We investigate here both theoretically and experimentally light-induced scattering in (111)-cut ${\mathrm{Bi}}_{12}{\mathrm{TiO}}_{20}$ crystals with an external ac field. Our simple analytic solution, which is nearly as precise as the numeric one, allows us to recognize the following otherwise hidden general features. Without the elasto-optic contribution, the scattering patterns are identical for the same value of $\xi ={\zeta }_0+(2/3)\mathrm{}{\phi }_p,$ where ${\phi }_p$ is the initial polarization angle and ${\zeta }_0$ is the angle of the external field. With the elasto-optic contribution, the scattering patterns for the same $\xi$ are still very similar. For $\xi \ne 0,$ the scattering patterns depend differently on the elasto-optic coefficients $p_{12}$ and $p_{13}$ so that in principle $p_{12}$ and $p_{13}$ can be measured by purely holographic experiments. On the experimental side, we present scattering patterns for $\xi =0\mathrm{}$ and $\pm 30°,$ showing thereby the similarity of the scattering patterns for equal values of $\xi .$ In all cases, we obtain good qualitative agreement of our analytic and numeric calculations with the experimental findings.

• Received 31 July 2000

DOI:https://doi.org/10.1103/PhysRevE.63.016607