The quadratic electro‐optical (Kerr) effect in alkali halides increases by several orders of magnitude when substitutional impurities, which give rise to dipole defects alignable by an external electric field, are added to them. The Kerr constants (R1111 – R1122) and R1212 of KCl containing Cd2+ and Sr2+ as impurities are determined for different concentrations of the dopants. The constants are found to be of the order of 10−17 m2 V−2, which is about five orders of magnitude greater than those of pure KCl. Copyright © 1988 WILEY‐VCH Verlag GmbH &amp; Co. KGaA

Nirmal Kumar Ramesh

Electrooptical effects

Dielectric constant

KERR EFFECT

ALKALI METAL COMPOUNDS

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physica status solidi (a)

The quadratic electrostrictive coefficients of KCl containing substitutional impurities (KCl:Br−, KCl0.8Br0.2, KCl0.4Br0.6, KCl:Tl+, KCl:Cd2+, and KCl:Mn2+) are determined from the stress dependence of static dielectric constants. Small changes in the capacitance of the samples under the application of uniaxial stress are measured with the aid of a bridge circuit and a lock‐in amplifier. The values of the components of the electrostriction tensor of the doped systems are found to be enhanced by one to two orders of magnitude compared to those of the pure KCl crystal. The increment of the electrostrictive coefficients of KCl on doping is attributed to (i) the phenomenological description of a point defect as an anisotropic elastic dipole and the orientation of such defects; (ii) an additional deformation of the lattice arising from the reorientation of the I–V dipoles in the case of KCl containing divalent impurities. Copyright © 1992 WILEY‐VCH Verlag GmbH &amp; Co. KGaA

physica status solidi (b)

Determination of the Quadratic Electrostrictive Coefficients of Some Doped KCl Crystals

The strain-optic contribution to the electro-optic effect in KCl doped with Br-, Tl+, Cd2+ and Mn2+ ions has been evaluated from the independent measurements of the photoelastic and the electrostrictive coefficients and the true electro-optic coefficients have been calculated. The relatively small electrostrictive elasto-optic contribution in these doped KCl systems has been discussed in the light of the change in the ionicity of the bonds between the impurity ions and the Cl- ions. The possible application of the systems KCl:Cd2+ and KCl:Mn2+ at high (microwave) frequencies has been discussed in comparison with KTaO 3.

Journal of Physics: Condensed Matter

Evaluation of the true electro-optic effect in some doped KCl crystals

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.

The Kerr effect in KCl and the role of impurities

The wavelength dependence of the Kerr constants (R1111 — R1122) and R1212 in KCl: Cd2+ and KCl: Sr2+ is found in the range 290 to 650 nm at room temperature. The studies are carried out for crystals containing different concentrations of substitutional impurities, Cd2+ and Sr2+. The experimental results are fitted to a simple Sellmeier type relation and the dispersion constants are studied. Copyright © 1989 WILEY‐VCH Verlag GmbH &amp; Co. KGaA

Dispersion of the Quadratic Electro‐Optical (Kerr) Constants in KCl: Cd2+ and KCl: Sr2+

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Books and Monographs Received Through December 1987

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.

Journal	physica status solidi (a)
ISSN	00318965
Open Access	No