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We measured the spatial homogeneity of spin polarization, which is directly related to the sensitivity and magnetic linewidth of an optically pumped atomic magnetometer with a hybrid cell of K and Rb atoms. This was done by changing the position of the probe beam. Furthermore, for comparison, we also measured the sensitivity and magnetic linewidth of atomic magnetometers with single K and single Rb cells, and found that optically thick atoms were spin polarized homogeneously with the hybrid cell. Optically thin alkali metal vapor can be spin polarized homogeneously, and the spin polarization transfers to an optically thick alkali metal vapor. An atomic magnetometer with the hybrid cell was found to be more effective in realizing simultaneous signal measurements at different locations with the uniform sensitivity and magnetic linewidth. [ABSTRACT FROM AUTHOR]

We have developed a K-Rb hybrid optically pumped atomic magnetometer (OPAM) for biomagnetic measurements. With this hybrid OPAM, we used a linear photodiode array and a charge-coupled device (CCD) sensor to instantaneously measure 1-D and 2-D magnetic field distributions generated by a test coil, respectively. The measured distributions were compared with those calculated using the Biot–Savart law and showed good agreement for the linear photodiode array; however, in the case of the CCD sensor in the area away from the test coil, the intensity of the detected magnetic field was slightly different from the calculated one, possibly because of the diffusion of the spin-polarized atoms as well as smear and blooming in the CCD sensor. The sensitivity of the OPAM was 5–6 pT/Hz ^1/2 using the linear photodiode array and $\sim 10$ pT/Hz ^1/2 using the CCD sensor. In future experiments, we plan to fabricate a sensor cell with a high density of probe atoms and reduce the noise generated in the electronic circuitry of the detectors in order to increase sensitivity. [ABSTRACT FROM AUTHOR]