Miniaturized atomic sensors of magnetic field and inertia have great potential to be applied as geophysical instruments and in the detection of biomolecules. The distribution of the electronic spin polarization plays a key role as it defines the amount of noble gas that can achieve a state of hyperpolarization, which in turn determines the technique's accuracy and, consequently, its resolution. However, the current techniques for electronic spin polarization imaging are unsuited for the operating conditions of miniaturized atomic sensors besides only accomplishing submillimeter spatial resolution. In this study, optical magnetic resonance is applied to obtain electronic spin polarization images with a spatial resolution of 60  μm experimentally and 10  μm theoretically. This corresponds to an increase by one order of magnitude in resolution when compared to previous reports of electronic spin polarization imaging. By sweeping the RF frequency of the magnetic field while applying a magnetic field gradient of 0.22 [Formula: see text], it is possible to measure electronic spin polarization images for different average photon spins and pump beam positions. Spin polarization images present a high degree of correlation with pump beam images. Furthermore, this image method can be applied to suppressing the inhomogeneities in miniaturized cells, leading to a gain in signal-to-noise ratio. It also offers an opportunity to experimentally perform two-dimensional atomic polarization manipulation in the gas phase, optically transparent solids, and liquids.

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.

A stable inner working environment is essential for NMR sensors, which requires the absence of remnant magnetic fields and fluctuations caused by the surrounding magnetic fields. In this study, we utilized analytical formulations to derive transverse and longitudinal magnetic shielding factors for multilayer cylindrical magnetic shielding. Subsequently, we proposed a novel method for designing and improving the shielding factor by optimizing the spacing of every pair of adjacent layers within a limited volume. The final design result of the multilayer cylindrical magnetic shielding features optimally designed varying layer spacing, which are associated with a specific length and diameter. After optimization, the transverse shielding factor increased by 5.53%, 8.99%, and 13.51% for the three-, four-, and five-layer shields, respectively, compared to traditional magnetic shielding. The opening in the axial center of the magnetic shielding barrel may cause leakage of the magnetic flux and inhomogeneous remnant magnetic induction. We introduced a stovepipe to the end cap of the axial shield based on the finite element method, resulting in an improvement in the homogeneity of remnant magnetic induction. This modification widened the axial uniform region of the innermost shielding layer by approximately 9 cm within 52.5 cm in our simulation. To implement our proposed optimization method, we established and manufactured a four-layer cylindrical magnetic shielding with stovepipes and varying layer spacing. Moreover, the results indicate that this optimal method works for other applications in which multilayer magnetic shielding is required.

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