Femtotesla ⁸⁷Rb magnetometer based on a coaxial pump-probe beam delivery system

Advancements in highly sensitive and miniaturized spin-exchange relaxation-free atomic magnetometers have attracted significant attention. Although dual-beam magnetometers with high sensitivity have been developed, miniaturization while maintaining sensitivity remains challenging. In this study, we present a novel magnetometer configuration featuring a coaxial pump-probe beam delivery system facilitated by a single polarization-maintaining optical fiber. Utilizing polarized atoms to probe the diffuse central region of a ring pump beam, we achieved optimized performance through parameter adjustments, including the power of the pump and probe beams, modulation index, and other key factors. The magnetometer exhibited a remarkable sensitivity of 15 fT/Hz^1/2. In addition, we introduced a novel method for evaluating the polarizability of alkali metals. The proposed magnetometer configuration shows considerable potential for advancing the field of highly sensitive miniaturized atomic magnetometers that are well suited for magnetocardiography (MCG) and magnetoencephalography (MEG) applications.