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Chinese Physics B

In-situ measurement of cell temperature by spin-relaxation rate analysis for an atomic magnetometer

Bingquan Zhao, Zhe Qi, Jianlong Wang, Li-Hua Wu, Qian-Yun 倩云 Zhao 赵, J. J. Wei, Weiren Liu, Ling-Xin 令鑫 Kong 孔

Published Sep 17, 2025• 0 citations
Publisher

Abstract

Abstract Alkali-metal vapor cells are the core sensing components of atomic magnetometers. To achieve high-sensitivity magnetic field measurements, the cells require heating and stabilization at high temperatures. Here, we propose an in-situ temperature measurement method for a vapor cell of an atomic magnetometer based on spin-relaxation analysis. This technique establishes a direct functional correlation between the cell temperature and the spin-relaxation rate under low pumping power conditions. Experimental validation within the temperature range of 90 °C–130 °C confirms the accuracy of this approach. We further investigate the effects of magnetic fields on measurement precision and demonstrate the long-term, high-precision capabilities of temperature detection. This non-invasive technique presents a critical advantage for precise thermal optimization of atomic magnetometers.

DOI
10.1088/1674-1056/ae07bf

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Electrical heating elements, which are widely used to heat the vapor cell of ultrasensitive atomic magnetometers, inevitably produce a magnetic field interference. In this paper, we propose a novel measurement method of the amplitude of electrical-heating-induced magnetic field for an atomic magnetometer. In contrast to conventional methods, this method can be implemented in the atomic magnetometer itself without the need for extra magnetometers. It can distinguish between different sources of magnetic fields sensed by the atomic magnetometer, and measure the three-axis components of the magnetic field generated by the electrical heater and the temperature sensor. The experimental results demonstrate that the measurement uncertainty of the heater’s magnetic field is less than 0.2 nT along the x-axis, 1.0 nT along the y-axis, and 0.4 nT along the z-axis. The measurement uncertainty of the temperature sensor’s magnetic field is less than 0.02 nT along all three axes. This method has the advantage of measuring the in-situ magnetic field, so it is especially suitable for miniaturized and chip-scale atomic magnetometers, where the cell is extremely small and in close proximity to the heater and the temperature sensor.
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This study proposes an in situ method for measuring the equilibrium spin polarization and its longitudinal spatial distribution in a spin-exchange relaxation-free (SERF) atomic magnetometer. The total relaxation rate was determined by analyzing the steady-state response of the magnetometer to the triaxial magnetic field. The transfer coefficient between spin polarization along the probe beam axis and the steady-state response was derived from the optical depth of the probe light and the incident/transmitted power through the vapor cell. By applying a DC magnetic field along the sensitive axis and combining the total relaxation rate with the transfer coefficient, the equilibrium spin polarization value under zero-field conditions was obtained. The equilibrium spin polarization distribution along the pump beam propagation direction was measured, showing consistent trends with simulation results, with a maximum relative error of less than 5%. The expanded uncertainty of the proposed equilibrium spin polarization measurement method ranges from 0.8% to 9.7%. The advantages of this method include no requirement for additional optical field or magnetic field modulation, immunity to temperature and temperature gradients, and the capability to directly determine the equilibrium spin polarization value.