Frequency response of an open loop Bell-Bloom type atomic magnetometer in an Earth-scale magnetic field

We demonstrate a portable Bell-Bloom type atomic magnetometer for measuring an earth-scale magnetic field and investigate its frequency response in both theoretically and experimentally. The frequency response of an open loop atomic magnetometer is inversely proportional to the square root of the Lorentzian function with a width of the transverse relaxation rate when the amplitude of an magnetic field noise is very small. We discuss open loop frequency responses of the magnetometer in the presense of a strong AC magnetic field or a strong white magnetic field noise.