Alkali vapor cells are the core components of atomic sensing instruments such as atomic gyroscopes, atomic magnetometers, atomic clocks, etc. Emerging integrated atomic sensing devices require high-performance miniaturized alkali vapor cells, especially micro-fabricated vapor cells. In this review, bonding methods for vapor cells of this kind are summarized in detail, including anodic bonding, sacrificial micro-channel bonding, and metal thermocompression bonding. Compared with traditional through-lighting schemes, researchers have developed novel methods for micro-fabricated vapor cells under both single- and double-beam schemes. In addition, emerging packaging methods for alkali metals in micro-fabricated vapor cells can be categorized as physical or chemical approaches. Physical methods include liquid transfer and wax pack filling. Chemical methods include the reaction of barium azide with rubidium chloride, ultraviolet light decomposition (of rubidium azide), and the high-temperature electrolysis of rubidium-rich glass. Finally, the application trend of micro-fabricated alkali vapor cells in the field of micro-scale gyroscopes, micro-scale atomic clocks, and especially micro-scale biomagnetometers is reviewed. Currently, the sensing industry has become a major driving force for the miniaturization of atomic sensing devices, and in the near future, the micro-fabricated alkali vapor cell technology of atomic sensing devices may experience extensive developments.

The Rb polarization-induced magnetic field gradient affects the Xe nuclear spin relaxation properties and degrades the long-term stability of the NMR co-magnetometers. This paper proposes a combination suppressing scheme, which uses the second-order magnetic field gradient coils to compensate for the Rb polarization-induced magnetic gradient under counter-propagating pump beams. Based on the theoretical simulation, we find that the spatial distribution of the Rb polarization-induced magnetic gradient and the magnetic field distribution generated by gradient coils are complementary. The experimental results indicate that the compensation effect is 10% higher under the counter-propagating pump beams scheme compared with the compensation effect under the conventional single beam. Besides, due to a more uniform spatial distribution of electronic spin polarization, the Xe nuclear spin polarizability is improved and the signal-to-noise ratio (SNR) of NMR co-magnetometers could be further enhanced. The study provides an ingenious method for suppressing magnetic gradient in the optically polarized Rb-Xe ensemble, which is expected to improve the performance of the atomic spin co-magnetometers.

The accuracy of atomic sensor is determined by the transverse nuclear spin relaxation time (T₂). As the longitudinal nuclear spin relaxation time (T₁) is the upper limit of T₂, it becomes an important metric for evaluating the merits of alkali vapor cells. However, the conventional method for measuring T₁ of pulse delay takes dozens of minutes, which will increase the effect of random errors during the testing process. In order to solve this problem, a method to quickly estimate the value of T₁ is proposed by suppressing the influence of spin exchange relaxation and magnetic field gradient relaxation terms on T₂. Experimental results indicate that the accuracy is maintained at above 95%, and the testing time is reduced to less than 5%.

This paper propose a novel and easy-to-implement method that employs a predefined circular configuration for biplanar coils to produce a transverse uniform magnetic field. The coil windings are distributed on the plane within a preset radius range, fulfilling the design criteria of preserving a central light-passing hole, an ideal feature for miniature atomic sensors. Compared to the conventional saddle coil design method, this method can minimize the aspect ratio to unity while maintaining high magnetic field uniformity. Moreover, to further improve the magnetic field uniformity in the target region, the particle swarm optimization (PSO) algorithm is introduced to optimize the regularization coefficient of the coils. Compared with the classic saddle coil structure, the simulation results demonstrate that the proposed method not only reduces the aspect ratio from 2 to 1, but also improves the maximum inhomogeneity relative error from 9.74 × 10⁻³ to 5.33 × 10⁻³ in the target region. To verify the accuracy of the results, the quintuple magnification coil scheme was manufactured by printed circuit board (PCB) technology avoiding the error caused by manual winding. Finally, the experimental results confirm that the magnetic field uniformity is nearly consistent with the theoretical analysis results.

The uniform magnetic field coils within the magnetic shielding layer find numerous applications, particularly in miniature NMRG sensors. However, the target magnetic field generated by the designed coils is inevitably distorted due to the adjacent ferromagnetic material that attracts the magnetic field. To address this issue, a novel image method based on uniqueness principle is proposed, which takes into account the coupling effect between the magnetic shielding box (MSB) and the coils. The particle swarm optimization (PSO) algorithm is employed to assist the novel image method in designing highly uniform axial magnetic field coils within a compact MSB. The validity and uniformity of the designed coils are verified by the finite element method (FEM), demonstrating the maximum relative uniformity error of magnetic flux density B_z is 2.6×10⁻⁴ compared to the original point. Moreover, two classic configurations of uniform magnetic field coils, the Helmholtz coils and the 9449 coils, are introduced to compare the uniformity with the designed coils. Finally, the designed scheme was measured both within and without MSB and the experimental results indicated that the relative uniformity error of B_z was in good agreement with the reference values. These findings further substantiate the applicability of the proposed method to miniature atomic sensors that require generating a highly uniform magnetic field within the MSB.