INTERFEROMETRIC INVESTIGATION OF THE PHASE-TRANSITION IN TGS CRYSTALS

The temperature dependences of the geometrical thickness and refractiv e indices of tile triglycine sulphate (TGS) crystals have been investi gated in the temperature range 22 to 72 degrees C, including the ferro electric phase transition at 49 degrees C, for three crystallographic directions of propagation and polarization of light. The spontaneous c hanges of the parameters studied in the range 39 to 49 degrees C are c haracterized by critical indices 2 beta in the range 0.87 to 0.95. The difference of the critical indices from unity is explained by a signi ficant temperature dependence of the electrooptic, reversed piezooptic , and electrostriction coefficients of maximum-like character in the r ange of the phase transition.