Dispersion in the Linear and Second‐Order Bond Polarizabilities of Alkali Halides

Abstract

An analysis of dispersion in the linear bond polarizability and in the lattice contribution to the second-order polarizability of some alkali halides is performed. The linear and nonlinear polarizabilities are evaluated employing the elasto-optic coefficients p1 p 1 2 , and pd4. The results obtained show significant wavelength dependence of the linear polarizability and the longitudinal component of the second-order polarizability. The anisotropy of the bond polarizability is also found to be frequency dependent.

Calculations of Nonlinear Refractive Index of Alkali Halides

“…The long-wavelength values n 1 of the linear refractive index which are shown in Table 1 were taken from Lowndes and Martin (1969) and Lines (1990). According to the results presented in Kucharczyk (1994b), changes of b L and b T with the light frequency are noticeable on approaching the interband absorption edge in the ultraviolet region. Therefore, we neglected in our calculations the dispersion of b L and b T when extrapolating their values to the long-wavelength limit.…”

“…Such an absolute scale based on measurements in crystalline quartz is recommended in Landolt-Bo¨rnstein Tables (1984). Following the discussion presented previously (Go´rski et al 1996(Go´rski et al , 1997Kucharczyk 1995), in our work we adopted this recommended scale which is roughly midway between the lowest (Adair et al 1989) and the highest (Smith et al 1975) proposed scales and is also close to two other sets of absolute values derived from calibrations based on Raman scattering crosssections (Marker and Terchune 1965;Lynch et al 1974).…”

“…Equation (15) has been proposed for moderately ionic compounds and its failure, when applied to highly ionic crystals, can be discussed in terms of the non-applicability of the harmonic oscillator approximation in describing the motion of q eff in these compounds (Levine 1973a;Kucharczyk 1995). A different way of obtaining the effective bond charge of LiF, NaF, NaCl, NaBr, KF, KCl and KBr, as derived from experimental third-order nonlinear optical susceptibility, has been presented in (Kucharczyk 1995), where q eff has been found to be closely related with the Szigeti effective charge and the Phillips-Van Vechten ionicity f i . The correlations have been next extended to other alkali halides, thus allowing us to estimate q eff for those crystals for which the third-order optical susceptibility has not been measured yet (Kucharczyk et al 2000).…”

“…In terms of the approach the nonlinear refractive index of the rock saltstructure crystals can be expressed as (Kucharczyk 1995) …”