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In-situ measurement of magnetic field gradient in a magnetic shield by a spin-exchange relaxation-free magnetometer |
| Fang Jian-Cheng (房建成)a, Wang Tao (王涛)a, Zhang Hong (张红)b, Li Yang (李阳)a, Cai Hong-Wei (蔡洪炜)a |
a School of Instrument Science and Opto-Electronics Engineering, Science and Technology on Inertial Laboratory, Beihang University, Beijing 100191, China;
b School of Instrument Science and Engineering, Southeast University, Nanjing 210096, China |
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Abstract A method of measuring in-situ magnetic field gradient is proposed in this paper. The magnetic shield is widely used in the atomic magnetometer. However, there is magnetic field gradient in the magnetic shield, which would lead to additional gradient broadening. It is impossible to use an ex-situ magnetometer to measure magnetic field gradient in the region of a cell, whose length of side is several centimeters. The method demonstrated in this paper can realize the in-situ measurement of the magnetic field gradient inside the cell, which is significant for the spin relaxation study. The magnetic field gradients along the longitudinal axis of the magnetic shield are measured by a spin-exchange relaxation-free (SERF) magnetometer by adding a magnetic field modulation in the probe beam's direction. The transmissivity of the cell for the probe beam is always inhomogeneous along the pump beam direction, and the method proposed in this paper is independent of the intensity of the probe beam, which means that the method is independent of the cell's transmissivity. This feature makes the method more practical experimentally. Moreover, the AC-Stark shift can seriously degrade and affect the precision of the magnetic field gradient measurement. The AC-Stark shift is suppressed by locking the pump beam to the resonance of potassium's D1 line. Furthermore, the residual magnetic fields are measured with σ+- and σ--polarized pump beams, which can further suppress the effect of the AC-Stark shift. The method of measuring in-situ magnetic field gradient has achieved a magnetic field gradient precision of better than 30 pT/mm.
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Received: 03 November 2014
Revised: 24 December 2014
Accepted manuscript online:
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PACS:
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07.55.Ge
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(Magnetometers for magnetic field measurements)
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07.55.-w
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(Magnetic instruments and components)
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41.20.Gz
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(Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems)
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32.60.+i
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(Zeeman and Stark effects)
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| Fund: Project supported by the National Natural Science Foundation of China (Grant Nos. 61227902, 61374210, and 61121003). |
Corresponding Authors:
Wang Tao
E-mail: wangtao@buaa.edu.cn
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| About author: 07.55.Ge; 07.55.-w; 41.20.Gz; 32.60.+i |
Cite this article:
Fang Jian-Cheng (房建成), Wang Tao (王涛), Zhang Hong (张红), Li Yang (李阳), Cai Hong-Wei (蔡洪炜) In-situ measurement of magnetic field gradient in a magnetic shield by a spin-exchange relaxation-free magnetometer 2015 Chin. Phys. B 24 060702
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