We describe an interferometric technique suitable for determination of piezo-optic coefficients (POCs) in crystals. The method considers real nonparallelism of measured samples, thereby improving the measuring precision of POCs significantly. Corresponding equations are derived for the interferometric half-wave stress method. Using this technique we have determined a complete set of POCs of pure and $\mathrm{Mg}\mathrm{O}$-doped $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_3$ crystals. The reliability of the data has been confirmed by comparing the effective POCs expressed through the combinations of measured POCs and the effective POCs determined independently using highly precise optical birefringence measurements. Pure and $\mathrm{Mg}\mathrm{O}$-doped $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_3$ crystals reveal nearly the same magnitudes of POCs. However, $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_3$:MgO exhibits about 4 times higher resistance with respect to powerful light radiation, making it more suitable for application in acousto-optic devices that deal with superpowerful laser radiation.

On the basis of studies of the piezo-optic effect, it has been shown that $\mathrm{Sr}{\mathrm{B}}_4{\mathrm{O}}_7$ crystals can be used as efficient acousto-optic materials in the vacuum ultraviolet spectral range. The full matrices of piezo-optic and photoelastic coefficients have been experimentally obtained for these crystals. The acousto-optic figure of merit and the diffraction efficiency have been estimated for both the visible and deep ultraviolet spectral ranges.

All components of the piezo-optic coefficient matrix of calcium tungstate crystals, belonging to the 4/ m symmetry class, are determined. The reliability of the piezo-optic effect measurements in CaWO