Modulation crosstalk effect analysis on single-beam SERF atomic magnetic gradiometer

Gradiometers can achieve higher sensitivity, which benefits from their excellent ability to suppress the common mode noise. However, the capability of the dual-modulation gradiometer will be affected by the crosstalk between two pairs of magnetic modulation coils. In this paper, we first establish the crosstalk model for the dual-modulation gradiometer, which reveals both magnetic field variations and magnetic field gradients introduced by the crosstalk in the gradiometer system. Based on the crosstalk coefficient in the proposed model, we can calibrate the modulating magnetic field to maximize the performance of the gradiometer. The experiments indicate that the measured crosstalk coefficients are consistent well with the theory model, and the crosstalk-model-based calibration method can optimize the gradiometer performance. As a result, the calibrated sensitivity of the dual-modulation gradiometer is $\text{15 fT/}\sqrt{\text{Hz}}$, which is better than the uncalibrated sensitivity of $\text{22 fT/}\sqrt{\text{Hz}}$ and is a little worse than the single-modulation gradiometer of $\text{10 fT/}\sqrt{\text{Hz}}$. By suppressing the effects of crosstalk, this dual-modulation design of the gradiometer configuration can be used to construct a miniaturized weak magnetic sensor, which is expected to be used for the measurement of fetal magnetocardiography (fMCG).