Abstract
In this paper, the voltage-transmittance curvesKDP crystals were measured accurately between two crossed or parallel polarizers using longitudinal electro-optic effect. The end faces of rectangular KDP samples were coated with ring-shaped electrodes using conductive silver paint (CSP). The change of half period voltage ${U_i}$ has been investigated. A method for quantitative characterization of residual stress has been proposed, based on deviation voltage ${U_d}$. The results demonstrate that loading voltage is close to the integration of electric field intensity in crystal along the optical path when the CSP ring electrodes have a large outer radius $R$, small inner radius $r$, and long-distance $d$. The half-period voltage ${U_i}$ is also close to longitudinal half-wave voltage ${U_\pi}$ in these circumstances. The unclamped electro-optic coefficient $\gamma^{\sigma}_{63}$ of KDP crystal at room temperature was measured as ${10.24}\;{\pm}\;{0.05}\;{\rm pm/V}$ at the wavelength of 632.8 nm.
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