This paper presents the results of ultrasonic measurements of ${\text{LiNbO}}_3$ and ${\text{LiNbO}}_3:\text{MgO}$ crystals. The tensors of piezoelectric coefficients, elastic stiffness constants, and elastic compliances are determined for both crystals at room temperature. Combining these data with the results of piezo-optical measurements, a complete set of photoelastic tensor coefficients is also calculated. Doping of ${\text{LiNbO}}_3$ crystals by MgO does not lead to a considerable modification of their elastic and photoelastic properties. However, ${\text{LiNbO}}_3:\text{MgO}$ is characterized by a considerably higher resistance with respect to powerful light radiation, making it promising for future application in acousto-optic devices that deal with superpowerful laser radiation. Presented here are the complete tensor sets of elastic constants and photoelastic coefficients of ${\text{LiNbO}}_3$ and ${\text{LiNbO}}_3:\text{MgO}$ crystals that may be used for a geometry optimization of acousto-optical interaction providing the best diffraction efficiency of acousto-optical cells made of these materials.

Paper reports the second harmonic generation (SHG) in ferroelectric $\text{AgNa}{\left({\text{NO}}_2\right)}_2$ crystals being driven by the spontaneous and electric field induced polarizations. Obtained results are interpreted within the phenomenological theory which considers the free energy describing the interaction between the spontaneous or electric field induced polarizations and spatially inhomogeneous electric polarizations resulted from propagating optical waves. Relatively high magnitudes of the effective second order nonlinear optical (NLO) susceptibilities in these crystals are combined with several phase matching geometries which allows to consider them as high-performance materials for potential NLO applications, such as parametric generation and amplification, frequency doubling, or other applications that require high-efficient frequency conversion. In addition, an anomalously large response of NLO susceptibilities with respect to an applied electric field has been found in the vicinity of the Curie point. This may also have a number of applications, especially in those devices where an efficient tunable control of SHG intensity is demanded.

We suggest a method for optimizing geometry of acousto-optic (AO) interactions in anisotropic crystalline materials. Within the framework of this method, one gets global maximums of AO figure of merit M₂ and their spatial orientations, proceeding from so-called “extreme” indicative surfaces, which are obtained after finding such an acoustic wave propagation direction that maximizes the M₂ parameter for each propagation direction of the incident electromagnetic wave. The method improves earlier indicative surface-based techniques in several aspects, particularly in properly accounting for the momentum conservation condition for the AO diffraction, and yields a higher accuracy in assessing spatial anisotropy of the AO effect. We have constructed the extreme surfaces of LiNbO₃ crystals for all possible cases, including those of isotropic/anisotropic AO diffractions and longitudinal/transverse acoustic waves. The anisotropy of the AO figure of merit for LiNbO₃ is analyzed for the acoustic frequencies 0.01–2.0 GHz and the light wavelengths 405–1444 nm. The absolute M₂ maximums refer to ‘indirect crystal cuts' and are equal to 26.3 × 10⁻¹⁵ s³/kg at 2 GHz and 405 nm, and 15.4 × 10⁻¹⁵ s³/kg at 0.4 GHz and 1444 nm.

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.

We report the spatial anisotropy of the acousto-optic (AO) figure of merit $M_2$ in ${\text{LiNbO}}_3$ crystals. The analysis is based on the indicative surfaces being calculated for several geometries of the AO diffraction. Basing on these results the most efficient geometries of AO cells made of ${\text{LiNbO}}_3$ crystals are determined. It is revealed that the cells made of certain nondirect crystal cuts provide several times better AO diffraction efficiency comparing to the traditional ones, i.e., made of direct cuts of ${\text{LiNbO}}_3$ . The obtained results present considerable practical interest since may be useful in a designing of highly efficient AO cells made of ${\text{LiNbO}}_3$ crystals. The methodology developed in the present work may be applied to other crystal materials as well.