Performance Enhancement by Investigating on Excitation Parameters of Helium Cell in ⁴He Optically Pumped Magnetometer

In 4He optically pumped magnetometers (OPMs), the helium cell is an essential component, mainly affected by excitation parameters that influence the perfor- mance of the magnetometer. This study aims at analytically and experimentally exploring suitable parameters based on frequency values and power densities of excitation to achieve optimal performances. First, a plasma model is established and theoretically analyzed in this field. Then, a favorable frequency value of the high-frequency (HF) signal is calculated based on the impedance of the He cell measured at a certain HF frequency, and an experiment on sensitivity varying with power density absorbed by the cell is conducted. Experimental results indicate that the optimal value is 45 MHz, the desirable power density is 1.1 W/cm2 within the scope of 0.6–1.8 W/cm2, and the sensitivity is improved prominently, thereby providing systematic sensitivity of 29.4 pT/Hz $^{1/2}$ in the frequency from 1 to 30 Hz. Theoretical analyzes and experimental results demonstrate a prominent performance improvement of the magnetometer by optimizing the parameters of the excitation circuit. The proposed method reliably provides a potential direction for future research on the sensitivity enhancement of He cells.