Elasto-Optic Anomaly in KH2PO4

A Curie-Weiss anomaly in the elasto-optic (Pockels') coefficient ${p_{66}}^{E=0\mathrm{}}$ measured under the "shorted" condition has been observed by spontaneous Brillouin light scattering above the ferroelectric transition at 122°K. The observed relation ${p_{66}}^{E=0\mathrm{}}=-0.0345-\frac{2.132}{\mathrm{}(T-117.45\mathrm{})\mathrm{}}$ is shown to be a direct consequence of the anomaly in the "clamped" dielectric constant ${{\epsilon }_{33}}^{X=0\mathrm{}}$.