Efficient Measurement of Free Precession Frequency in Bell-Bloom Atomic Magnetometers

The Bell-Bloom atomic magnetometer is a high-sensitivity magnetic field measuring instrument. It utilizes the free precession signal of polarized atoms to obtain the magnetic field measurement. However, the complexity of the free precession signal makes it difficult for the magnetometer to measure magnetic field information, which severely limits the application of the magnetometer. In this study, to solve this problem, a free precession frequency (FPF) measurement system is designed for the Bell-Bloom atomic magnetometer, which successfully achieves accurate, fast, and efficient frequency counting of the free precession signal. Based on the analysis results of signal characteristics, the FPF measurement system was designed and tested. The equivalent instrument sensitivity can reach 10 pT/(Hz)(1/2) in the frequency range corresponding to the magnetic field of 4060 mu T, and the system can work continuously for a long time. The system operates stably with independence within the temperature range of 275 350 K and can be further enhanced through an external temperature control system. Regarding measurement stability, the median repeatability of frequency measurement results exceeds 0.6 Hz. The FPF measurement system effectively addresses the complexities associated with the free precession signal and meets the magnetic field measurement requirements of the Bell-Bloom atomic magnetometer.