  Miniaturized atomic magnetometers, particularly spin-exchange relaxation-free
atomic magnetometers, have been emerging in clinical imaging applications such
magnetocardiography and magnetoencephalography. Miniaturization, portability,
and low cost are primary development targets for bio-magnetic imaging
technologies, as well as high sensitivity and spatial and time resolution. In
this paper, we propose a low-cost solution for a bio-magnetic imaging system
based on atomic magnetometers, in which one laser source is used for a
multi-channel atomic magnetometer sensor array. A novel design is demonstrated
for a miniaturized spin-exchange relaxation-free atomic magnetometer,
consisting of a single-beam double-pass configuration based on an optical fiber
circulator. The effects of temperature and laser power on the zero-field
magnetic resonance line-width are characterized, and the experimental results
show that the present design achieves better performance, than a traditional
single-beam single-pass configuration. The noise power spectrum shows that the
closed-loop miniaturized atomic magnetometer reaches a sensitivity of
approximately 120 fT/Hz$^{1/2}$ at a bandwidth of 10 Hz. This design is
especially suitable for atomic magnetometers operating in arrays as a basic
building element for low-cost bio-magnetic imaging systems.

Atomic Physics