by the DC component or the first or second harmonic signal of the precession, depends only on the angle between the light polarization and the measured magnetic field.In fact, we are able to obtain the modules of the measured magnetic vector by RF resonant frequency. The angle between the magnetic field and the laser polarization is determined just by the ratio of the intensity of the DC component to the intensity of the second harmonic signal and the ratio between the intensities of the symmetric parts of two harmonic signals in resonance, and another orientation angle between the measured field projection at the plane perpendicular to the light polarization and the direction of RF source depends on the phase difference between the antisymmetric components of both harmonic signals. Consequently, we demonstrate a vectorial atomic magnetometer that is realized by using the RF source and the linearly polarized resonant laser without rotating laser polarization. This kind of atomic magnetometer with simple sensor structure is easy to integrate vector magnetometer array which will be suitable for solving the inverse problem and geomagnetic navigation.
Abstract It is common for senior physics students at many universities to perform optical pumping experiments using a rubidium cell in an integrated apparatus. Such experiments provide an encounter with atomic structure in the context of a standard technique of modern atomic physics. Typically, students investigate radiofrequency resonances between Zeeman levels and measure hyperfine splitting. Despite its pivotal role in aligning the apparatus the so-called zero-field resonance is usually not investigated in such experiments. However it is instructive to look more closely at this phenomenon. We show that it is a consequence of a residual transverse magnetic field that is the result of the inability to align precisely the optical axis of the apparatus in the local N – S direction. The measured width and depth of the resonance-like minimum in transmission is found to be consistent with a very small relaxation rate for the rubidium atoms. In an appendix we show further that the measurements compare well with theory for the Hanle effect in the ground state for an arbitrary magnetic field direction relative to the optical axis of the experiment.
The method of transferring the frequency of an optically detected magnetic resonance both up and down by an arbitrary value is implemented in a single-beam optical pumping scheme by modulating the linearly polarized beam component. The possibility of observing the Hanle resonance in a magnetic field virtually zeroed upon transition to a rotating coordinate system is demonstrated. A model experiment was carried out, confirming the fundamental feasibility and effectiveness of the method. Keywords: Optically detectable magnetic resonance, optical resonance frequency transfer, Hanle effect, Bell-Bloom scheme, quantum magnetometer.
We report on a study of polarization-modulation experiments on the 4 → 3 hyperfine component of the D1 transition in Cs vapor contained in a paraffin-coated cell. The laser beam's polarization was switched between left- and right-circular polarization at a rate of 200 Hz. Variations of the transmitted light power were recorded while varying the amplitude of a transverse magnetic field. The power shows electromagnetically induced transparency (EIT) resonances when the atomic Larmor frequency matches a harmonic of the modulation frequency. We made a quantitative study of the resonance amplitudes with square-wave modulations of various duty cycles, and find an excellent agreement with recent algebraic model predictions.