Single-Beam Double-Pass Miniaturized Atomic Magnetometer for Biomagnetic Imaging Systems

Miniaturized atomic magnetometers (AMs), particularly spin-exchange relaxation-free (SERF) AMs, have been emerging in clinical imaging applications such as magnetocardiography (MCG) and magnetoencephalography (MEG). Miniaturization, portability, and low cost are primary development targets for biomagnetic imaging technologies, as well as high sensitivity, temporal, and spatial resolution. In this article, we propose a low-cost solution for a biomagnetic imaging system based on AMs, in which one laser source is used for a multichannel AM sensor array. A novel design is demonstrated for a miniaturized SERF AM, 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 linewidth are characterized, and the experimental results show that the present design achieves better performance, compared with a traditional single-beam single-pass configuration. The magnetic field noise spectrum shows that such single-beam double-pass miniaturized AMs reach a sensitivity of approximately 86 fT/Hz ^{1/2} at a frequency of 10 Hz when operating in the single-channel mode and a sensitivity of approximately 40 fT/Hz ^{1/2} when operating in magnetic differential mode with two sensors sharing one laser source and a 6-mm baseline. A typical adult MCG signal with all the visible P, QRS-complex, and T waves is recorded by the magnetometer in the single-channel mode. This design is especially suitable for AMs operating in arrays as a basic building element for low-cost biomagnetic imaging systems.