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Reference: ISH2015_494

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Measurements of Poisson's field using electo-optic Kerr effect



In this paper, to quantitatively examine the measurement capability of Poisson's field using electro-optic Kerr-effect (EOKE), Kerr constants of neutral molecules and ions were examined. Kerr constants are determined by dipole moment, polarizability, and hyperpolarizability of molecules. Since these values are fundamentally quantum mechanical, computations was done by means of first principle quantum chemistry methods. The computed Kerr constants for neutral molecules (N2, CO2, SF6 and CF3I) were within 50% error of the experimental values, comparable to the scattering between experimental values itself. The results showed that SF6 has smaller Kerr constants compared to those of N2 and CO2 due to its high molecular symmetry. In contrast, CF3I has higher Kerr constant due to its permanent dipole. The computed Kerr constants for anions were larger by two orders of magnitude than those of neutral molecules. The difference is probably due to the shielding effect; electrons of anions are less attracted to the nucleus and likely to polarize under external electric field. For cations, the opposite holds true. However Kerr constants contain the anisotropic polarizability term, which is strongly influenced by the anisotropy of electron density distribution, and thus can be larger for cations. As a result, the calculated Kerr constants of cations were comparable to or smaller than those of neutral molecules. The ratio of Kerr constants of ions to those of neutral molecules did not exceed 103. Thus it was shown that EOKE is valid for measuring electric field in weakly ionized gas whose ionization degree is smaller than 10-3. Finally we measured the temporal response of electric field between a wire electrode and plane electrode at the presence of corona discharge in air at atmospheric pressure.

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Year: 2015

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