On Isotropic Points in K 2 SO 4 Impurity Crystals

The temperature, spectral and baric dependences of birefringence Δni of potassium sulfate crystals doped with 1.7% of copper are studied. It is established that the impurity introduction changes an absolute value of Δni and leads to an increase of the temperature dependence Δnі(Т). It is shown that the isotropic points, which are shifted towards low temperatures by 5 and 11 K, respectively, compared to a pure crystal, appear in a doped potassium sulfate crystal. It is established that uniaxial stresses change the magnitude of absolute values of Δni, as well as the domain of existence of the isotropic state. The generalized temperature–spectral–baric diagrams of the isotropic state of a doped potassium sulfate crystal are plotted, which make it possible to use them as a crystallooptic sensor.