Ultra-sensitive multi-channel optically pumped atomic magnetometers based on the spin-exchange relaxation-free (SERF) effect are powerful tools for applications in the field of magnetic imaging. To simultaneously achieve ultra-high spatial resolution and ultra-high magnetic field sensitivity, we proposed a high-resolution multi-channel SERF atomic magnetometer for two-dimensional magnetic field measurements based on a digital micro-mirror device (DMD) as the spatial light modulator for a single vapor cell. Under the optimal experimental conditions obtained via spatial and temporal modulation of the probe light, we first demonstrated that the average sensitivity of the proposed 25-channel magnetometer was approximately 25fT/Hz 1/2 with a spatial resolution of 216µm. Then, we measured the magnetic field distribution generated by a gradient coil and compared the experimentally obtained distributions with those calculated via finite element simulation. The obtained g value of 99.2% indicated good agreement between our experimental results and the theoretical calculations, thereby confirming that our proposed multi-channel SERF magnetometer was effective at measuring magnetic field distributions with an ultra-high spatial resolution.
Ultra-sensitive multi-channel optically pumped atomic magnetometers based on the spin-exchange relaxation-free (SERF) effect are powerful tools for applications in the field of magnetic imaging. To simultaneously achieve ultra-high spatial resolution and ultra-high magnetic field sensitivity, we proposed a high-resolution multi-channel SERF atomic magnetometer for two-dimensional magnetic field measurements based on a digital micro-mirror device (DMD) as the spatial light modulator for a single vapor cell. Under the optimal experimental conditions obtained via spatial and temporal modulation of the probe light, we first demonstrated that the average sensitivity of the proposed 25-channel magnetometer was approximately 25fT/Hz 1/2 with a spatial resolution of 216µm. Then, we measured the magnetic field distribution generated by a gradient coil and compared the experimentally obtained distributions with those calculated via finite element simulation. The obtained g value of 99.2% indicated good agreement between our experimental results and the theoretical calculations, thereby confirming that our proposed multi-channel SERF magnetometer was effective at measuring magnetic field distributions with an ultra-high spatial resolution.
The spin-exchange relaxation-free (SERF) atomic magnetometer has high sensitivity for magnetic field measurement, and is of great significance in frontier physics research, biomagnetic detection and other fields. In recent years, as one of the important development directions, its high spatial resolution and multi-channel magnetic field detection capabilities have been further extended. In this paper, based on the three-axis in-situ magnetic field zeroing method (MFZM), the accurate measurement of three-axis static magnetic field is realized, and the using of the digital micro-mirror device (DMD) further supports the measurement of two-dimensional three-axis magnetic field distribution in a specific area. Then, the experimental system was set up and realized the three-axis magnetic field measurement of 25 points within the 4 mm × 4 mm two-dimensional measurement range, and the resolution of each point is a square area with a side length of 0.8 mm. The proposed method based on the SERF atomic magnetometer can measure the triaxial magnetic field in the internal micro-regions in the magnetic field coil, magnetic shield, etc., helping the analysis and evaluation of the high-resolution magnetic field distribution.
The measurement of atomic spin polarization distribution in spin-exchange relaxation free (SERF) magnetometer is an important topic for improving the sensitivity and consistency of multi-channel magnetic field measurement applications. A novel spin polarization spatial distribution measurement method is presented based on the transient response of the magnetometer after modulating the pumped light with a chopper. Polarization is obtained by a slow-down factor based on the fast spin-exchange interaction effects. Longitudinal and transverse polarization distributions are measured simultaneously without interrupting the operation of the SERF status. Under different oscillating magnetic fields, the spin polarization is measured at the cell centroid. Residual magnetic field inside the magnetometer is obtained from the linear relationship between the precession frequency and the oscillating magnetic field. The one-dimensional polarization distributions in the x, y, and z axes are measured using a digital micromirror device with a resolution of 0.25 cm. The measurement results conform to the Lambert-Bier absorption law and the Gaussian distribution law. Furthermore, 7 × 7 two-dimensional spatial distribution measurements of polarization on the xy and yz planes are performed. Nonuniformity of 1.04 in the xy plane and 1.82 in the yz plane in the built magnetometer. Compared with other measurement methods, the distribution measurement method proposed is independent of optical depth and suitable for low polarization and high polarization applications. Based on the results of the proposed measurement method of spin polarization spatial distribution, further compensation can improve the application consistency of multi-channel magnetic field measurements and improve the sensitivity of single-channel differential measurements.
Abstract We present a design for a multi-channel optically pumped zero-field magnetometer utilizing a 200-μm-thick Rubidium vapor cell. The vapor cell and its housing are designed to reduce the minimal distance between a magnetic sample and the sensing volume to about 1 mm, to optimize the effective spatial resolution. The thin vapor cell, filled with 2 atm of nitrogen as a buffer gas reduces the volume across which the magnetic field is averaged. The vapor cell is fully illuminated by a single laser beam, and the transmitted light is imaged onto a 4 x 4 photodiode array, allowing for simultaneous measurement of a magnetic field distribution with up to 16 channels. The performance of the magnetometer is studied for all channels. It is shown that the sensor can operate in the spin-exchange relaxation-free regime with a projected photon-shot noise limited noise floor of about 1 pT/Hz1/2 for a sensitive voxel size of approximately 600 μm x 600 μm x 200 μm.
The ultrasensitive magnetometer has a vital importance in fundamental research and applications. Currently, the spin-exchange relaxation-free (SERF) atomic magnetometer has been reported with a sensitivity around the level of fT/Hz 1/2 . To enhance the sensitivity, a gradiometer configuration has usually been introduced to cancel the common-mode noise between two separate channels. However, the signal and response from different channels are not the same due to the attenuation of the pump beam. Here, we proposed a counter-propagating optical sideband pumping method to polarize the atoms, using the electro-optic modulator to modulate the single-pump beam, generating two symmetrically red- and blue-detuned sidebands of frequency. This scheme leads to a significant reduction of undesirable effects coming along with the optical pumping, such as light shifts and spatial inhomogeneity in atomic spin polarization. With the help of this pumping scheme, the two channels have the same magnetic response, and we have built a gradiometer atomic magnetometer with a sensitivity of 0.5 fT/Hz 1/2 ranging from 5 to 40 Hz. Our results propose the possibility of creating larger arrays of atomic magnetometers (AMs) with high sensitivity and spatial resolution based on single-vapor cells for magnetocardiography and magnetoencephalography imaging or searching for exotic spin-dependent interactions.
High-sensitivity multi-channel atomic magnetometers are described. Methods for operating multi-channel atomic magnetometers are also described. Moreover, devices incorporating a plurality of multi-channel atomic magnetometers are described. A multi-channel atomic magnetometer may use the spin-exchange relaxation-free (SERF) technique. A multi-channel atomic magnetometer may achieve multi-channel operation in a single module, reducing the cost of sensors. A multi-channel atomic magnetometer may be a 16-channel atomic magnetometer. A multi-channel atomic magnetometer may include a single large vapor cell including alkali-metal atoms and at least one buffer gas that restricts motion of atomic spins of the alkali-metal atoms, thereby making relatively small internal cell volumes act as a multiple independent local sensing channels. A multi-channel atomic magnetometer may include a broad pump beam that simultaneously polarizes all (or substantially all) of the alkali-metal atoms in each internal sensing volume of the vapor cell, and a broad probe beam that simultaneously measures magnetic fields at multiple sensing volumes with a photodiode array.
Multi-passed probe light can enhance the signal of atomic magnetometers by increasing the effective optical path length between the alkali metal atomic ensemble and the probe light, thereby strengthening the sensitivity. In recent years, multi-passed probe light has become an important method for improving the response signal and sensitivity of atomic magnetometers. To achieve biaxial magnetic field measurement while maintaining high sensitivity, a biaxial measurement spin-exchange relaxation-free (SERF) atomic magnetometer with a multi-passed probe light is proposed in this paper. The theoretical model and experimental advantages of using multi-passed probe light in longitudinal magnetic field modulation (Z-mode) SERF atomic magnetometers are analyzed. In this paper, a new model of output response of the Z-mode SERF atomic magnetometer based on multi-passed probe light is established, a compact reflective optical path is designed to increase the optical path between the probe light and the polarized alkali metal atomic ensemble, enhance the signal response, and achieve the suppression of low-frequency 1/f noise through longitudinal magnetic field modulation. Experimental results confirmed that the magnetic field sensitivity in the x- and y-axis of the multi-passed probe light configuration improved by 29% and 18%, respectively, compared to the single-pass configuration.