In-Situ Detection for Atomic Density in the K-Rb-21Ne Co-Magnetometer via an Optical Heterodyne Interferometry

Abstract

The low-frequency fluctuations of the atomic density within the cell can induce the longterm drift of the K-Rb-21Ne spin-exchange relaxation-free (SERF) co-magnetometer output, such that the accurate measurement of in situ atomic density is of great significance for improving the performance of co-magnetometer. In this paper, the complex refractive index model of the spin ensembles under the hybrid optical pumping condition is established first, according to which the relation between atomic density and its complex refractive index is revealed and an optical heterodyne-based scheme for atomic density detection is proposed. The dependence of the atomic density on the demodulated phase signal from the optical heterodyne-based scheme is provided by numerical simulations. After that, a dual acousto-optics frequency shifter (AOFS)-based optical heterodyne interferometry is constructed with a noise level below 1 mrad/Hz for frequencies > 1 Hz, and a compact SERF co-magnetometer is implemented as the testing medium, by which the atomic density detection with resolution of 0.40 K @ 473 K is reached and the experimental results agree well with theoretical simulations. Moreover, the detection scheme proposed in this paper has the properties of high detection sensitivity and immunity to laser power fluctuation, which are also proved experimentally.

Enhancing Dynamic Performance in K-Rb-21Ne Co-Magnetometers through Atomic Density Optimization

“…Ultra-sensitive co-magnetometers use alkali metal and noble gas spin species to simultaneously and accurately measure rotation [1], and have been used in a variety of applications, including rotation sensing [2][3][4], biomagnetism [5], and fundamental physics such as testing for CPT symmetry [6,7], the Electron Dipole Moment [8], and spin-depended forces [9,10]. In recent years, atomic spin co-magnetometers based on Spin-Exchange Relaxation-Free (SERF) principles have become a significant development direction in inertial instrumentation [11][12][13].…”

High-precision alkali-atom density measurement and control methods using light absorption for dual-beam SERF magnetometers

“…However, the measurement of the spinexchange relaxation rate was time-consuming, which made this method unsuitable for alkali-metal density control. Besides, Liu et al also achieved the detection of atomic density in a K-Rb- 21 Ne co-magnetometer using optical heterodyne interferometry which requires a complex optical path structure [17] . In summary, although the above methods have been successfully utilized to accurately measure alkali-atom density, these measurement methods are time-consuming or involve complex additional optical paths.…”