Ingenious Method for Measuring the Non-Orthogonal Angle of the Saddle-Shaped Coils of an SERF Atomic Magnetometer System

The spin exchange relaxation free (SERF) atomic magnetometer has been a research hotspot due to its ultra-high sensitivity. The SERF atomic magnetometer's sensitivity is subject to the accuracy of its compensating magnetic field and the calibration signal. These two processes need a tri-axial coil system to generate the required magnetic fields, which are directly affected by the non-orthogonality of the tri-axial coil system, especially the non-orthogonality between the x-and y-axes coils. In order to solve this problem, an ingenious and effective method for measuring the non-orthogonal angle between the x-and y-axes in a magnetic coil system has been demonstrated in this paper for the first time. This measurement method was only based on the dynamics of the SERF atomic magnetometer and did not need any additional calibration equipment. A large dc magnetic field B_y was applied to the y-axis, such that the magnetic field B_yx projected from B_y on to the x-axis could be measured. By then solving the relevant trigonometric function, we could obtain the non-orthogonal angle. Using this method, we experimentally obtained the non-orthogonal angle of about 84.08° between the x-and y-axes saddle-shaped coils, with a variance of about 0.14°. Finally, the correctness of this method for calculating the non-orthogonal angle was analyzed.