Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Journal of Physics D Applied Physics

Effect of OTS coating on spin polarization and spatial homogeneity in alkali metal vapor cells for SERF magnetometers

Liu Bowen, Xiangyang Zhou, Yuhao Liu, Zhen Li, Zihao Lyu

Published Mar 26, 2026• 1 citation
Publisher

Abstract

Abstract The spin polarization and spatial homogeneity of alkali metal atoms are critical characteristics that determine the performance of spin-exchange relaxation-free magnetometers. In buffer gas cells, these characteristics are influenced by optical broadening and alkali atomic motional restriction imposed by the buffer gas. In coated cells, the protective effect of the coating on atomic spins, combined with rapid atomic diffusion, leads to significantly superior spin polarization characteristics compared to those in high-pressure buffer gas cells. However, due to neglecting the influence of atom-coating interactions on atomic motion, the existing spin polarization and spatial distribution models fail to accurately describe the polarization characteristics in coated cells. In this paper, based on the Langevin–Bloch equation, a dynamic model considering interaction effects between alkali metal atoms and the coating as well as between the pump light and the hyperfine levels of alkali metal atoms is proposed to accurately describe the spin polarization and spatial distribution in coated cells. To validate the proposed model, a series of experiments were carried out. The results demonstrate that coated cells can maintain high spin polarization and spatial homogeneity even under conditions of low pump intensity and high temperature, which are in good agreement with the simulations. This work provides a theoretical reference for the design of high-performance and low-power quantum sensors.

DOI
10.1088/1361-6463/ae57b9

Related papers

High-temperature alkali vapor cells with antirelaxation surface coatings

Scott J. Seltzer, Michael V. Romalis

Antirelaxation surface coatings allow long spin relaxation times in alkali-metal cells without buffer gas, enabling faster diffusion of the alkali atoms throughout the cell and giving larger signals due to narrower optical linewidths. Effective coatings were previously unavailable for operation at temperatures above 80 °C. We demonstrate that octadecyltrichlorosilane (OTS) can allow potassium or rubidium atoms to experience hundreds of collisions with the cell surface before depolarizing, and that an OTS coating remains effective up to about 170 °C for both potassium and rubidium. We consider the experimental concerns of operating without buffer gas and with minimal quenching gas at high vapor density, studying the stricter need for effective quenching of excited atoms and deriving the optical rotation signal shape for atoms with resolved hyperfine structure in the spin-temperature regime. As an example of a high-temperature application of antirelaxation coated alkali vapor cells, we operate a spin-exchange relaxation-free atomic magnetometer with sensitivity of 6 fT/Hz and magnetic linewidth as narrow as 2 Hz.

arXiv:0906.3054•Journal of Applied Physics•Dec 1, 2009•139 citations

Coating-Enabled Buffer-Gas-Free Vapor Cell: A New Sensor Architecture for Single-Beam SERF Magnetometers

Yi-an Xu, Yuhao Wang, Jiaxin Liu +5 more

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.

IEEE Transactions on Instrumentation and Measurement•Jan 1, 2026•0 citations

The Space Density Distribution of Alkali Metal Atoms in a SERF Atomic Magnetometer

Qiang Guo, Xuewen Li, Ning Zhang +4 more

The number density of alkali atoms in vaper cell is an important parameter for atomic magnetometer. The vapor cell is usually heated to a high temperature for the number density exceed to 1018m−3to achieve the spin-exchange-relaxation-free (SERF) process. The optical rotation of multichannel atomic magnetometers is affected by the number density distribution. We present an effective method for monitoring and analyzing the spatial distribution homogeneity of the atomic number density in the alkali metal cell within the SERF magnetometer. The numerical results from researching the model of electric heating films and ovens show that the temperature gradient increases with an increase in the cell temperature. This causes an nonuniform number density distribution based on the saturated vapor pressure curve. We present a laser absorption spectroscopy method by using the high-resolution beam profiling camera to record the power of the beam before and after the cell. An optimized optical system of the atomic magnetometer has been established by measuring the the number density variation in the spatial distribution in mm scale. The number density variation coefficient, which is introduced to evaluate the distribution homogeneity, increases from 0.0257 to 0.0333 when the temperature of the oven wall rises from 140°C to 190 °C, showing the same trend as the simulation results. The optical rotation distribution is calculated according to the magnetometer output signal formula. This study is of great interest for optimizing the oven structure and improving the stability of atomic spin polarization and sensitivity of the multichannel magnetometer.

IEEE Sensors Journal•Jan 27, 2022•13 citations

Wafer-Level Micro Alkali Vapor Cells with Anti-Relaxation Coating Compatible with MEMS Packaging for Chip-Scale Atomic Magnetometers

Yu Ji, Jintang Shang, Qi Gan +1 more

Compared with superconducting quantum interference devices, chip-scale atomic magnetometers using the wafer-level micro alkali vapor cells can be used more conveniently in the applications of geophysical mapping, health care and remote monitoring. Drastic wall collisions and decreased polarization lifetime are the main barriers for the performance of the chip-scale atomic magnetometers. In this study, OTS organic films coated on the inner surface of the micro vapor cells were used to suppress wall collisions and improve polarization lifetime of the alkali atoms in the micro cells. First of all, the fabrication process of wafer-level micro OTS coated vapor cells is introduced, the process is based on anodic bonding technology. Then the prepared wafer-level micro OTS coated vapor cells have been characterized by the water-contact angle test and measured in the micro-machined spin-exchange relaxation free(SERF) atomic magnetometers. Results show that the OTS coating is effective after anodic bonding from the water contact angle test. Results also indicate that the spin exchange relaxation free atomic magnetometer using the micro OTS-coated vapor cell can operate successfully.

IEEE Electronic Components and Technology Conference (ECTC)•May 1, 2017•4 citations

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

Siran Li, X.-G. Lu, Yinghui Zhang +3 more

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.

Photonics•Jun 1, 2026•0 citations

Improvement of spin polarization spatial uniformity in optically pumped atomic magnetometers based on counter-propagating pump beams and atomic diffusion

Junpeng Zhao, Gang Liu, Jixi Lu +9 more

Abstract In an optically pumped alkali vapor cell with a high density of atoms, the attenuation of the pump light generates a spatially non-uniform distribution of the electronic spin polarization of alkali atoms, which is detrimental to biomagnetism applications of magnetometers as well as the hyperpolarization of noble gas atoms. Therefore, in this study, we propose a new scheme to generate a nearly uniform, unsaturated spin polarization region based on counter-propagating pump beams and atomic diffusion. A finite element method-based simulation is used to demonstrate the three-dimensional distribution of the spin polarization in a spherical cell. The effects of cell temperature and pump light power on the homogeneity of the spin polarization are studied. The distribution of spin polarization near the center of the cell is experimentally measured and a 1 cm uniform spin polarization region is achieved in the center of the cell. The uniformity of spin polarization in the center region of the cell increased by 50% compared with single beam pumping. The advantage of our proposed scheme is that it can generate an unsaturated uniform region of spin polarization in the center of a cell using a single species of alkali atoms.

Measurement Science and Technology•Nov 9, 2020•49 citations
Abstract The spin polarization and spatial homogeneity of alkali metal atoms are critical characteristics that determine the performance of spin-exchange relaxation-free magnetometers. In buffer gas cells, these characteristics are influenced by optical broadening and alkali atomic motional restriction imposed by the buffer gas. In coated cells, the protective effect of the coating on atomic spins, combined with rapid atomic diffusion, leads to significantly superior spin polarization characteristics compared to those in high-pressure buffer gas cells. However, due to neglecting the influence of atom-coating interactions on atomic motion, the existing spin polarization and spatial distribution models fail to accurately describe the polarization characteristics in coated cells. In this paper, based on the Langevin–Bloch equation, a dynamic model considering interaction effects between alkali metal atoms and the coating as well as between the pump light and the hyperfine levels of alkali metal atoms is proposed to accurately describe the spin polarization and spatial distribution in coated cells. To validate the proposed model, a series of experiments were carried out. The results demonstrate that coated cells can maintain high spin polarization and spatial homogeneity even under conditions of low pump intensity and high temperature, which are in good agreement with the simulations. This work provides a theoretical reference for the design of high-performance and low-power quantum sensors.
Antirelaxation surface coatings allow long spin relaxation times in alkali-metal cells without buffer gas, enabling faster diffusion of the alkali atoms throughout the cell and giving larger signals due to narrower optical linewidths. Effective coatings were previously unavailable for operation at temperatures above 80 °C. We demonstrate that octadecyltrichlorosilane (OTS) can allow potassium or rubidium atoms to experience hundreds of collisions with the cell surface before depolarizing, and that an OTS coating remains effective up to about 170 °C for both potassium and rubidium. We consider the experimental concerns of operating without buffer gas and with minimal quenching gas at high vapor density, studying the stricter need for effective quenching of excited atoms and deriving the optical rotation signal shape for atoms with resolved hyperfine structure in the spin-temperature regime. As an example of a high-temperature application of antirelaxation coated alkali vapor cells, we operate a spin-exchange relaxation-free atomic magnetometer with sensitivity of 6 fT/Hz and magnetic linewidth as narrow as 2 Hz.
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.
The number density of alkali atoms in vaper cell is an important parameter for atomic magnetometer. The vapor cell is usually heated to a high temperature for the number density exceed to 1018m−3to achieve the spin-exchange-relaxation-free (SERF) process. The optical rotation of multichannel atomic magnetometers is affected by the number density distribution. We present an effective method for monitoring and analyzing the spatial distribution homogeneity of the atomic number density in the alkali metal cell within the SERF magnetometer. The numerical results from researching the model of electric heating films and ovens show that the temperature gradient increases with an increase in the cell temperature. This causes an nonuniform number density distribution based on the saturated vapor pressure curve. We present a laser absorption spectroscopy method by using the high-resolution beam profiling camera to record the power of the beam before and after the cell. An optimized optical system of the atomic magnetometer has been established by measuring the the number density variation in the spatial distribution in mm scale. The number density variation coefficient, which is introduced to evaluate the distribution homogeneity, increases from 0.0257 to 0.0333 when the temperature of the oven wall rises from 140°C to 190 °C, showing the same trend as the simulation results. The optical rotation distribution is calculated according to the magnetometer output signal formula. This study is of great interest for optimizing the oven structure and improving the stability of atomic spin polarization and sensitivity of the multichannel magnetometer.
Compared with superconducting quantum interference devices, chip-scale atomic magnetometers using the wafer-level micro alkali vapor cells can be used more conveniently in the applications of geophysical mapping, health care and remote monitoring. Drastic wall collisions and decreased polarization lifetime are the main barriers for the performance of the chip-scale atomic magnetometers. In this study, OTS organic films coated on the inner surface of the micro vapor cells were used to suppress wall collisions and improve polarization lifetime of the alkali atoms in the micro cells. First of all, the fabrication process of wafer-level micro OTS coated vapor cells is introduced, the process is based on anodic bonding technology. Then the prepared wafer-level micro OTS coated vapor cells have been characterized by the water-contact angle test and measured in the micro-machined spin-exchange relaxation free(SERF) atomic magnetometers. Results show that the OTS coating is effective after anodic bonding from the water contact angle test. Results also indicate that the spin exchange relaxation free atomic magnetometer using the micro OTS-coated vapor cell can operate successfully.
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.
Abstract In an optically pumped alkali vapor cell with a high density of atoms, the attenuation of the pump light generates a spatially non-uniform distribution of the electronic spin polarization of alkali atoms, which is detrimental to biomagnetism applications of magnetometers as well as the hyperpolarization of noble gas atoms. Therefore, in this study, we propose a new scheme to generate a nearly uniform, unsaturated spin polarization region based on counter-propagating pump beams and atomic diffusion. A finite element method-based simulation is used to demonstrate the three-dimensional distribution of the spin polarization in a spherical cell. The effects of cell temperature and pump light power on the homogeneity of the spin polarization are studied. The distribution of spin polarization near the center of the cell is experimentally measured and a 1 cm uniform spin polarization region is achieved in the center of the cell. The uniformity of spin polarization in the center region of the cell increased by 50% compared with single beam pumping. The advantage of our proposed scheme is that it can generate an unsaturated uniform region of spin polarization in the center of a cell using a single species of alkali atoms.