Triaxial Alignment Magnetometer Utilizing Free-Spin Precession in the Geomagnetic Range

In this paper, we present a triaxial alignment magnetometer based on free-spin precession deployed in the geomagnetic range. Existing vector measurement methods often require complex optical setups, heating structures, and laser modulation. This study addresses this challenge by employing a linearly polarized probe beam to induce atomic alignment and subsequently detecting the optical polarization rotation caused by the pulsed radio frequency field. The experiment is conducted in a paraffin-coated cell without buffer gas at room temperature, containing rubidium with natural abundance. We report triaxial measurements with a static magnetic field amplitude of approximately 50 $\mu{\text{T}}$ (close to Earth's magnetic field), where the noise levels for each axis are approximately 5.3 ${\text{pT/}}\sqrt{{\text{Hz}}}$, 4.7 ${\text{pT/}}\sqrt{{\text{Hz}}}$, and 9.3 ${\text{pT/}}\sqrt{{\text{Hz}}}$ respectively. The proposed method demonstrates a simple structure suitable for cost-effective and versatile applications.