The sensitivity of existing all-optical atomic magnetometers is significantly compromised due to the simultaneous influence of optical parameters on both optical pumping and optical modulation of atoms. The tight interlinkage of these processes poses challenges for their individual optimization, thereby restricting the achievable sensitivity. To address this issue, we developed a comprehensive optical modulation analytical model that fully considers the effects of dynamic optical pumping. Building upon this model, we introduced a multi-objective optimization method for optical parameters, leading to minimal non-sensitive axis crosstalk and optimal sensitivity. Experimental results demonstrated a femtotesla all-optical spin-exchange relaxation-free magnetometer with sensitivities of 2 fT/Hz1/2 along the y-axis and 4 fT/Hz1/2 along the x-axis, respectively. This advancement surpasses the sensitivity of existing optically modulated magnetometers and bears profound implications for the advancement and application of arrayed magnetometers.
The sensitivity of existing all-optical atomic magnetometers is significantly compromised due to the simultaneous influence of optical parameters on both optical pumping and optical modulation of atoms. The tight interlinkage of these processes poses challenges for their individual optimization, thereby restricting the achievable sensitivity. To address this issue, we developed a comprehensive optical modulation analytical model that fully considers the effects of dynamic optical pumping. Building upon this model, we introduced a multi-objective optimization method for optical parameters, leading to minimal non-sensitive axis crosstalk and optimal sensitivity. Experimental results demonstrated a femtotesla all-optical spin-exchange relaxation-free magnetometer with sensitivities of 2 fT/Hz1/2 along the y-axis and 4 fT/Hz1/2 along the x-axis, respectively. This advancement surpasses the sensitivity of existing optically modulated magnetometers and bears profound implications for the advancement and application of arrayed magnetometers.
The spin-exchange relaxation-free (SERF) atomic magnetometers exhibit ultrahigh sensitivity for the magnetic field measurement, and their performance is further enhanced through zero-field parameter modulation. However, this modulation introduces additional parameter coupling that limits the performance of magnetometers in multi-axis measurement. In this paper, we develop a modified dual-axis output equation based on the nonlinear interaction between the optical pumping rate and modulation field amplitude, mediated by the spin-exchange relaxation and polarization. We employ a multi-objective optimization algorithm incorporating the implicit constraints among these parameters to enable efficient, simultaneous optimization of both the pump rate and modulation amplitude. Experimental results show that under optimal parameters obtained by the algorithm, the dual-axis signal responses improve by approximately 20% and 30% over conventional optimization methods, achieving 2.5 fT/Hz1/2magnetic measurement sensitivities for the y-axis and 4.0 fT/Hz1/2for the x-axis, respectively.
Abstract High-sensitivity triaxial magnetic field measurements are crucial in various scientific and industrial applications, with spin-exchange relaxation-free (SERF) atomic magnetometers (AMs) standing out for their exceptional sensitivity. However, conventional methods for achieving triaxial measurements in SERF magnetometers typically involve multiple modulated magnetic fields, which introduce crosstalk challenges in array-based configurations. We propose a static bias magnetic field assisted optical modulation triaxial AM to address this limitation. In this configuration, the detuned circularly polarized light is utilized to achieve synchronous modulation of the fictitious magnetic field and pumping rate while incorporating a static bias magnetic field to generate a transverse projection component. We develop a comprehensive triaxial response model that fully considers the effects of the longitudinal spin polarization deflection. Building upon this model, we derive the relationship between the transverse spin component and the triaxial magnetic field and introduce parameter optimization methods to obtain optimal parameters, thus enabling triaxial measurements of 12 fT Hz −1/2 , 10 fT Hz −1/2 , and 15 fT Hz −1/2 along the x-, y -, and z -axes. Our approach offers significant advantages over existing methods, particularly in minimizing crosstalk and mitigating spin-exchange relaxation introduced by multiple modulated magnetic fields. Moreover, the effective detection of simulated magnetocardiography signals highlights the practical applicability and reliability of the proposed method in real-world scenarios.
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 cross-talk effect, achieved by applying a rotating modulation field and using of the negative feedback. Operating in the dual-axis closed-loop mode with a miniature 4 × 4 × 4 mm 87Rb cell, we achieve magnetic field sensitivity of 20 fT/Hz1/2 and a bandwidth of 1.8 kHz. In addition to the experimental study of the sensitivity and bandwidth, we perform a theoretical analysis to 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 cross-talk 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 the noninvasive biomagnetic imaging.
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.
Elliptically polarized atomic magnetometers (AMs) offer high sensitivity and compactness by using a single laser beam to polarize atoms and detect optical rotation angles. However, their sensitivity advantage over optical absorption-based AMs has not been sufficiently demonstrated. This is because the optical parameters significantly affect the pumping and probing processes, leading to parameter coupling when both processes are optimized simultaneously. Such coupling presents a considerable challenge for achieving simultaneous parameter optimization, ultimately limiting the achievable sensitivity. In this study, we developed a modified input–output model for a magnetometer, based on which an optical parameter decoupling and optimization method is proposed. Our method enables us to obtain the optimal optical parameters simultaneously, including the ellipticity, intensity, and frequency of light. Consequently, a sensitivity of 6 fT/Hz1/2 was achieved using a4×4×4mm3 87Rb vapor cell (an effective volume of 0.027 cm3). This work offers an efficient strategy to achieve higher sensitivity using single-beam miniaturized AMs, contributing significantly to promote biomagnetism research.