We demonstrate a single-beam atomic magnetometer (AM) capable of measuring a three-axis magnetic field with high-sensitivity, achieved by applying a small DC offset field and a high frequency modulation field. To satisfy the miniaturization demand of AMs, an elliptically polarized light detuned by 50 GHz from the resonance transition center is employed. The circularly polarized component is used to polarize the alkali-metal atoms, while the linearly polarized light is used to detect the dynamics of the polarized spin under a magnetic field. Based on theoretical analysis, parameters that significantly affect the performance are optimized, and a sensitivity of 20 fT/Hz^1/2 in x-axis, 25 fT/Hz^1/2 in y-axis, 30 fT/Hz^1/2 in z-axis is achieved with a miniature 4 × 4 × 4 mm ⁸⁷Rb vapor cell. Moreover, we also verify that the operation principle of AMs can be used to null background magnetic fields in-situ with isotropic compensation resolution of 6.7 pT, which provides an effectively precise method for zeroing ambient magnetic field. The high-sensitivity operating of an elliptically-polarized-laser-based magnetometer provides prospective futures for constructing a compact, low-cost AM, which is particularly applicable for non-invasive bio-magnetic imaging such as array-based magnetoencephalography (MEG) and magnetocardiography (MCG).

We demonstrate the bandwidth enhancement of an all-optical spin-exchange relaxation-free (SERF) magnetometer based on amplitude-modulated (AM) light. Alkali metal atoms are modulated directly by the pump beam instead of the modulation field or radio frequency field. The first harmonic demodulation of an AM SERF magnetometer with a modulation intensity of 15 kHz results in a high bandwidth of over 11 kHz with a sensitivity of $20\hspace{0.17em}{\text{fT}/\text{Hz}}^{\mathbf{1}/\mathbf{2}}$ at 30 Hz and $60\hspace{0.17em}{\text{fT}/\text{Hz}}^{\mathbf{1}/\mathbf{2}}$ at 10 kHz. Meanwhile, the AM SERF magnetometer with DC demodulation presents the same sensitivity as a traditional DC SERF magnetometer ($6\hspace{0.17em}{\text{fT}/\text{Hz}}^{\mathbf{1}/\mathbf{2}}$ at 30 Hz). The presented technique for modulating the amplitude of the pump beam allows AM SERF magnetometers to enter the domain of high-bandwidth magnetometers and opens the door to many areas that are inaccessible to conventional magnetometers.

Alkali metal optically pumped magnetometers, with a particular emphasis on Spin-Exchange Relaxation-Free atomic magnetometers, has garnered considerable attention due to their remarkable sensitivity. In this comprehensive review, we present a succinct overview of the fundamental principle of the magnetometer and the various categories of its central sensitive unit, namely the cell. We then proceed to elaborate on the vital aspect of establishing an extremely feeble magnetic field environment that is crucial for its operation, inclusive of both active magnetic shielding and passive magnetic compensation methodologies. In furtherance, we conduct a thorough evaluation of the pros and cons of single-beam and dual-beam pump-probe scheme magnetometers, followed by a detailed investigation of their potential applications in the cardiology and brain magnetism fields. Finally, we conclude with an analysis of the hurdles and prospective development directions for alkali metal-based atomic magnetometers in the domains of magnetocardiography and magnetoencephalography, which hold the promise of substantial progress and widespread adoption in the biomedical area.

Atomic magnetometers operated in spin-exchange relaxation-free (SERF) have the potential to replace superconducting quantum interference devices (SQUIDs) in the field of biomagnetism. Here, we demonstrate the dual-axis closed-loop control of a single-beam SERF magnetometer that allows sensing of two orthogonal magnetic fields simultaneously and independently with suppressed crosstalk effect, achieved by applying a rotating modulation field and using the negative feedback. Operating in the dual-axis closed-loop mode with a miniature 4 $\times $ 4 $\times $ 4 mm ⁸⁷ Rb cell, we achieve the magnetic field sensitivity of 20 fT/Hz ^1/2 and a bandwidth of 1.8 kHz. In addition to the experimental study of the sensitivity and bandwidth, we perform a theoretical analysis of the dual-axis response and develop an effective decoupling method. The implementation of closed-loop control enables the magnetometer to be robust against the disturbance of the ambient field, which could enlarge the dynamic range, enhance the systematic stability, and suppress the crosstalk effect. Such a simple, yet high-performance SERF magnetometer could be suitable as a promising candidate in the field of biomagnetism, allowing for a denser sensor array and opening up new possibilities for noninvasive biomagnetic imaging.

We present a theoretical and experimental study of a single-beam spin-exchange relaxation-free magnetometer in ⁸⁷Rb vapor cells under different nitrogen gas pressures. The spin relaxation rate is a key component to limit the magnetic sensitivity, and the zero-field resonance method was used to measure the spin relaxation rates of different alkali metal cells. Simultaneously, in a single-beam spin-exchange-relaxation-free (SERF) magnetometer, we demonstrated that the fundamental magnetic field sensitivity was also limited by the pumping light intensity. Based on our theoretical analysis and experimental results, we determined the optimal pumping light intensity and optimal gas pressure. We experimentally demonstrated that the magnetic field sensitivity was 8.89 fT / Hz in the single-beam configuration, with an active measurement volume of 3 × 3 × 3~mm³.