Piezo-optic birefringence in NaCl structure crystals. II. Applications

Abstract

The theory outlined in Part I is shown %o yield the correct values of the strain-optical coefficients Pn and P~e, the sign reversal of (Pn-Pn), and ionic polarizabilities. In the light of the theory, the following effects have also been examined. (i) The effect of elastic deformation on oscillator strengths and the frequencies of optical electrons, (ii) effect of temperature on ionic polarizability, and (iii) the temperature and wavelength dependence of the strain-polarizability constant under hydrostatic pressure.

An empirical model of optical susceptibilities of crystals II. Elasto-optical effect in alkali halides

“…Distinguishing between both kinds of deformation we obtain: (Meseguer and Sanchez, 1978) for photon energies between 2eV and 6eV show that the dispersion of />44 above 600 nm can be neglected. Measurements in the visible region (Bansigir and Iyengar, 1961) indicate that for NaCl, KCl, KBr, and KI, pu and p12 increase with increasing wavelengths. However, the dispersion of the same coefficients in these compounds determined near the ultraviolet spectral region (Rahman and Iyengar, 1970) suggests that all elasto-optic quantities become independent of wavelength in the near infrared region.…”

Effect of wavelength on the sign of the photoelastic constant (P11–P12) of crystals of sodium-chloride structure

“…1 Pat and P~ 2 are the strain-optical constants, n the refractive index, a Poisson's ratio, ,6 the number of valence electrons, /'1, f2 the oscillator strengths, 0 = ctj/r 3 (cq is the polarizability of the jth ion and r is the interionic distance) and 20 is the strain polarizability constant. Using these expressions, Bansigir & Iyengar (1961b) calculated the wavelengths at which the photo-elastic constant (P~I-P~2) changes sign for KC1, KBr and KI crystals. The method adopted is based on an empirical relation that ~j/~ varies linearly with 1/).2 in the visible region (ct is the sum of the polarizabilities of the two types of ion and 2 is the wavelength of light).…”

“…It is observed (Rahman & Iyengar 1966;Bansigir & Iyengar, 1961b) that the variation of the photo-elastic constant P12 is less than 5 % for the entire wavelength range (from ultraviolet to the visible region). In view of this observation, one can evaluate the value of Px2 approximately in the ultraviolet region from the observed value of P12 in the visible region.…”