In situ magnetic compensation for potassium spin-exchange relaxation-free magnetometer considering probe beam pumping effect

Abstract

A novel method to compensate the residual magnetic field for an atomic magnetometer consisting of two perpendicular beams of polarizations was demonstrated in this paper. The method can realize magnetic compensation in the case where the pumping rate of the probe beam cannot be ignored. In the experiment, the probe beam is always linearly polarized, whereas, the probe beam contains a residual circular component due to the imperfection of the polarizer, which leads to the pumping effect of the probe beam. A simulation of the probe beam's optical rotation and pumping rate was demonstrated. At the optimized points, the wavelength of the probe beam was optimized to achieve the largest optical rotation. Although, there is a small circular component in the linearly polarized probe beam, the pumping rate of the probe beam was non-negligible at the optimized wavelength which if ignored would lead to inaccuracies in the magnetic field compensation. Therefore, the dynamic equation of spin evolution was solved by considering the pumping effect of the probe beam. Based on the quasi-static solution, a novel magnetic compensation method was proposed, which contains two main steps: (1) the non-pumping compensation and (2) the sequence compensation with a very specific sequence. After these two main steps, a three-axis in situ magnetic compensation was achieved. The compensation method was suitable to design closed-loop spin-exchange relaxation-free magnetometer. By a combination of the magnetic compensation and the optimization, the magnetic field sensitivity was approximately 4 fT/Hz(1/2), which was mainly dominated by the noise of the magnetic shield.

Application of spin-exchange relaxation-free magnetometry to the Cosmic Axion Spin Precession Experiment

“…where S 0 is the polarization in zero magnetic field, γ = γ e /q, q is the slowingdown factor [43], which is determined by the polarization of the potassium atoms, ∆ν is the magnetic linewidth. applied calibration magnetic field [39]. For comparison, the magnetic noise limit of the shield is also shown in the figure (single channel), which is the Johnson noise of the magnetic shield, and is approximately 7.5 fT/ √ Hz, which matches well with the theoretical prediction.…”

Optical Rotation Detection for Atomic Spin Precession Using a Superluminescent Diode

“…In order to optimize the operation of the atomic magnetometer, the residual magnetic field inside the shields with a level of 2 nT should be zeroed. All three magnetic field components are zeroed with tri-axial coils according to a cross-modulation technique to within 10 pT [29].…”

A Coil Constant Calibration Method Based on the Phase-Frequency Response of Alkali Atomic Magnetometer

“…A temperature of 473 K is obtained utilizing 99 kHz AC heating current. The residual magnetic fields are compensated after manual zeroing procedures [24]. A set of permalloy four-layer cylindrical magnetic shielding is implemented outside the coils.…”