Magnetic field gradients affect numerous modern sensitive measurements and physics studies using atomic ensemble, resulting in the loss of coherence. In some cases, the presence of small gradients can reduce the performance significantly. In this study, we propose an effective in situ method to compensate the triaxial magnetic field gradient for atomic magnetometers, based on multichannel atomic signals in one vapor cell. We design two novel gradient coils by solving closed-form equations to improve the accuracy and efficiency of compensation. We demonstrate the performance of the compensation method in a spin-exchange relaxation-free atomic magnetometer, which reduces the magnetic linewidth by 4.2%–7.6% under the same conditions at a compensation resolution of 50 pT/cm. The proposed coils generate gradients only along two axes and achieve triaxial decoupling, which compensates for the gradient completely without iteration. Our results may aid in suppressing atomic spin relaxations due to magnetic field gradients in several modern measurements and improve their performance, such as the detection of electric dipole moments, ultralow-field nuclear magnetic resonance, and biomagnetism.

The calibration results of the triaxial coils affect the atomic magnetometer’s measurement sensitivity. For precise in-situ calibration, we firstly studied the transient atomic dynamics of a dual beam SERF atomic magnetometer under alternating magnetic fields. We obtained the corresponding dynamic free-induction decay (FID) curves by alternately applying square wave signals to the x -, y - and z -axis coil, and then extracted the precession frequencies by fast Fourier transform (FFT) to achieve a decoupled calibration of the triaxial coil constants. Our calibration results were in better agreement under different experimental conditions than traditional parameter fitting methods with a relative error of less than 1.5% compared to conventional fluxgate calibration methods. Furthermore, we simultaneously measured nonorthogonal angles between each pair of axes: x-y , y-z , and z-x , respectively, which are used to correct the magnetic fields error. This method is suitable for coil calibration and nonorthogonal correction of integrated and miniaturized dual beam magnetometers.

This article presents a method for measuring the spin polarization of spin-exchange relaxation-free (SERF) atomic magnetometers at extremely large optical depths. Due to the slowing-down effect, spin polarization can be extracted by measuring the slowing-down factor extracted from the precession frequency. However, this technique is limited by a significant error in the regime of extremely large optical depths, where the pump beam intensity for achieving the optimal spin polarization of alkali atoms is significantly increased. We observed that the instantaneous precession frequency measured in the regime where the spin-exchange rate is not much larger than the Larmor frequency was no longer a constant but varied with the pump beam intensity. Thus, a method for measuring spin polarization based on the ratio of the precession frequency to the measured instantaneous precession frequency is proposed. Based on the proposed method, the spin polarization at a temperature of 473 K and an optical depth of 64 is measured. The measurement results were in accordance with theoretical analysis. The expanded uncertainties of the experimental results varied between 1.8% and 9.6%. The proposed method is also applicable to other atomic devices operated in the SERF regime with extremely large optical depths, such as co-magnetometers and atomic spin gyroscopes.

Ultranarrow linewidth fiber lasers have good application prospects in high-precision spontaneous Raman detection systems due to their excellent frequency stability and low phase noise characteristics. This study first presents a theoretical derivation of the influence between laser linewidth and Raman detection performance, focusing on signal-to-noise ratio. Subsequently, a self-developed ultranarrow linewidth fiber laser, featuring a linewidth of 650 Hz, is utilized to experimentally validate the influence of laser linewidth on signal-to-noise ratio. The results demonstrate that reducing the laser linewidth from 200 kHz to 650 Hz improves the signal-to-noise ratio of mid frequency spectra by a factor of 1.58. This work offers both a theoretical foundation and experimental evidence to support the optimization of Raman system design.

In this paper, we systematically established a chirp modulation theoretical model for spectral focusing coherent anti‐Stokes Raman scattering technology (SF‐CARS). Through in‐depth analysis of the dispersion characteristics of fiber optic dispersion and grating pairs, the control mechanism of dispersion effect on the time frequency characteristics of laser pulses is elucidated, and the influence of laser pulse parameters on spectral resolution and signal‐to‐noise ratio (SNR) is revealed. Through theoretical optimization of precise chirp modulation, we improved the spectral resolution of the SF‐CARS system to 6.7 cm ⁻¹ and simultaneously enhanced the SNR to 340, achieving a concurrent improvement in both resolution and detection sensitivity. With the improvement of spectral resolution and SNR of SF‐CARS, its application boundaries for studying dynamic processes will be further expanded.