A Zero-field Atomic Gradiometer with Elliptically Polarized Laser-pumped Used for Biomagnetic Measurement

A new design of compact zero-field atomic gradiometer was proposed and integrated using alkali vapor cell and customized optical components. This gradiometer used two parallel elliptically polarized lights, whose output intensity was measured to perform gradient magnetic field detection, respectively. To improve the gradiometer's sensitivity of the magnetic field detection, the gradiometer was operated in the spin-exchange relaxation-free (SERF) regime. For the sensitivity study, the gradiometer was placed in a person-sized four-layer mu-metal magnetic shielding. With the magnetic shield closed up, the sensitivity of each channel was near 34 fT/root Hz, and the corresponding gradient sensitivity could reach 14 fT/root Hz/cm on a 1cm baseline. When the cover of magnetic shielding was removed, the magnetometer sensitivity of single channel was about 90 fT/root Hz, and the corresponding gradient sensitivity could reach 34 fT/root Hz/cm. The experimental results implied that in a poor magnetic shielding environment, the performance of magnetometer was limited due to the fluctuations of the environmental magnetic field, while the gradiometer could work well.