A Room‐Temperature Operational Alignment Magnetometer Utilizing Free‐Spin Precession

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An efficient method is proposed for quantifying rubidium vapor density by analyzing the spin‐exchange rate between alkali metals. This method effectively addresses two primary challenges in measuring alkali vapor density. First, it overcomes the limitation of absorption spectroscopy to measure vapor density under optically thick conditions, typically restricted to temperature higher than 420K, equivalent to alkali vapor density exceeding . Second, it mitigates the risk of disrupting shielding functionality due to the application of a strong magnetic field, often in the range of several tens of Gauss or higher, when employing the Faraday rotation for vapor‐density measurement. The spin‐exchange rate between atoms, inherently related to the vapor density, is evident in the electron‐paramagnetic‐resonance spectrum of spin‐polarized , thereby providing a possibility for measuring alkali vapor density. To eliminate overlap between two Lorentzian curves resulting from two decomposed components of an oscillating field, a small rotating magnetic field with identical amplitude and frequency but a 90‐degree phase shift along both the x and y axes is applied. This method is successfully employed to measure vapor density in the temperature range of 373–433 K, with the measured outcomes closely matching the saturation vapor curve.

Measurement of Rubidium Vapor Density Based on Spin‐Exchange Rate

Shang,

Zou,

Zhang

et al. 2024

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Identification and Manipulation of Atomic Polarization Moments for Nonlinear Magneto‐Optical Rotation Atomic Magnetometers

Chai,

Jiang,

Liu

et al. 2024

Polarization moments play a crucial role in measuring magnetic fields for nonlinear magneto‐optical rotation (NMOR) atomic magnetometers. However, it is challenging to distinguish between each polarization moment and evaluate its effect on the magnetic resonance response signal in an alkali vapor cell with buffer gas. To address this issue, a method is proposed to identify different polarization moments through the frequency shift of the magnetic resonance response signal. The proportion of each polarization moment is determined, and it is demonstrated that the magnetic resonance response signal is affected by the hexadecapole moment, resulting in a frequency shift and a decrease in signal amplitude. To mitigate this effect, an approach is investigated to manipulate the polarization moments by flipping the phase of the pump light. Ultimately, a 15.19% increase in response amplitude is achieved in the simulated geomagnetic environment within the magnetic shield barrel. The theory and method presented here provide strong support for the study of the polarization moments in an alkali vapor cell with buffer gas, which potentially enhance the performance of NMOR atomic magnetometers.

Single‐Beam Vector Atomic Magnetometer with High Dynamic Range Based on Magnetic Field Modulation

Chen,

Jiang,

Zhao

et al. 2024

In geophysical exploration and similar applications, magnetometers need to capture the complete magnetic field information, including both the magnitude and direction. Despite recent advancements in vector atomic magnetometers, they often face issues that hinder practical use. To overcome this, a high dynamic range single‐beam vector atomic magnetometer based on the nonlinear magneto‐optical rotation (NMOR) effect is proposed, utilizing a closed‐loop system with applied three‐axis modulation magnetic fields. In this method, closed‐loop measurement is achieved using a phase‐locked loop (PLL), with the frequencies of the applied modulation magnetic fields being significantly higher than the response bandwidth of the PLL. This allows directional information to be extracted from the modulation fields response signal and magnitude information from the PLL‐locked frequency. A theoretical analysis of the proposed method is conducted by establishing an NMOR atomic magnetometer model under arbitrary magnetic field directions and deriving the method for obtaining the magnetic field direction. In further experimental validation, it is demonstrated that the vector atomic magnetometer can achieve measurement of three‐axis vector magnetic fields, with a sensitivity of approximately for magnetic field magnitude, for inclination angle, and for azimuth angle.