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The defect structure of TGS single crystals grown at constant temperature above TC, each at different constant supersaturation, is investigated by ultramicroscopy and Lang X‐ray topography. It is found that the defect density decreases with decreasing growth rate even at rates lower then 1 mm/d. The decreasing volume defect and dislocation densities are followed by an increase of maximum permittivity εmax, a decrease of coercive field Ec and a slight increase of the temperature of the phase transition TC. The effect is interpreted as a consequence of decreasing inhomogeneity of the crystals caused by reducing the number of defects, and its physical mechanisms are discussed. Further, the conditions for obtaining TGS crystals in which high‐quality regions exist, are analysed.

A novel method of measuring the refractive-index profile of deep multimode planar waveguides is described. Unlike in mode spectroscopy, several modes are excited simultaneously by a prism coupler. Superposition of the modes forms a guided beam that refracts continuously inside the graded-index waveguide and reflects periodically from the waveguide surface. Measurement of the periodicity as a function of the excitation angle enables one to calculate the refractive-index profile of the waveguide.

From the study of pyroelectric coefficient p* during constant-rate-temperature-increase (0,03-1,5 °C.s-1) its thickness dependence was found (for the thickness decrease from 3 mm to 0,4 mm p* decreases eight times) and explained by the influence of ferroelectrically inactive surface layers. The effect is to be expected at any measuring method