Interferometric Investigation of the Phase Transition in TGS Crystals

Abstract

The temperature dependences of the geometrical thickness and refractive indices of the triglycine sulphate (TGS) crystals have been investigated in the temperature range 22 to 72 °C, including the ferroelectric phase transition at 49 °C, for three crystallographic directions of propagation and polarization of light. The spontaneous changes of the parameters studied in the range 39 to 49 °C are characterized by critical indices 2β in the range 0.87 to 0.95. The difference of the critical indices from unity is explained by a significant temperature dependence of the electrooptic, reversed piezooptic, and electrostriction coefficients of maximum-like character in the range of the phase transition.