On Isotropic Points in K2SO4 Impurity Crystals

The temperature, spectral and baric dependences of birefringence Δ n i of potassium sulfate crystals doped with 1.7% of copper are studied. It is established that the impurity introduction changes an absolute value of Δ n i and leads to an increase of the temperature dependence Δ n і ( 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 Δ n i , 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.