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Third Asia Pacific Optical Sensors Conference

An electro-optic modulator detection method in all optical atomic magnetometer

Yanhui Hu, Xuejing Liu, Yang Li, Ming Ding

Published Jan 1, 2016• 3 citations
Publisher

Abstract

An electro-optic modulator (EOM) detection method is demonstrated to detect the optical atomic precession in the Spin-Exchange Relaxation Free (SERF) atomic magnetometer, which achieved a sensitivity of ~30 fT/Hz1/2 at the calibration frequency of 30Hz. The SERF atomic magnetometer based on EOM presents several advantages, such as simple structure, no magnetic shielding, moderate thermal effect and high measurement accuracy. It is demonstrated to be feasible for the compactness and simplicity of atomic magnetic field measurement devices in the future.

DOI
10.1364/apos.2016.tu3a.6

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An electro-optic modulator (EOM) detection method is demonstrated to detect the optical atomic precession in the Spin-Exchange Relaxation Free (SERF) atomic magnetometer, which achieved a sensitivity of ~30 fT/Hz1/2 at the calibration frequency of 30Hz. The SERF atomic magnetometer based on EOM presents several advantages, such as simple structure, no magnetic shielding, moderate thermal effect and high measurement accuracy. It is demonstrated to be feasible for the compactness and simplicity of atomic magnetic field measurement devices in the future.
Abstract We present an ultrahigh-sensitivity electro-optic modulator (EOM) detection method for detecting the atomic Larmor precession in an all-optical K–Rb hybrid atomic magnetometer operating in the spin-exchange relaxation-free regime. A magnetic field sensitivity of ~10 f T Hz −1/2 has been achieved by optimizing the probe laser parameters and the EOM modulation conditions, which is comparable to that with the Faraday modulation method and has a better performance than the balanced polarimetry method in the low frequency range. The EOM detection method in the atomic magnetometer presents several advantages, such as simple structure, no extra magnetic noise, moderate thermal effect, high measurement sensitivity and reliable stability. It is demonstrated to be feasible for the improved compactness and simplicity of atomic magnetic field measurement devices in the future.
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.
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.
Spin-exchange-relaxation-free (SERF) atomic magnetometer is the most sensitive magnetic detector in the world at present due to the fact that the broadening of spin-exchange collision is eliminated by operating at high alkali-mental density and low magnetic field. On that condition, the precession frequency of high-density alkali vapor becomes a constant fractional value of Larmor frequency, and the width of magnetic-resonance line gets narrower. This paper analyzes the principle of SERF regime and proposes an innovation based on measuring the slowing-down Larmor frequency directly instead of the complicated conventional method based on the width of magnetic resonance line. We calculated and simulated the slowing-down precession frequency and linewidth of magnetic resonance on certain conditions. The experimental results have verified that the method is valid to identify the regime of SERF of atomic magnetometer via detecting the slowing-down precession frequency.
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.
Ultra-sensitive multi-channel optically pumped atomic magnetometers based on the spin-exchange relaxation-free (SERF) effect are powerful tools for applications in the field of magnetic imaging. To simultaneously achieve ultra-high spatial resolution and ultra-high magnetic field sensitivity, we proposed a high-resolution multi-channel SERF atomic magnetometer for two-dimensional magnetic field measurements based on a digital micro-mirror device (DMD) as the spatial light modulator for a single vapor cell. Under the optimal experimental conditions obtained via spatial and temporal modulation of the probe light, we first demonstrated that the average sensitivity of the proposed 25-channel magnetometer was approximately 25fT/Hz 1/2 with a spatial resolution of 216µm. Then, we measured the magnetic field distribution generated by a gradient coil and compared the experimentally obtained distributions with those calculated via finite element simulation. The obtained g value of 99.2% indicated good agreement between our experimental results and the theoretical calculations, thereby confirming that our proposed multi-channel SERF magnetometer was effective at measuring magnetic field distributions with an ultra-high spatial resolution.