Atomic magnetometers with magnetic field modulation have emerged as pivotal sensors for biomagnetic measurements. However, challenges such as crosstalk between adjacent modulation fields and the complexity of signal circuitry become increasingly serious in the development of array-based equipment with the magnetometers, especially in the miniaturized atomic magnetometer. This paper proposes an all-optical, fully integrated fiber-coupled atomic magnetometer that employs pump beam modulation. A miniaturized atomic magnetometer with a volume of 10 cm³ has been designed, incorporating an active measurement area of 3 × 3 × 3 mm3. The magnetometer operates in the spinexchange relaxation-free (SERF) regime with an 87Rb vapor cell. An amplitude-modulated pump beam directly modulates the rubidium atomic ensembles, rather than the magnetic field modulation. The optical rotation angle is detected by an unmodulated probe beam oriented orthogonally to the pump beam. In light of the discontinuous pumping characteristics, we developed a modified theoretical model to clarify the output response of the proposed atomic magnetometer. The experimental results demonstrate that the new design achieves the same sensitivity as conventional magnetometer configurations with a smaller volume and without crosstalk of the magnetic field. This research highlights the significant potential for advancing the development of highly sensitive, miniaturized atomic magnetometers, making them particularly suitable for applications in magnetocardiography (MCG) and magnetoencephalography (MEG).
Optically pumped gradiometers have emerged as a promising tool for measuring extremely weak magnetic fields generated by nearby bio-magnetic sources, providing remarkable advantages such as high sensitivity, compact footprint, and the ability to operate in unshielded environments. However, existing gradiometer configurations often employ fixed baseline distances, which hinders the optimization of parameters such as baseline distance when dealing with magnetic sources of different sizes. Moreover, there is a lack of universal conclusions in current research regarding the optimal selection of baseline distance, measurement distance, and other parameters for various magnetic source types. To address this issue, we construct a dual-channel spin-exchange relaxation-free (SERF) gradiometer with an adjustable baseline ranging from 5 mm to 60 mm to investigate the relationships between the baseline distance of the gradiometer, the size of the magnetic field source, and the measurement distance, as well as their impact on the signal-to-noise ratio (SNR). By employing circular coils of different radii to simulate magnetic field sources, we measure the SNR of the gradiometer under the distance ranging from 40 mm to 95 mm and present normalized SNR curves that illustrate the relationship between the baseline distance, field source radius, and measurement distance. To ensure universal applicability, the specific distances are converted into multiples of the source radius. The results demonstrate that positioning the gradiometer closer to the source enhances its SNR, regardless of the source size. However, the optimal baseline distance varies depending on the source size, with smaller sources requiring relatively longer baselines to achieve better performance. We believe these findings can offer reliable evidence for optimizing gradiometer configurations in bio-magnetic measurements and other applications involving sources of different sizes
An in situ simultaneous measurement of magnetic coil constants and nonorthogonal angles method is proposed using the atomic magnetometer. Based on the transient response of the atomic spin polarization under the different magnetic fields, we establish the corresponding measurement model of magnetic coil constants and nonorthogonal angles through the relationship between the Larmor precession frequency and the external magnetic field. By this model, we experimentally obtained the coil constants of x , y, and z axes are, respectively, 9.04 ± 0.10, 8.94 ± 0.07, and 4.34 ± 0.02 nT / V in our system. The nonorthogonal angles are 89.04 deg between x axis and y axis, 88.60 deg between y axis and z axis, and 91.15 deg between z axis and x axis. This method can be used to simultaneously measure magnetic coil constants and nonorthogonal angles without relying on external instruments, which provides a basic guarantee for the accurate calculation sensitivity of spin-exchange-relaxation-free atomic magnetometers, especially for miniaturized atomic magnetometers.
We theoretically develop a method for maintaining the self-compensated state of a K-Rb21Ne comagnetometer, which is one of the core problems in optimizing the detection sensitivity of the comagnetometer to fundamental interactions and inertial rotation. The result of Rb21Ne coupling dynamics under transverse cosinusoidal magnetic field modulation can present a dispersive response with respect to the varying 21Ne nuclear magnetic field Bn, in which a monotonic interval can be used to monitor the drift of Bn. Furthermore, the result of Rb spin poparization evolution under the constraint of self-compensated-state maintenance exhibits a large enough time scale relative to Rb spin relaxation that it can be regarded as a quasi-static process, thus the adopted time-varying pump light intensity can be obtained using Rb equilibrium polarization. Accordingly, an implementation scheme is given. This method can not only compensate the drifting �", but also promote the system to return back to the original self-compensated state through manipulation of atomic polarization via time-varying pump light, which is useful in stabilizing the system performance.
We propose a modeling methodology tailored to predicting the wavelength and power output from a distributed Bragg reflector laser for use in quantum measurements. The relationship between power, wavelength, current, and temperature is acquired with a genetic algorithm (GA). The function set and termination set for GA are determined from the physical mechanisms of laser current, temperature, and output performance. To verify the validity of the method, measured data are divided into a training group and a test group. The test results show that our models can accurately predict the value of power and wavelength at the given current and temperature, with the RMSE of 13.4 μW and 6.0 × 10 − 5 nm, respectively. This method can help enhance the output performance of a laser.
The thermal effect problem is one of the key research issues in the design of semiconductor laser structures. The heat flow generated in the laser tube has a significant influence on the inherent characteristics of the structure. Thermal modal finite element analysis is an important method to study the influence of thermal load on the intrinsic properties of the structure. It is of great significance for the material selection and structural design of the laser. Based on the mechanical performance and temperature load requirements, this paper aims at the miniaturization of the overall structure. The internal thermal load is analyzed and applied. Based on this, the structure and structural parameters of the semiconductor laser are optimized.
We propose a far off-resonance laser frequency stabilization method that can accurately adjust the frequency lock points based on the Faraday rotation spectroscopy. The atomic magnetometer based on the spin-exchange relaxation-free (SERF) theory needs to stabilize the frequency of the probe laser on the detuning of several gigahertz (GHz) away from the resonance of the alkali metal atom, to reduce the absorption of the probe light by the alkali metal vapor cell. We propose a laser frequency stabilization method that can accurately adjust the frequency lock points using an acousto-optic modulator based on Faraday rotation spectroscopy. We reveal the principles of the method and simulate the new Faraday rotation spectra. Besides, we study the effect of the amount of frequency shift of the acousto - optic modulator and the temperature of the alkali metal vapor cell on the frequency lock points of the spectra, and give the formula for calculating the frequency point. Our proposed laser frequency stabilization method can stabilize the laser frequency on the detuning of several gigahertz (GHz) away from the resonance of the alkali metal atom and can adjust the frequency lock points quickly and accurately. This method can be used in atomic magnetometer, degenerate Raman sideband cooling (DRSC) and two photon excitation of Rydberg states.
Distributed feedback laser is widely used as the pump beam and probe beam in atomic physical and quantum experiments. As the frequency stability is a vital characteristic to the laser diode in these experiments, a saturated absorption frequency stabilization method assisted with the function of current and frequency is proposed. The relationship between the current and frequency is acquired based on the genetic programming (GP) algorithm. To verify the feasibility of the method, the frequency stabilization system is comprised of two parts that are modeling the relation between the current and frequency by GP and processing the saturated absorption signal. The results of the frequency stabilization experiment proved that this method can not only narrow the frequency searching range near the atomic line center but also compensate for the phase delay between the saturated absorption peak and the zero crossing point of the differential error signal. The reduced phase delay increases the locking probability and makes the wavelength drift only 0.015 pm/h, which converted to frequency drift is 7 MHz/h after frequency locking on the Rb absorption line.
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