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Scientific Reports

Sensitive determination of the spin polarization of optically pumped alkali-metal atoms using near-resonant light

Zhichao Ding, Xingwu Long, Jie Yuan, Zhenfang Fan, Hui Luo

Published Sep 6, 2016• 26 citations
Publisher

Abstract

A new method to measure the spin polarization of optically pumped alkali-metal atoms is demonstrated. Unlike the conventional method using far-detuned probe light, the near-resonant light with two specific frequencies was chosen. Because the Faraday rotation angle of this approach can be two orders of magnitude greater than that with the conventional method, this approach is more sensitive to the spin polarization. Based on the results of the experimental scheme, the spin polarization measurements are found to be in good agreement with the theoretical predictions, thereby demonstrating the feasibility of this approach.

DOI
10.1038/srep32605

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Journal of Physics B Atomic Molecular and Optical Physics•Apr 29, 2021•3 citations
A new method to measure the spin polarization of optically pumped alkali-metal atoms is demonstrated. Unlike the conventional method using far-detuned probe light, the near-resonant light with two specific frequencies was chosen. Because the Faraday rotation angle of this approach can be two orders of magnitude greater than that with the conventional method, this approach is more sensitive to the spin polarization. Based on the results of the experimental scheme, the spin polarization measurements are found to be in good agreement with the theoretical predictions, thereby demonstrating the feasibility of this approach.
Optically pumped alkali metal atoms currently provide a sensitive solution for magnetic microscopic measurements. As the most practicable plan, Faraday rotation of linearly polarized light is extensively used in spin polarization measurements of alkali metal atoms. In some cases, near-resonant Faraday rotation is applied to improve the sensitivity. However, the near-resonant linearly polarized probe light is elliptically polarized after passing through optically pumped alkali metal vapor. The ellipticity of transmitted near-resonant probe light is numerically calculated and experimentally measured. In addition, we also analyze the negative impact of elliptical polarization on Faraday rotation measurements. From our theoretical estimate and experimental results, the elliptical polarization forms an inevitable error in spin polarization measurements.
Abstract A practical method to measure the spin polarization of optically pumped alkali atoms is demonstrated. In order to realize transverse measurement, the transverse spin component of spin-polarized alkali atoms is created by a rotating exciting magnetic field, and detected using the optical rotation of a near-resonant probe beam for realizing a high detection sensitivity. The dependency of the optical rotation on the spin polarization of 133 Cs atoms is derived theoretically and verified experimentally. By changing the direction of the rotating magnetic field, we realize the transverse measurement of the spin polarization of 133 Cs atoms in either ground-state hyperfine level.
High sensitivity measurements of inertia and magnetic field could be achieved by utilizing a category of devices, which manipulate the atomic spins in the spin-exchange-relaxation-free regime. The alkali cell which contains the alkali metal vapor is used to sense magnetic field and inertia. The atomic number density of alkali vapor and the polarization of alkali metal vapor are two of the most important parameters of the cell. They play an important role in the research on atomic spins in the spin-exchange-relaxation-free regime. Besides, optical polarization plays an important role in quantum computing and atomic physics. We propose a measurement of alkali vapor polarization and alkali number density by detecting the optical rotation in one system. This method simplifies existing experimental equipment and processes. A constant bias magnetic field is applied and the Faraday rotation angle is detected by a bunch of the probe beam to deduce alkali-metal density. Then the magnetic field is closed and a bunch of the pump laser is utilized to polarize alkali-metal. Again, the probe beam is utilized to obtain the polarization of alkali metal. The alkali density obtained at first is used to deduce the polarization. This paper applies a numerical method to analyze the Faraday rotation and the polarization rotation. According to the numerical method, the optimal wavelength for the experiment is given. Finally, the fluctuation of magnetic field and wavelength on signal analysis are analyzed.
The existence of an approximately uniform and unsaturated electron spin polarization distribution within a high-density alkali-metal vapor is considered of great importance for significantly improving the response amplitude and sensitivity properties of an atomic magnetometer. However, when a high-density alkali-metal vapor is formed, the optical depth is much larger than the value of one, resulting in the electron spin polarization gradient. In this work, it was demonstrated from both numerical simulations and experimental points of view, that by replacing the resonant pumping light with two off-resonant pumping light sources, the signal amplitude of the magnetometer can be doubled. By using this approach, the electron spin polarization gradient can be significantly suppressed and the sensitivity can be improved by more than 10%. The proposed scheme is generally applicable to various optical pumping high-density alkali-metal vapor systems, where a uniform electron spin polarization distribution is required, such as optical pumping co-magnetometers and atomic gyroscopes.
Abstract The polarization of light affected by the birefringence of optical elements, such as vapor cell walls, mirrors, and windows, may introduce systematic errors that can be minimized by precisely measuring and correcting the light polarization with a highly sensitive atomic polarimeter. In high precision measurements, it is necessary to measure the light polarization with a high precision where the light interacts with atoms. However, it is inconvenient or even impossible to use the presented method to measure the light polarization, for example, in a cell or cavity. We present a precise and relatively straightforward method to measure the light polarization based on a cesium (Cs) atomic magnetometer configuration. The pump-probe scheme is involved in our experiment. The pump light polarizes atomic spins and the probe light measures the spins polarization. The optical rotation of the probe light significantly depends on the pump light ellipticity, which can be used to measure the light polarization with a high precision. In our work, we present a method to measure the pump light ellipticity with a sensitivity of 2.1 × 10 −8 rad Hz −1/2 for linearly polarized light, which has approximately an order of magnitude improvement than previous research results.