Three-Axis Atomic Magnetometer Employing Longitudinal Field Modulation

A three-axis atomic magnetometer employing longitudinal field modulation is demonstrated theoretically and experimentally. The operational condition of this magnetometer is that the longitudinal z-component of the external magnetic field is dominant, which is achieved by applying a bias magnetic field. The longitudinal z-component of the external magnetic field is extracted from the modulation frequency, which tracks the resonance frequency, and the transverse
x
- and
y
- components are, respectively, obtained from the quadrature and the in-phase signals of a lock-in amplifier. Through feedback control, the magnitude and direction of an external magnetic field can be measured in real time, and an excellent orthogonality of the three-axis magnetometer response is obtained. By optimizing the parameters of this three-axis magnetometer, a longitudinal field sensitivity of 0.3
${\rm{pT}/ \rm{Hz}}^{1/ 2}$
and a transverse field sensitivity of 2
${\rm{pT}/ \rm{Hz}}^{1/ 2}$
are achieved.