Perturbed polariton spectra in optically damaged LiNbO₃

We have performed experimental measurements and quantitative analyses of the influence of optical damage in LiNbO3 upon the polariton spectra. The results show that the principal spectral effect of optical damage is equivalent to a static electric field perpendicular to the crystallographic C3 axis. At T = 100K optical damage levels of 5 KW-hr/cm2 are equivalent to static electric fields of 40 KV/cm applied in the crystallographic y-direction. The analysis provided includes only a single parameter and accounts for the frequencies and intensities of the “forbidden” spectral lines [E(TO) and E(LO) appearing in geometries for which only A1(TO) are permitted.] This agrees with the conclusion of Chen [J. Applied Phys. 40, 3389 (1969)] that charge diffusion is primarily perpendicular to the polar axis, not along it. These electric fields and charge displacements perpendicular to c are presumably metastable.