An Atomic Gradiometer with Two Parallel Elliptically Polarized Laser-pumped Used for Magnetocardiography*

A new type of compact atomic gradiometer was designed and integrated. The gradiometer utilizes two parallel elliptically polarized light beams to optically pump atoms. To achieve higher sensitivity, the gradiometer works in the SERF regime. The circularly polarized components of both elliptical laser beams are used to polarize atoms, while the linearly polarized components are used to detect the atoms' spin polarization state. These two parallel beams of the gradiometer do not interfere with each other and can work independently in the magnetometer mode or constitute a gradiometer. The sensitivity of the magnetometer is near 22 fT/$\sqrt{\mathrm{Hz}} $, and the corresponding gradient sensitivity can reach 14 fT/cm/$ \sqrt{\mathrm{Hz}} $ on a 1 cm baseline. Using this gradiometer, magnetocardiography measurement was successfully performed. The experimental results show that in a poor magnetic shielding environment, the magnetometer cannot clearly measure the magnetocardiography signals due to the fluctuations of the environmental magnetic field, while the gradiometer can successfully extract clear magnetocardiography signals. The common-mode rejection ratio, bandwidth and working range of the magnetic gradiometer were also measured and explained.