Browsing by Author "Yukita, Shunpei"

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Giant Pockels effect of polar organic solvents and water in the electric double layer on a transparent electrode
(2017-01-01)
Kanemaru, Hironori
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Yukita, Shunpei
;
Namiki, Hajime
;
Nosaka, Yugo
;
Kobayashi, Takayoshi
The Pockels effect of polar organic solvents and water within the electric double layer (EDL) on an indium-tin-oxide (ITO) electrode is studied to find that water has the largest Pockels coefficient (230 pm V-1), followed in order by methanol (200 pm V-1), ethanol (84 pm V-1), and dimethyl sulfoxide (DMSO) (20 pm V-1). Electrolyte solutions of water and methanol have nearly the same magnitude of Pockels coefficient, while ethanol and DMSO solutions exhibit two and ten times smaller Pockels coefficients than the methanol solution, respectively. The Pockels coefficient scales well with the hydrogen-bond strength (or average cluster size) divided by the solvent viscosity. This suggests that hydrogen bonding and viscosity play crucial roles in the mechanism of the Pockels effect of these liquids.
Mechanisms of the anomalous Pockels effect in bulk water
(2018-04-01)
Yukita, Shunpei
;
Suzuki, Yuto
;
Shiokawa, Naoyuki
;
Kobayashi, Takayoshi
;
Tokunaga, Eiji
The "anomalous" Pockels effect is a phenomenon that a light beam passing between two electrodes in an aqueous electrolyte solution is deflected by an AC voltage applied between the electrodes: the deflection angle is proportional to the voltage such that the incident beam alternately changes its direction. This phenomenon, the Pockels effect in bulk water, apparently contradicts what is believed in nonlinear optics, i.e., macroscopic inversion symmetry should be broken for the second-order nonlinear optical effect to occur such as the first-order electro-optic effect, i.e., the Pockels effect. To clarify the underlying mechanism, the dependence of the effect on the electrode material is investigated to find that the Pockels coefficient with Pt electrodes is two orders of magnitude smaller than with indium tin oxide (ITO) electrodes. It is experimentally confirmed that the Pockels effect of interfacial water in the electric double layer (EDL) on these electrodes shows an electrode dependence similar to the effect in bulk water while the effects depend on the frequency of the AC voltage such that the interfacial signal decreases with frequency but the bulk signal increases with frequency up to 221 Hz. These experimental results lead to a conclusion that the beam deflection is caused by the refractive index gradient in the bulk water region, which is formed transiently by the Pockels effect of interfacial water in the EDL when an AC electric field is applied. The refractive index gradient is caused by the diffuse layer spreading into the bulk region to work as a breaking factor of inversion symmetry of bulk water due to its charge-biased ionic distribution. This mechanism does not contradict the principle of nonlinear optics.