In-situ measurement and close-loop control of atomic number density in an optically pumped magnetometer based on light absorption

For optically pumped atomic magnetometers, the attenuation of the pumping light through the alkali-metal vapor due to light absorption is related to the number density of alkali-metal atoms. In this study, we propose an in-situ measurement and control method of atomic number density based on light absorption in the temperature range of 60 °C–160 °C, which is a much wider temperature range than considered in previous reports. A light absorption-density model is proposed to accurately describe the relationship between the light transmittance and the atomic number density. The influence of static and oscillating magnetic fields on the atomic number density measurement is also analyzed. Based on this model, a close-loop system is constructed to control the atomic number density using an electric heater. The experimental results exhibit that the proposed method can limit the fluctuation of the atomic number density in the range of 1.4%.