Triaxial vector measurement of nonlinear magneto-optical rotation atomic magnetometer based on dual-frequency orthogonal magnetic modulation

In applications such as biomagnetic measurement, biochemical sample analysis, and fundamental physics research, high-sensitivity triaxial vector measurement in the near-zero-field is essential for extracting richer source information. To address the demand for high sensitivity and a wider measurable field range in near-zero-field applications, we propose a single-beam vector nonlinear magneto-optical rotation (NMOR) magnetometer based on dual-frequency orthogonal magnetic modulation. With orthogonal modulation fields applied along the y- and z-axes, the magnetic-field components along these two axes are mapped in a cross-axis manner onto distinct frequency components of the optical-rotation signal, whereas the x-axis magnetic-field component is directly obtained from the DC component. A theoretical model is developed to describe the nonlinear dependence of the signal on the modulation parameters and to guide system optimization. Under the optimized conditions, the magnetometer achieves a triaxial measurement range exceeding ±120nT while retaining high-speed response, with measured bandwidths of 915 Hz, 1040 Hz, and 3577 Hz for the x-, y-, and z-axes, respectively. Meanwhile, the dual-frequency orthogonal magnetic modulation reduces the influence of low-frequency technical drifts of the modulated channels. As a result, sensitivities of 49fT/Hz, 50fT/Hz, and 75fT/Hz are achieved for the x-, y-, and z-axes, respectively. These results demonstrate the potential of the proposed scheme for practical near-zero-field vector magnetic-field sensing requiring both high sensitivity and fast response over an extended measurement range.