Simulation of scalar-mode optically pumped magnetometers to search optimal operating conditions

Abstract

In recent years, measuring biomagnetic fields in the Earth's field by differential measurements of scalar-mode OPMs have been actively attempted. In this study, the sensitivity of the scalar-mode OPMs under the geomagnetic environment in the laboratory was studied by numerical simulation. Although the noise level of the scalar-mode OPM in the laboratory environment was calculated to be \SI[per-mode=symbol]{104}{\pico\tesla\per\sqrt{\hertz}}, the noise levels using the first-order and the second-order differential configurations were found to be \SI[per-mode=symbol]{529}{\femto\tesla\per\centi\metre\per\sqrt{\hertz}} and \SI[per-mode=symbol]{17.2}{\femto\tesla\per\centi\metre^2\per\sqrt{\hertz}}, respectively. This result indicated that scalar-mode OPMs can measure very weak magnetic fields such as MEG without high-performance magnetic shield roomns. We also studied the operating conditions by varying repetition frequency and temperature. We found that scalar-mode OPMs have an upper limit of repetition frequency and temperature, and that the repetition frequency should be set below 4 kHz and the temperature should be set below 120 °C.