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 fT/Hz1/2 at 30 Hz and 60 fT/Hz1/2 at 10 kHz. Meanwhile, the AM SERF magnetometer with DC demodulation presents the same sensitivity as a traditional DC SERF magnetometer (6 fT/Hz1/2 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.
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 fT/Hz1/2 at 30 Hz and 60 fT/Hz1/2 at 10 kHz. Meanwhile, the AM SERF magnetometer with DC demodulation presents the same sensitivity as a traditional DC SERF magnetometer (6 fT/Hz1/2 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.
Emerging quantum sensing devices namely atomic magnetometers have become promising candidate for future biomagnetism imaging. However, the limitation of detection bandwidth exists a major drawback for devices of this kind. Conventional approaches, including transverse magnetic field modulation and close-loop control, have seen challenging tradeoffs between size, resolution and bandwidths. In this study, a wide bandwidth zero-field magnetometer with a miniaturized light source has been developed for alternating current (AC) magnetic field detection. A dual-beam Spin-Exchange Relaxation-Free (SERF) magnetometer employing a 4×4×4mm3 alkali metal vapor cell achieves a bandwidth of 188 Hz. This represents a threefold increase in bandwidth compared to non-modulated mode. The sensitivity under modulated mode demonstrated a sensitivity of 55fT/Hz1/2within the frequency range of 10-188Hz. Our results also demonstrated that the sensitivity is constrained by relaxation induced by the modulation of pumping source, so possible tradeoffs can be made based on various applications. The proposed method provides novel approach for bandwidth extension of atomic magnetometers which further pave the way for future applications including magnetoencephalography (MEG), particularly in reducing magnetic noise crosstalk and enhancing spatial resolution.
Spin-exchange relaxation-free (SERF) magnetometers enable femtotesla-level bio-magnetic imaging, yet their scalability into high-density arrays is impeded by inter-sensor crosstalk arising from conventional magnetic-field modulation. While optical amplitude modulation offers a crosstalk-free alternative, its resonance mechanisms within the SERF regime remain unexplored. Here, we report a dual-resonance mechanism induced by amplitude-modulated light in a SERF magnetometer. Our theoretical model characterizes this behavior as the coexistence of a central zero-field resonance and symmetric parametric resonances at high atomic densities, in excellent agreement with experimental measurements. Systematic temperature and pump-power sweeps reveal the evolution of the dual-resonance profile, demonstrating that high alkali density sharpens and amplifies the zero-field resonance, whereas strong optical pumping restores the dominance of parametric resonances. Exploiting these distinct resonances, we utilize the parametric component to extract the slowing-down factor and spin polarization, which allows in situ coil calibration in both probe and pump channels with errors below 0.5%. In contrast, operation on the zero-field resonance significantly suppresses long-term drifts compared with DC detection and yields a sensitivity of 4.96 fT/Hz 1/2 . Ultimately, these findings elucidate the modulation physics within the SERF regime and establish a crosstalk-free framework that paves the way for high-precision bio-magnetic arrays.
The spin-exchange relaxation-free (SERF) atomic magnetometer (AM) has vital importance in advanced research and has been widely applied in different fields. To improve the sensitivity and robustness of SERF magnetometers, understanding the relaxation mechanism is a significant approach. By controlling the amplitude and direction of external magnetic fields, and switching statuses of the pump and probe laser beam, we measured both the transverse and longitudinal relaxation rate in two experimental methods, respectively, and obtained the Larmor precession frequency, the spin-exchange relaxation rate, the spin-destruction relaxation rate, and the relaxation rate due to collisions between atoms and vapor cell walls. All experimental results are verified with the theoretical calculations. The final longitudinal relaxation rate of our magnetometer is 53 Hz. Furthermore, we measured the sensitivity of our SERF magnetometer reaching 5 fT/Hz1/2 from 5 to 70 Hz after differential measurement with the 3-dB bandwidth of 70 Hz. Our work helps to improve the detection capability of SERF magnetometers, providing performance assurance for searching for exotic spin-dependent interactions and applications, including magnetoencephalograms and magnetocardiograms.
Spin-exchange relaxation-free (SERF) atomic magnetometers are the promising non-cryogenic sensors to potentially replace the superconducting quantum interference device (SQUID) in the ultra-weak magnetic-field measurements. Although the SERF magnetometers have achieved a sensitivity of sub-femtotesla, the bandwidth is limited at a narrow range. In this work, we developed a closed-loop SERF magnetometer under proportional-integral (PI) control, the bandwidth could be adaptively tuned and extended above 1.2 kHz. A nearly 40-fold enhancement of the typical bandwidth was achieved in comparison with the open-loop system and the sensitivity was maintained at 15 fT/Hz1/2from 30 Hz to 750 Hz. Moreover, the magnetic field dynamic range could also be greatly improved. This proposed atomic magnetometer with higher bandwidth, sensitivity, and dynamic range has a good prospect in developing a compact, portable, and non-cryogenic magnetic field sensor and may find more applications in biomedical, nuclear magnetic resonance, and fundamental physics research.
Atomic magnetometers are widely acknowledged as one of the most sensitive devices for magnetic field measurement. Our study presents a novel method that enables bandwidth expansion of single-beam magnetometers in the spin-exchange relaxation-free regime. This method bases on increasing the modulation amplitude of magnetic field combining with negative feedback with proportional gain. Through our method, the magnetometer’s total relaxation rate is moderately increased by elevating modulation amplitude and frequency, and correspondingly, the detection bandwidth experiences dramatic improvement from 230 Hz to 1380 Hz. The application of negative feedback with proportional gain further increases this bandwidth to higher than 4 kHz, which is over 17 times of its original value. The sensitivity of the magnetometer under this condition is measured as 25 fT/Hz1/2for open-loop scheme and 35 fT/Hz1/2for closed-loop scheme. Comparatively, the sensitivity measured on conventional conditions in our experiment is 12 fT/Hz1/2. This approach offers a profitable trade-off that extraordinary expansion of detection bandwidth can be acquired with the price of a little sensitivity loss. Our method is advantageous for miniaturization of atomic magnetometers as no extra hardware is added, which is of special interest for applications including biomagnetic measurement where large detection bandwidth is sometimes in need.
We demonstrate that the use of negative feedback extends the detection bandwidth of an atomic magnetometer in a spin-exchange relaxation free (SERF) regime. A flat-frequency response from zero to 190 Hz was achieved, which is nearly a three-fold enhancement while maintaining sensitivity, 3 fT/Hz1/2 at 100 Hz. With the extension of the bandwidth, the linear correlation between measured signals and a magne-tocardiographic field synthesized for comparison was increased from 0.21 to 0.74. This result supports the feasibility of measuring weak biomagnetic signals containing multiple frequency components using a SERF atomic magnetometer under negative feedback.