Measurement of noise of current source by pump-probe atomic magnetometer

Abstract

<sec>The stable and reproducible magnetic field generated by a precision current source and a coil is usually used to calibrate the sensitivity of an atomic magnetometer. The noise of the current source directly determines the noise of the magnetic field. Therefore a highly sensitive atomic magnetometer can be used to measure the noise of the current source.</sec><sec>In this paper, a pump-probe atomic magnetometer is used to measure and estimate the noises of two current sources in a wide range. Firstly, in order to suppress the drift of magnetic field, which is caused by the drift of the current source or the gradual change of the magnetization of magnetic shielding materials, a method of implementing the magnetic compensation by using a precision source B2912A with small current is proposed and realized. The experimental results show that the magnetic compensation significantly suppresses the drift of magnetic field and reduces the amplitude of the power spectral density of magnetic field values to less than 0.1 Hz, but have little effect on the amplitude of the power spectral density of magnetic field values more than 0.1 Hz. Secondly, the relationship between the sensitivity of the pump-probe atomic magnetometer and the noises of two current sources in a wide range is respectively verified experimentally. When the magnetic field varies from 100 nT to 10000 nT, the sensitivity of the pump-probe atomic magnetometer increases stepwise from 0.2 pT/Hz<sup>1/2</sup> to 15 pT/Hz<sup>1/2</sup> by using a precision source B2912A to generate the magnetic field, while the magnetometer sensitivity is always about 20 pT/Hz<sup>1/2</sup> by using a DC power analyzer N6705B to generate the magnetic field. When the magnetic field increases from 5000 nT to 6000 nT, the current resolution of B2912A changes from 100 nA to 1 μA, leading the peak to peak of the measured magnetic field to change from 23 pT to 230 pT. In the same transformation process of the magnetic field, the current resolution of N6705B is always about 2 μA, causing the peak to peak of the measured magnetic field to maintain at 300 pT. The experimental results show that the sensitivity of the pump-probe atomic magnetometer is limited by the noise of the magnetic field, thus the current noise can be estimated by the sensitivity of the pump-probe atomic magnetometer. When the magnetic field is set to 5000 nT, the current of B2912A or N6705B supplied to the coil is 94.8 mA, while the noise of B2912A or N6705B is 22.70 nA/Hz<sup>1/2</sup> or 0.39 μA/Hz<sup>1/2</sup>, respectively. The value of the current noise is about 20% of the value of the current resolution, which will be given a more reasonable explanation by combining the data processing process and the calibration details of current source in the future.</sec><sec>Our research is of great significance in calibrating the sensitivity of magnetic sensor, developing the high-precision current sources, and co-developing the magnetic induction metrology and current metrology.</sec>