Electro-optical properties of Sn2P2S6

The electro-optical (EO) properties of monoclinic Sn2P2S6 single crystals are measured by direct interferometric technique for electric fields applied parallel to the crystallographic x-axis that lies near the spontaneous polarization vector. The room temperature free EO coefficient r(111)(T) reaches 174 +/- 10 pm/V at lambda = 633 nm and shows only weak dispersion in the wavelength range between lambda approximate to 0.6,...,1.3 mum. Corresponding values of r(221)(T) and r(331)(T) at lambda = 633 nm are 92 8 and 140 18 pm/V, respectively. The temperature dependence of the EO coefficients near the structural phase transition at T-C = 65 degreesC is well described by a Curie-Weiss law with a peak value r(111)(T) congruent to 4500 pm/V. The ratio between the free and clamped EO coefficients is determined at the wavelength lambda = 633 nm by applying a fast pulsed electric field instead of an AC field and measuring the temporal evolution of the electrically induced refractive index change. The values are r(111)(S)/r(111)(T) = 0.30 +/- 0.02, r(221)(S) /r(221)(T) = 0.12 +/- 0.02 and r(331)(S) /r(331)(T) = 0.30 +/- 0.09. (C) 2002 Elsevier Science B.V. All rights reserved.