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Recently, optically pumped atomic magnetometers (OPAMs) replacing superconductive quantum interference device-based magnetometers have attracted a considerable amount of attention. To apply the OPAMs to biomagnetic field measurements, simultaneous multilocation measurements are required. To fulfill the specific requirement, we have developed a hybrid cell, which contains potassium and rubidium atoms. The OPAM with a hybrid cell can enhance the spatial homogeneity due to the suppression of pump-beam absorption. Thus, we can have multiple measurement locations inside a hybrid cell with multiple pump and probe lasers. In this paper, we proposed a novel method to accomplish simultaneous multilocation measurements based on pump-beam modulation. Using two optical choppers, we operated a two-channel OPAM with two modulated pump beams. We investigated the signal strength of the OPAM as a function of modulation frequency and found that the signal strength decreased as the modulation frequency increased. Subsequently, we measured the magnetic field distributions generated from a loop coil to validate the proposed method and could confirm that they showed good agreements with the theoretical values. These results demonstrate the feasibility of the proposed method based on pump-beam modulation. [ABSTRACT FROM AUTHOR]

Superconducting quantum interference devices are widely used in basic and clinical biomagnetic measurements such as low-field magnetic resonance imaging and magnetoencephalography primarily because they exhibit high sensitivity at low frequencies and have a wide bandwidth. The main disadvantage of these devices is that they require cryogenic coolants, which are rather expensive and not easily available. Meanwhile, with the advances in laser technology in the past few years, optically pumped atomic magnetometers (OPAMs) have been shown to be a good alternative as they can have adequate noise levels and are several millimeters in size, which makes them significantly easier to use. In this study, we used an OPAM module operating at a Larmor frequency of 5 kHz to acquire NMR and MRI signals. This study presents these initial results as well as our initial attempts at imaging using this OPAM module. In addition, we have designed a liquid-cooled pre-polarizing coil that reduces the measurement time significantly. [ABSTRACT FROM AUTHOR]

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]

An optically pumped atomic magnetometer using a hybrid cell of potassium and rubidium atoms was demonstrated to yield high sensitivity to magnetic fields. We operated the magnetometer with the four possible combinations of optically pumped and optically probed atoms and found that the combination of optically pumped potassium and optically probed rubidium showed the highest sensitivity among the four combinations because the rubidium atoms were denser than those of potassium. Furthermore, we investigated the dependence of the sensitivity on the power densities of the pump and probe beams and the wavelength of the probe beam. The magnetometer using the hybrid cell required higher pump-beam power and had narrower magnetic linewidth than those of the single alkali-metal cell. However, the magnetic linewidth was larger than the theoretical value, ignoring the spin relaxation caused by the spin-exchange collisions. By adjusting the laser conditions, the highest sensitivity approached 30 fTrms/\rm Hz^1/2. [ABSTRACT FROM AUTHOR]