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Photonics

Buffer Gas Pressure Optimization for Atomic Spin Relaxation Suppression in Ultra-High-Sensitivity SERF Magnetometers

Siran Li, X.-G. Lu, Yinghui Zhang, Yafang Zou, Yanning Ma, Li Cao

Published Jun 1, 2026• 0 citations

Abstract

Optically pumped magnetometers (OPM) are core quantum payloads for geomagnetic remote sensing. Among them, the spin-exchange relaxation-free (SERF) OPM with aT-level ultimate sensitivity stands as mainstream. While enlarging the alkali-metal vapor cell of the SERF OPM enhances sensitivity, it triggers complex atomic spin relaxation, notably intensified magnetic field gradient relaxation. To address the dilemma of atomic spin relaxation regulation and the engineering requirements of ultra-high-sensitivity SERF magnetometers, this paper constructs an analytical model of the total relaxation rate that comprehensively considers wall-collision relaxation, spin-destruction collision relaxation, and longitudinal/transverse magnetic field gradient relaxation, etc. The analytical relationship between buffer gas pressure and total relaxation rate for a commonly used spherical vapor cell is derived, revealing the intrinsic correlation among cell size, atomic spin relaxation, and optimal pressure. Based on the theoretical model, the filling parameters of the vapor cell are optimized, and experimental measurements are carried out. The theoretical relaxation results are highly consistent with the experimental ones, realizing the precise optimization of buffer gas pressure. The optimization method proposed in this paper provides a theoretical basis and parameter guidance for the engineering preparation of alkali-metal vapor cells for high-sensitivity SERF magnetometers in remote sensing applications.

DOI: 10.3390/photonics13060546

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Alkali metal vapor cells are fundamental components in quantum sensors, and their relaxation characteristics critically influence both sensitivity and system stability. In Spin-Exchange Relaxation-Free (SERF) atomic magnetometers, although spin-exchange collisions are effectively suppressed, wall-collision-induced relaxation remains the primary limiting factor. A coating-enabled buffer-gas-free vapor cell (CBF-VC) is proposed as a novel sensor unit, realized through multilayer octadecyltrichlorosilane (OTS) selfassembled molecular coatings. The CBF-VC is integrated into a single-beam SERF atomic magnetometer, and experimental validation is conducted. The results indicate a significant extension of the wall collision relaxation time from 40.19 ms. This extended relaxation time directly enhances the magnetometer sensitivity by 48%, confirming the feasibility of CBF-VCs as a measurement-oriented vapor cell architecture. The findings demonstrate not only the effectiveness of anti-relaxation coatings, but also a new instrumentation pathway for advancing next-generation quantum sensing.

Nowadays, quantum sensor research is a very interesting and popular topic. High-sensitivity magnetic field measurements using quantum sensors have evolved into the most sensitive magnetic field sensor category today with the invention of atomic magnetometers operating in the spin-exchange relaxation-free (SERF) regime. This letter was prepared to investigate the magnetic field sensitivity changes depending on the buffer gas, temperature, and laser intensity using indigenously produced atomic vapor cells. In addition, the aim was to determine the optimum operating conditions of the atomic magnetometer operating in the SERF regime. As a result, the resonance linewidth and signal-to-noise ratio were measured, and the minimum detectable magnetic field was calculated. According to the obtained results, the lowest magnetic field for Cells I–III was measured as 5.12, 4.21, and 4.81 pT, respectively. The lowest magnetic field of all conditions was obtained in vapor cell (Cell-II) at 100 °C with 5 mW laser intensity. As a result, it has been experimentally proven that under the same conditions, increasing the buffer gas pressure in vapor cells can narrow the resonance linewidth, and the magnetic field sensitivity can be improved by increasing the laser intensity applied to the vapor cells.