Source: http://aoot.osa.org/oe/abstract.cfm?uri=oe-27-6-8037
Timestamp: 2019-04-20 04:26:34+00:00

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Optically pumped magnetometers (OPMs) that are equipped with hybrid cells of K and Rb have been studied for improving their sensitivity and biomagnetic field measurements. The densities of the two alkali metal atoms and their density ratio are especially important for hybrid OPMs. In this study, we fabricated five hybrid cells using different K and Rb atom densities and measured the output signal intensities by controlling their cell temperatures. The output signal intensity of OPMs has different temperature characteristics depending on the density ratios of K and Rb atoms. The densities of the two atoms at any temperature were estimated based on the Raoult’s law, and we compared the experimental results with the calculated results based on the Bloch equations. Furthermore, the numerical calculations that were obtained based on the Bloch equation by incorporating a relaxation term due to the absorption of the probe beam exhibited good agreement with the experimental results. Finally, in case of nK/nRb = 4.85, it is estimated that a sensitivity of 1.6 fT/Hz1/2 can be achieved by increasing the temperature to 270 °C.
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Fig. 1: The experimental setup of OPMs. The hybrid cell and three pairs of coils were placed in a three-layered mu-metal magnetic shield.
Fig. 2: The numerical calculation model.
Fig. 3: The temperature dependence of the output signal of OPMs. (a) depicts the experimental results as a function of the temperature of the hybrid cell, and (b) depicts the numerical calculation results plotted against the temperature based on Eqs. (1), (2), (6), and (7).
Fig. 4: (a) depicts the dependence on the probe beam power of transmitted light intensity, and (b) depicts the output signal of OPMs as a function of the probe beam power.
Fig. 5: Measured data of nK/nRb = 4.85 and calculated results considering the relaxation of the absorption of the probe beam plotted against the temperature. The relaxation rate was varied and the calculated result with RPR = 1.5 × 103 s−1 agreed with the measured data.

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