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arXiv:2312.06078 · Optics Express

Comparison and analysis of methods for measuring the spin transverse relaxation time of rubidium atomic vapor

Lulu Zhang, Yongbiao Yang, Junye Zhao, Yanhua Wang, Junmin Wang

Published Nov 17, 2024• 0 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1364/oe.542760

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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.
The transverse relaxation time (T2) is an important indicator to determine the fundamental sensitivity limit of alkali-metal atomic magnetometers. We propose a method based on the principle of longitudinal field modulation that obtains T2 by scanning the transverse static magnetic field. The previous technique of extracting T2 from the linewidth of the modulation frequency and the traditional magnetic-resonance-broadening-fitting method are also described. The T2 measurements of Cesium (Cs) atoms are carried out through these three methods, whose operating environments are applicable to different atomic magnetometers, respectively. The method that we propose can be used for obtaining the T2 of Cs atoms as well as detecting the transverse static magnetic field and is customized for the study of the Cs–Xenon ensemble for the construction of nuclear magnetic resonance gyroscopes. Moreover, the relationship between the limit sensitivities and cell temperatures is further studied in the experiment.
A free-induction-decay (FID) type optically-pumped rubidium atomic magnetometer driven by a radio-frequency (RF) magnetic field is presented in this paper. Influences of parameters, such as the temperature of rubidium vapor cell, the power of pump beam, and the strength of RF magnetic field and static magnetic field on the amplitude and the full width at half maximum (FWHM) of the FID signal, have been investigated in the time domain and frequency domain. At the same time, the sensitivities of the magnetometer for the single-pass and the triple-pass probe beam cases have been compared by changing the optical path of the interaction between probe beam and atomic ensemble. Compared with the sensitivity of ∼21.2 pT/Hz1/2 in the case of the single-pass probe beam, the amplitude of FID signal in the case of the triple-pass probe beam has been significantly enhanced, and the sensitivity has been improved to ∼13.4 pT/Hz1/2. The research in this paper provids a reference for the subsequent study of influence of different buffer gas pressure on the FWHM and also a foundation for further improving the sensitivity of FID rubidium atomic magnetometer by employing a polarization-squeezed light as probe beam, to achieve a sensitivity beyond the photo-shot-noise level.
We analyze the transverse nuclear magnetizations of 129Xe and 131Xe in a vapor cell containing natural Xe, 87Rb, and buffer gases. The Xe atoms are polarized through spin-exchange optical pumping (SEOP) with Rb atoms under low-magnetic-field conditions. From the free-induction-decay (FID) signal, we measure the nuclear magnetization of the Xe atoms in the Xe-Rb vapor cell. Furthermore, we measure the dependence of the gyromagnetic ratio on the magnetization of 129Xe and 131Xe by examining the amplitude of the FID signal of each isotope, and we evaluate the relationship between the magnetic field gradient and transverse relaxation rate for both of the 129Xe and 131Xe isotopes.
Traditional practice of suppressing low-frequency noise in atomic magnetometers is mainly through the application of magnetic field modulation, while magnetic fields of this kind introduce extra transverse relaxation, which results in a decrease of sensitivity. In this study, a novel method of measuring relaxation rate induced by spin-destruction, wall collisions and modulation magnetic fields is proposed. The optical pumping model is studied both in optical-thin and optical-thick vapor cell through the analysis of total relaxation, thus the optical pumping rate can be separated from total relaxation by analyzing the optical depth. Furthermore, based on the analysis of optical pumping rate and relaxation rate, the polarization of the electron ensemble was evaluated. A compact magnetometer with single-beam configuration is developed for the proof of concept, and the experimental results show good agreements with theoretical calculation. Our method provides a simple and feasible approach to in-situ measurement of transverse relaxation rate and optical pumping rate with physical structure of the device untouched, which is especially advantageous for designing and optimizing compact atomic magnetometers.
Abstract Atomic precision measurement technologies based on the Spin‐Exchange Relaxation‐Free (SERF) regime play a vital role in advanced research and the relaxation characteristics of the vapor cell are key factors that determine the sensitivity and stability of measurements. As a result, the accurate measurement of relaxation time has become an important research focus. In this work, a novel and efficient method is proposed for measuring relaxation time based on the technique of Electromagnetically Induced Transparency (EIT), and validate it experimentally under both geomagnetic and magnetically shielded conditions. By utilizing the D1 transition line of 87 Rb atoms, a three‐level ‐type EIT system is constructed. An optical setup is developed, incorporating a specially designed light source, vapor cell, temperature‐controlled heating structure, and magnetic shielding. After turning off the coupling beam, the relaxation characteristics are obtained by measuring the transmission spectrum of the probe beam. Under geomagnetic conditions, the fitted fast and slow relaxation times are 0.56 and 105.67 ms, respectively; under magnetic shielding, the corresponding values are 47.88 and 100.32 ms. Furthermore, the influence of temperature and coupling beam power on the relaxation process is investigated, providing theoretical insight for improving the performance of atomic precision measurement technologies.
We propose and demonstrate a radio-frequency (rf) atomic magnetometer based on parametric resonances. Previously, most rf atomic magnetometers are based on magnetic resonances and their sensitivities are often limited by spin-exchange relaxation. Here, we introduce a novel scheme for an rf magnetometer where the rf magnetic field is measured by exciting the parametric resonances instead of magnetic resonances using parametric modulation fields. In this way, the spin-exchange relaxation is almost eliminated. Benefiting from the low spin relaxation rate, the parametric resonance scheme exhibits a narrower linewidth and stronger signal, which results in a higher sensitivity. With a 6×6×3 mm^{3} Rb atomic vapor cell, we developed an rf atomic magnetometer with a noise floor of 2 fT/Hz^{1/2}, which is about one order of magnitude higher than the sensitivity achieved in the magnetic-resonance-based scheme. The presented rf detection scheme holds promise in advancing rf atomic magnetometers and brings new insight into their various applications.