The Kerr effect in KCl and the role of impurities

The Kerr constants (R1111-R1122) and R1212 of KCl containing Cd2+ ions in the concentration range from 10 -2 to 10-1 mol.% and KCl containing 10-1 mol.% of Br- ions, KCl0.8Br0.2 and KCl 0.4Br0.6 have been determined. In KCl:Cd2+ the state of the Cd2+ ions has been investigated using the ionic thermoconductivity (ITC) technique and the volume change brought about by these impurities has been studied using powder, X-ray diffractograms. The processes by which the kerr effect is produced in alkali halides containing different classes of defects have been discussed. The authors conclude that the observed Kerr effect is due to (i) the polarisability anisotropy of the ions (chiefly of impurities) and (ii) the electrostrictive elasto-optic effect which coexist in a crystal when a high electric field is applied. The relative importance of the two processes mentioned above, in alkali halides containing different classes of defects, has also been discussed.