Compact high-bandwidth single-beam optically-pumped magnetometer for biomagnetic measurement

Optically-pumped magnetometer (OPM) has been of increasing interest for biomagnetic measurements due to its low cost and portability compared with superconducting quantum interference devices (SQUID). Miniaturized spin-exchange-relaxation-free (SERF) OPMs typically have limited bandwidth (less than a few hundred Hertz), making it difficult to measure high-frequency biomagnetic signals such as the magnetocardiography (MCG) signal of the mouse. Existing experiments mainly use SQUID systems to measure the signal. In this paper, we introduce a prototype miniaturized single-beam SERF magnetometer with a bandwidth of ∼ 1 kHz. Instead of operating the OPM in a closed-loop mode to improve the bandwidth of the OPM, which usually has a poorer performance in high-frequency range, we use the power-broadening effects to shorten the spin relaxation time and thus a faster response to the magnetic fields to be measured. Combined with light power stabilizations to improve both the sensitivity and stability, our magnetometer has a low noise floor of 30 fT / Hz^1/2, which has been successfully adopted to measure the MCG signal of the mouse.