Robust off-resonance frequency stabilization and low-noise suppression for serf co-magnetometer probe laser

The spin-exchange relaxation-free (SERF) atomic co-magnetometer is highly sensitive to low-frequency noise and requires exceptional laser frequency stability. However, a significant challenge is stabilizing the probe laser frequency far from the atomic resonance line. We propose a transfer cavity-based off-resonance laser frequency stabilization system that enhances robustness while ensuring both long-term frequency stability and effective low-frequency noise suppression for the probe laser at frequencies far-detuned from the atomic resonance. In theory, we analyze potential sources of low-frequency noise and establish transfer function model for the frequency stabilization control loops. Based on the model, static and dynamic analyses are conducted to develop optimization strategies for low frequency noise reduction and enhanced system robustness. Experimental results show that at a frequency far from the atomic resonance line, the low-frequency noise of the probe laser is significantly reduced by two orders of magnitude compared to the free-running laser, achieving a frequency noise level of 126.4 Hz/Hz^1/2 at 100 Hz, and frequency standard deviation of 54.68 kHz over 12 h. This work significantly improves frequency stability and robustness of far-detuned probe laser in SERF atomic co-magnetometer, while achieving cost-effectiveness and effective low-frequency noise suppression.