Kerr effect in KCl:Pb²⁺ and KCl:Cu⁺

Pure ionic cubic crystals like alkali halides exhibit a very small birefringence under the influence of an external electric field. The effect, however, increases by several orders of magnitude when substitutional impurities, which give rise to dipole defects alignable by an electric field, are added to the crystal. The quadratic electro-optic constants (Kerr constants) R1212 and (R1111-R1122) of KCl containing Pb2+ and Cu+ as impurities have been determined for different concentrations of the impurities. A static compensator method has been used for the measurements. The constants are found to be of the order of 10-14 cm2 V-2, which is about four orders greater than those for pure KCl.