The integrated Vertical-Cavity Surface-Emitting Lasers (VCSELs) modules have been widely researched and manufactured accompanying with the rapid development of compact atomic magnetometers, atomic gyroscopes, atomic clocks, and the other atomic sensors. For atomic magnetometers operating in the Spin-Exchange Relaxation-Free (SERF) regime, the vapor cell should be heated to a high temperature, which may cause the built-in laser chip over-heated and module structural or optical component deformation, lowering the performance of the built-in laser module. Meanwhile, due to the space constraints, the laser module needs to achieve a large collimation beam diameter and the non-magnetic structure should be optimized to have high temperature tolerance and stable thermal dissipation. In this study, a compact non-magnetic VCSEL module is developed based on the non-magnetic structure with the abilities of optical path alignment, beam collimation, and polarization conversion. Compared with the common TO-can packaging, the proposed VCSEL module achieved low residual magnetic field generated. And the entire volume is less than 1 cm3 with the collimating beam diameter of 2 mm. The experiment evaluation result shows that the laser module could work stably in high temperature with stable thermal dissipation and sufficient thermal margin (60±10℃) for precise wavelength tuning and maintain optical performance and structural for meeting the demand of pump laser in the SERF atomic magnetometers.
A new design of compact zero-field atomic gradiometer was proposed and integrated using alkali vapor cell and customized optical components. This gradiometer used two parallel elliptically polarized lights, whose output intensity was measured to perform gradient magnetic field detection, respectively. To improve the gradiometer’s sensitivity of the magnetic field detection, the gradiometer was operated in the spin-exchange relaxation-free (SERF) regime. For the sensitivity study, the gradiometer was placed in a person-sized four-layer μ-metal magnetic shielding. With the magnetic shield closed up, the sensitivity of each channel was near 34 fT/ √ Hz, and the corresponding gradient sensitivity could reach 14 fT/√ Hz/cm on a 1cm baseline. When the cover of magnetic shielding was removed, the magnetometer sensitivity of single channel was about 90 fT/√ Hz, and the corresponding gradient sensitivity could reach 34 fT/√ Hz/cm. The experimental results implied that in a poor magnetic shielding environment, the performance of magnetometer was limited due to the fluctuations of the environmental magnetic field, while the gradiometer could work well.
Recent developments in the exploration of atomic spin instrumentation have enabled the atomic magnetometer to become the most effective detector of magnetic fields. The stability of temperature in alkali vapor cells is an important factor for ensuring the measurement accuracy of atomic magnetometers. The alkali vapor cell is usually heated to 80°C ∼ 190°C. During the heating process, although the heating system reaches a steady state, the temperature inside the alkali metal cell will still fluctuate, which will affect the accuracy of the device measurement. In this paper, K cells were simulated and analyzed by using the theory of atomic absorption spectroscopy theory. By the mathematical relationship models, the simulation analysis of the cell containing alkali vapor found that, within a small temperature fluctuation range (±1°C), the temperature fluctuation of the alkali vapor cell filled with buffer gas and the broadening parameter of the atomic absorption spectrum, as well as the frequency shift parameter all show a linear relationship. In order to facilitate the actual measurement, the relationship between the detection light intensity transmitted through the alkali metal cell and the temperature fluctuation inside the cell was also analyzed in this paper. Through simulation analysis, it is found that, within a small temperature fluctuation range (±1°C), the linear relationship between the detected light intensity transmitted through the alkali vapor cell and the temperature fluctuation inside the cell also exists.
Atomic sensing devices usually contain fiber coupling systems. A two-mirror fiber coupling system is usually used in our research to couple spatial light into polarization maintaining fiber. In order to improve the axes alignment accuracy and optical extinction ratio of this fiber coupling system for atomic sensing devices, we propose an improved method based on the influence of mirrors on beam polarization. The polarization maintaining fiber can maintain the polarization of linear polarized light only when the polarization direction coincides with the fiber. However, according to theoretical analysis by Jones Matrix and experimental results, we demonstrate that mirrors have non-negligible influence on beam polarization, which causes difficulty in axes alignment. Both dielectrical mirrors and metallic mirrors have influence on the azimuth and ellipticity of polarized light, and the influence of dielectrical mirrors is more remarkable than that of metallic mirrors. Thus we propose to add a half wave plate or a quarter wave plate in the system to compensate for the influence of mirrors, and the extinction ratio of fiber output light is consequently increased. According to the experimental results, our new approach can increase the extinction ratio by about 30dB.
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