Dead-zone-free single-beam atomic magnetometer based on free-induction-decay of Rb atoms

TL;DR

This paper presents a dead-zone-free atomic magnetometer using a single laser beam with a novel pumping scheme, achieving consistent sensitivity in all magnetic field directions, which enhances practical applications.

Contribution

The authors introduce a simple experimental scheme that eliminates dead zones in FID atomic magnetometers by using combined polarization components and amplitude modulation for synchronous atomic pumping.

Findings

No zero-amplitude signals for any magnetic field direction.

Sensitivity range of 3.2 - 8.4 pT/√Hz in all directions.

Potential for miniaturized, practical magnetic sensing applications.

Abstract

Free-induction-decay (FID) magnetometers have evolved as simple magnetic sensors for sensitive detection of unknown magnetic fields. However, these magnetometers suffer from a fundamental problem known as a "dead zone," making them insensitive to certain magnetic field directions. Here, we demonstrate a simple experimental scheme for the dead-zone-free operation of a FID atomic magnetometer. Using a single laser beam containing equal strength of linear- and circular-polarization components and amplitude-modulation at a low-duty cycle, we have synchronously pumped the rubidium-87 atoms with both first- and second-order frequency harmonics. Such a pumping scheme has enabled us to observe the free Larmor precession of atomic spins at a frequency of $\Omega_L$ (orientation) and/or 2$\Omega_L$ (alignment) in a single FID signal, depending on the direction of the external magnetic field. We observed that the amplitude of the FID signal does not go to zero for any magnetic field direction, proving the absence of dead zones in the magnetometer. The magnetometer has a sensitivity in the range of 3.2 - 8.4 pT/$\sqrt{Hz}$ in all directions. Our experimental scheme can be crucial in developing miniaturized atomic magnetometers for various practical applications, including geomagnetic applications.