arXiv subjects

Raghwinder Singh Grewal

Publications and source records attributed to Raghwinder Singh Grewal.

4 recordsLinked to original sources

arXiv2025

Dead-zone-free single-beam atomic magnetometer based on free-induction-decay of Rb atoms

Free-induction-decay (FID) magnetometers have evolved as simple magnetic sensors for sensitive detection of unknown magnetic fields. However, these magnetometers suffer from a fundamental problem known as a "dead zone," making them insensitive to certain magnetic field directions. Here, we demonstrate a simple experimental scheme for the dead-zone-free operation of a FID atomic magnetometer. Using a single laser beam containing equal strength of linear- and circular-polarization components and amplitude-modulation at a low-duty cycle, we have synchronously pumped the rubidium-87 atoms with both first- and second-order frequency harmonics. Such a pumping scheme has enabled us to observe the free Larmor precession of atomic spins at a frequency of $Ω_L$ (orientation) and/or 2$Ω_L$ (alignment) in a single FID signal, depending on the direction of the external magnetic field. We observed that the amplitude of the FID signal does not go to zero for any magnetic field direction, proving the absence of dead zones in the magnetometer. The magnetometer has a sensitivity in the range of 3.2 - 8.4 pT/$\sqrt{Hz}$ in all directions. Our experimental scheme can be crucial in developing miniaturized atomic magnetometers for various practical applications, including geomagnetic applications.

physics.atom-ph↗

arXiv2020

Magnetometry using sodium fluorescence with synchronous modulation of two-photon resonant light fields

We report a new technique for generating magnetic resonance with synchronous modulation of two-photon resonant light fields. Magnetic resonances in fluorescence from a sodium cell are measured to demonstrate suitability of this technique for remote magnetometry. A strong magnetic resonance with its dip corresponding to the Larmor frequency is produced in the presence of a transverse magnetic field. An additional resonance at 3\{Omega_L} is observed, which can be used to determine the magnetic field orientation. We have developed a theoretical model based on the density matrix equations to verify our experimental observations. An average magnetic field sensitivity of 41 \mathbf{pT}/\sqrt{\mathbf{Hz}} is measured using light duty cycles ranging from 35% to 10%. We have discussed possible changes that can be made to improve the sensitivity of this scheme further.

physics.atom-ph↗

arXiv2020

Light ellipticity and polarization angle dependence of magnetic resonances in rubidium vapor using amplitude-modulated light: Theoretical and experimental investigations

We report on experimental and theoretical investigations of the polarization dependence of magnetic resonance generated by synchronous optical pumping. Magnetic resonances with narrow linewidth are generated experimentally using a rubidium vapor cell with octade-cyltrichlorosilane (OTS) antirelaxation coating on inner walls. We studied the effect of light ellipticity on the amplitudes and widths of magnetic resonances by matching the light modulation frequency with 2 Ω_L (alignment) and Ω_L(orientation) in a Bell-Bloom interaction geometry, where Ω_L corresponds to the Larmor frequency. Both 2 Ω_L and \OmegaL resonance amplitudes showed a strong dependence on the light ellipticity. In addition, we showed that the duty cycle of light modulation changes the slope of amplitude variations in 2Ω_L and Ω_L resonances with light ellipticity. As a potential application, we showed that the difference between 2Ω_Land Ω_Lresonance amplitudes can be used for in situ measurement of light ellipticity. We also studied the dependence of 2Ω_L and Ω_L resonance amplitudes on the polarization angle of linearly polarized light. These amplitudes oscillate periodically with the polarization angle. We found this oscillatory behavior to be sensitive to the tilt in magnetic field direction from the polarization plane. Such a property could be used to realize a vector magnetometer. A density matrix based theoretical model is developed to simulate the magnetic resonance spectrum for different light polarizations. Our theoretical model accurately reproduces the above mentioned experimental observations.

physics.atom-ph↗

arXiv2019

Transient dynamics of nonlinear magneto-optical rotation in the presence of transverse magnetic field

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 time-dependent (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.

physics.atom-ph↗