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Optics Express

In-situ measurement of vapor cell temperature based on obliquely incident pump light for NMR sensors

Chuanming Yin, Xiangyang Zhou, Weiqian Wang, Zhen Li, Bowen Liu, Zihao Lyu, JinGuo Mu, Zehao Wang, Xiaoxuan Xie

Published Jun 4, 2026• 0 citations
Publisher

Abstract

This paper presents a pump-light-based in-situ temperature measurement method for nuclear magnetic resonance (NMR) vapor cells under oblique optical incidence. To miniaturize the NMR sensor, a thin vapor cell is employed, in which both the orthogonal pump and probe light are introduced obliquely through one surface of the vapor cell. A model is developed to relate pump-light absorption to Rb atomic density, thereby enabling inference of the vapor cell temperature. The model includes polarization distortion, polarization-dependent window transmission attenuation, effective optical path length, and the coupling between optical absorption and atomic polarization. Experimental results show that the proposed method achieves the lowest RMSE of 0.179 K and reduces it by at least 68.2% compared with several commonly used fitting methods, enabling accurate in-situ temperature measurement in miniaturized NMR sensors under obliquely incident pumping.

DOI
10.1364/oe.604431

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This paper presents a pump-light-based in-situ temperature measurement method for nuclear magnetic resonance (NMR) vapor cells under oblique optical incidence. To miniaturize the NMR sensor, a thin vapor cell is employed, in which both the orthogonal pump and probe light are introduced obliquely through one surface of the vapor cell. A model is developed to relate pump-light absorption to Rb atomic density, thereby enabling inference of the vapor cell temperature. The model includes polarization distortion, polarization-dependent window transmission attenuation, effective optical path length, and the coupling between optical absorption and atomic polarization. Experimental results show that the proposed method achieves the lowest RMSE of 0.179 K and reduces it by at least 68.2% compared with several commonly used fitting methods, enabling accurate in-situ temperature measurement in miniaturized NMR sensors under obliquely incident pumping.
The atomic density of an alkali vapor cell is a critical factor in determining the performance of atomic magnetometers. This paper presents a novel method to detect the density of an alkali atomic ensemble under arbitrary polarization states. By establishing a comprehensive model that correlates the absorption spectrum with the incident light’s polarization, our approach enables real-time and flexible measurements across varying temperatures and polarization angles. Experimental validations are conducted by systematically rotating a quarter-wave plate and controlling the vapor cell temperature, thereby collecting transmission spectra at multiple polarizations. The results demonstrate that the proposed method simplifies density measurements while preserving high accuracy, laying a solid foundation for further research on Spin-Exchange Relaxation-Free (SERF) atomic magnetometers. This technique serves as a versatile and effective tool for in-situ monitoring of alkali metal vapor density in various sensor applications.
Abstract For optically pumped atomic magnetometers, the attenuation of the pumping light through the alkali-metal vapor due to light absorption is related to the number density of alkali-metal atoms. In this study, we propose an in-situ measurement and control method of atomic number density based on light absorption in the temperature range of 60 °C–160 °C, which is a much wider temperature range than considered in previous reports. A light absorption-density model is proposed to accurately describe the relationship between the light transmittance and the atomic number density. The influence of static and oscillating magnetic fields on the atomic number density measurement is also analyzed. Based on this model, a close-loop system is constructed to control the atomic number density using an electric heater. The experimental results exhibit that the proposed method can limit the fluctuation of the atomic number density in the range of 1.4%.
The spin transverse relaxation time ( T 2 ) of atoms is an important indicator for magnetic field precision measurement. Especially in optically-pumped atomic magnetometer, the linewidth of the magnetic resonance signal is one of the most important parameters of sensitivity, which is inversely correlated with T 2 of atoms. In this paper, we propose four methods, namely spin noise spectroscopy signal fitting, radio-frequency free induction decay (RF-FID) signal fitting, ω m (modulation frequency)-broadening fitting, and magnetic resonance broadening fitting, for in-situ measurement T 2 of atomic vapor cells based on light-atom interactions. Meanwhile, T 2 of three Rubidium (Rb) atomic vapor cells with different parameters are measured and discussed by using these four methods. A comparative analysis visualizes the characteristics of the different methods and the effects of buffer gas on T 2 of Rb atoms. Through theoretical and experimental analysis, we assess the applicability of each method and concluded that the RF-FID signal fitting method provides the most accurate measurements due to the timing sequence control system, which results in a cleaner measurement environment. Furthermore, we demonstrate and qualitatively analyze the relationship between temperature and T 2 of Rb atoms. This work may offer valuable insights into the selection of atomic vapor cells and it is also applicable for the spin-exchange relaxation-free region.
Miniature (<few cm3) vapor-cell based devices using optical pumping of alkali atoms, such as atomic clocks and magnetometers, today mostly employ vertical-cavity surface-emitting lasers as pump light sources. Here, we report on the demonstration of optical pumping in a microfabricated alkali vapor resonance cell using (1) a microfabricated Rb discharge lamp light source, as well as (2) a conventional glass-blown Rb discharge lamp. The microfabricated Rb lamp cell is a dielectric barrier discharge (DBD) light source, having the same inner cell volume of around 40 mm3 as that of the resonance cell, both filled with suitable buffer gases. A miniature (∼2 cm3 volume) test setup based on the Mz magnetometer interrogation technique was used for observation of optical-radiofrequency double-resonance signals, proving the suitability of the microfabricated discharge lamp to introduce efficient optical pumping. The pumping ability of this light source was found to be comparable to or even better than that of a conventional glass-blown lamp. The reported results indicate that the micro-fabricated DBD discharge lamp has a high potential for the development of a new class of miniature atomic clocks, magnetometers, and quantum sensors.
Ne comagnetometer-cells at different temperatures, pump light powers, and mole fractions of K. The method was further verified by the conventional laser-absorption-spectroscopy method. The new approach has the advantage to measure the density ratio of the optically-thick hybrid alkali atoms, while requiring no additional magnetic field necessary for conventional magnetic-field induced Faraday-rotation techniques. It also has the advantage of in-situ measuring the density ratio under exactly the normal operation of the devices, which means that the errors caused by the heating-effect of the strong pump light and the temperature drift during long-term operation can be real-time monitored.
Abstract Zero-field level-crossing resonances (LCRs) underlay one of the most robust and simplest techniques in atomic magnetometry. LCR-based miniaturized magnetic field sensors have already found relevant applications in biology and medicine. Such sensors utilize a single circularly polarized light wave to interact with alkali-metal atoms (usually Rb or Cs) and to observe the LCR in a vapor-cell transmission when a transverse magnetic field is scanned around zero value. A high-temperature regime (T ≈ 120 − 160°C) is required to achieve a desirable sensitivity of measurements. It can be a problem for some applications, especially in a multi-channel mode of operation. Here, we consider two spectroscopy techniques that can provide high-contrast and narrow LCRs under a relatively low temperature of the cell (≤60°C). These techniques imply using two light waves: the pump wave to polarize the atoms and the probe one to register the resonance. A cubic glass cell of 5×5×5 mm3 size is used in the experiments. It is filled with cesium vapors and neon as a buffer gas. The results can be used for developing a miniaturized low-power high-sensitivity magnetic field sensor for biomedical applications.