Third column electro-optical coefficients of monoclinic Sn_2P_2S_6

All coefficients of the third-column of the unclamped electro-optic tensor of Sn2P2S6 single crystals are determined by direct interferometric techniques. It is found that the largest coefficient r113T for electric field parallel to the z-axis is ≈ 67 pm/V at the wavelength of 633 nm and room temperature.