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.
Nuclear magnetic resonance (NMR) oscillator is an optical atomic sensor which is developed to measure inertial angular velocity with navigation grade accuracy. It utilizes semiconductor laser, miniaturized magnetic shield and atom vapor cell to realize nuclear magnetic resonance, optical pump and detection in a very small volume (about 10cc to 100cc). NMR oscillator is much more compact than other classic gyros such as fiber optic gyro (FOG), so it is a potential substitution of FOG in the next generation compact navigation grade IMU. To achieve this goal, it is essential to analyse the short-term noise and long-term drift performance of the NMR oscillator. It is also necessary to decompose and track the random error source for further improvements of the device. We propose using the Allan Variance (AVAR) method to both analyse the drift performance and characterize the short-term noise. We also built an NMR oscillator prototype to test and verify the method’s accuracy. Theory analysis and experimental results are compared with the classic FOG for deeper comprehension of the differences between these two inertial sensors. We hope this is helpful for those who design the IMU system.
Atomics magnetometers achieve remarkable accuracy, applying to production and scientific research. However, their size and bulk components make it difficult to achieve higher accuracy. We investigate the influence of the skew angle of the pump beam on the optical pumping rate in an atomic magnetometer. An analysis based on the Bloch equation is proposed to decrease evaluate optical errors in the process of production and assembly. When the incident angle is non-zero, the pumping rate has a projection in the direction of a static magnetic field. By establishing the pumping rate equation, the pumping rate of each position in the vapor cell in the direction of static magnetic field at different pump light skew angles is calculated in our study. The sensitivity was measured experimentally to demonstrate the simulation results. The results indicate that the optical pumping rate decreases as the amplitude of skew angle and propagation distance increasing which can be evaluated by one-dimensional distribution while the decay rate increases with the rise of the angle. The simulation values of the rubidium pumping rate, obtained with an incident angle of 0.5° , in the center of the vapor cell are reduced by 46%. The sensitivity decreases with the increasing skew angle similar to the attenuation trend of the optical pumping rate but not the same. Our work provides a reference for evaluating the optical error of atomic magnetometer which is useful for miniaturization design.
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