Strain-Optical Constant (p44) of Mixed Crystals of KCl-KBr of Equimolar Concentration

Abstract

Recently, Kumar et al. had determined the piezo-optic constants of mixed crystals of KCl-KBr /1/ and KBr-KI /2/. A theory of piezo-optic birefringence characterised by strain-optical constants (pll -q2) for mixed crystals of equimolar concentration of NaCl structure was developed by Kumar et al. /3/. This theory is now extended to the study of birefringence characterised by the constant p44 for mixed crystals of KC1-KBr of equimolar concentration and is valid for any mixed crystal having the same structure and composition.A crystal with its edges parallel t o DlO], .[OOl], and [11@ (to be called XI, y', and z', respectively) is stressed along ZI and observation is made along y' .The strain-optical constant p44 and induced refractive index changes are related to strain d through the following expression based on Pockel's theory /4/:where n is the refractive index in the unstrained condition, nxl and nzl are the altered refractive indices for light vibrating in x' and ZI directions.Attributing the changes in refractive indices to i ) change in density of the crystal, ii) Lorentz-Lorenz anisotropy due t o material continuum, iii) Lorentz-Lorenz anisotropy due t o dipoles within the assumed cavity, iv) Coulomb anisotropy due t o charges within the cavity, and following the same procedure as Kumar et al. /3/, an expression for the birefringence'was developed and is given by 1 ) Hyderabad 500 007, India.