Light Scattering from Polaritons in Centrosymmetric Crystals

Polaritons in centrosymmetric crystals (SrTi${\mathrm{O}}_3$ and KTa${\mathrm{O}}_3$) have been studied by small-angle light scattering induced by external electric fields. Measurements of polariton dispersion curves in SrTi${\mathrm{O}}_3$ have produced new values for oscillator strengths of the infrared-active phonons. Absence of a measurable $k$ dependence for the linewidth of the "ferroelectric" mode bears on the discrepancy between Raman and infrared linewidth measurements previously reported.