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Applied Optics

Broadband optically pumped NMR gyroscope technique based on Gaussian white noise phase modulation

Tong Huo, Jianhua Yang, Zhihang Zhang, Zhiguo Wang, Dapeng Han, Lijun Miao, Dengwei Zhang

Published Aug 22, 2025• 0 citations
Publisher

Abstract

This work proposes an optical pumping strategy based on a broadband laser to overcome the problem of atomic spin polarization gradients and sensitivity to optical frequency noise in NMR gyroscopes. A band-limited Gaussian white noise radiofrequency signal is applied to a lithium niobate electro-optic phase modulator to do this. A narrow linewidth laser maintains its frequency stability while uniformly broadening its spectrum to the hundreds of MHz range. Compared to unmodulated pumping, the proposed scheme enhances the uniformity of rubidium spin polarization by approximately 10%, reaching a measured value of 92.8%. Additionally, the sensitivity of the inert gas precession signal to optical frequency noise is reduced by half. This scheme can be extended to other atomic sensors requiring higher uniform spin polarization distributions and provides a promising way to achieve high-stability, low-noise NMR gyroscope systems.

DOI
10.1364/ao.575074

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This work proposes an optical pumping strategy based on a broadband laser to overcome the problem of atomic spin polarization gradients and sensitivity to optical frequency noise in NMR gyroscopes. A band-limited Gaussian white noise radiofrequency signal is applied to a lithium niobate electro-optic phase modulator to do this. A narrow linewidth laser maintains its frequency stability while uniformly broadening its spectrum to the hundreds of MHz range. Compared to unmodulated pumping, the proposed scheme enhances the uniformity of rubidium spin polarization by approximately 10%, reaching a measured value of 92.8%. Additionally, the sensitivity of the inert gas precession signal to optical frequency noise is reduced by half. This scheme can be extended to other atomic sensors requiring higher uniform spin polarization distributions and provides a promising way to achieve high-stability, low-noise NMR gyroscope systems.
An optical pumping scheme is proposed for reducing the gradient of electron spin polarization and suppressing light source noise in a spin-exchange relaxation-free magnetometer. This is achieved by modulating only the phase of a narrow-linewidth pump light field with external Gaussian noise. Compared to the absence of phase modulation, the uniformity of electron spin polarization was improved by over 40%, and the light-frequency noise suppression ratio of the magnetometer was enhanced by 4.3 times. Additionally, the response of the magnetometer was increased by 54%, resulting in a sensitivity of 0.34 fT/Hz 1/2 at 30 Hz. The applicability of this scheme can extend to other optical pumping experiments involving large atom ensembles requiring uniform electron spin polarization distribution, which is beneficial for developing ultra-high sensitivity and high stability magnetometers essential for magneto-cardiography and magneto-encephalography research applications.
A high-sensitivity atomic magnetometer based on broad linewidth laser pumping is demonstrated. The broad linewidth laser was obtained by broadening a narrow linewidth laser utilizing an external phase modulator driven by a pseudo-random-bit-sequence (PRBS) waveform. This ingenious optical pumping scheme can significantly enhance the signal response and suppress light shift noise, as well as can reduce the gradient of electron spin polarization and improve the stability of magnetometers. Compared with a narrow linewidth laser pumping scheme, the response of the magnetometer is increased by 56%, experimentally. The relative polarization gradient is reduced from 9.8%/cm to better than 4%/cm by setting PRBS with a bit rate of 16 GHz. This scheme can also be applied to many other fields such as noninvasive bio-magnetic imaging and atomic spin gyroscopes.
A hybrid optical pumping method employing a broad linewidth laser is proposed to enhance spin coherence and suppress virtual magnetic field noise in atomic magnetometers. The central frequency of broad linewidth laser is tuned to the resonance peak of the alkali-metal atoms D1 line. Its multiple frequency components suppress AC-Stark shift fluctuations caused by pumping laser frequency variations, thereby reducing virtual magnetic field noise. In addition, these components decrease the average optical absorption cross-section, improving the uniformity of atomic spin polarization, further enhancing spin coherence and extending transverse relaxation time. Experimental results show that, compared with narrow linewidth pumping, the proposed method suppresses virtual magnetic field noise by 17.95% to 34.50%, and increases the magnetometer response by 1.62% to 30.31% at 5 Hz. The average sensitivity within the frequency range of 1-20 Hz is improved to 0.158 fT/Hz 1/2 , representing a significant enhancement of 30.70% compared to narrow linewidth pumping.
Abstract Atomic spin comagnetometers based on the spin-exchange relaxation-free (SERF) effect offer significant potential for inertial sensing and support the development of long-endurance, high-precision navigation technologies. However, limited nuclear spin polarization constrains the long-term stability of these systems. Here, a flat-top optical pumping configuration is introduced for SERF comagnetometers, expanding the uniform-intensity region of the beam to approximately 62 % , which enhances atomic polarization by around 19 % and improves magnetic noise suppression by 32 % . Experimental results demonstrate notable improvements in both sensitivity and long-term stability, highlighting the effectiveness of flat-top beams in overcoming atomic polarization uniformity limitations and advancing SERF co-magnetometer performance.
The paper presents the results of the development of a laser-optical system for atomic interferometer based on rubidium atoms cooled to sub-Doppler temperatures. The laser-optical scheme was created to ensure the processes of cooling, pumping, and detecting atoms involved in interferometric measurements of free-fall acceleration. The system utilizes frequency doubled fiber lasers and broadband fiber electro-optical modulators. The choice of fiber lasers is driven by their high efficiency, narrow spectral line, low phase noise levels, as well as ease of operation and reliability. Laser frequency stabilization was carried out using modulation transfer spectroscopy and optical phase-locking methods. Experimental setups were described that allow the generation of multichromatic radiation and minimize spontaneous scattering by detuning from excited levels. It was noted that the design provides a full set of optical frequencies necessary for Raman spectroscopy. The amplitudes of frequency fluctuations of the cooling and pumping lasers were studied. It was shown that the implemented laser-optical system can ensure continuous operation of an atomic interferometer based on clouds of cold rubidium atoms, and an assessment of the fundamental sensitivity limit was conducted.
Optical pumping of an atomic vapor with low-power lasers often results in low pumping efficiency because of the narrow laser linewidth. Broadening of the laser spectrum by frequency modulation (FM) ensures the contribution of atoms from all velocity classes. We numerically evaluate the difference between the population enhancement for a vapor pumped with a modulated laser and that with a nonmodulated laser. The most efficient modulation scheme among those considered is FM with narrow-band Gaussian noise. The achieved optical pumping enhancement depends on laser linewidth and available power.