Crystal optical properties of anisotropic optical materials of which the dielectric tensor is spatially modulated with a sinusoidal wave form are studied in the framework of the Jones calculus. Propagation of polarized light along the directions parallel to and far from the optical axes is considered. Polarization of the normal waves of the medium and the Jones matrix of a finite modulated crystal are derived, enabling us to ascertain the parameters of the apparent macroscopic optical activity. The developed model should describe the optical effects in a planewave region of incommensurate phases with the average inversion symmetry, occurring in the A 2 BX 4 family crystals. The boundary conditions for the phase of the modulation wave, which play a key role in crystal optics of incommensurate phases, are discussed. The model predicts a relatively small optical activity in the birefringent crystal sections and negligible or zero effect in the optical axis directions. The conclusions agree well, at least, with the non-contradictory experimental results on optical rotatory power of the A 2 BX 4 crystals. A comparison with the results derived earlier for the square modulation wave proves that the main conclusions of the model do not depend on the exact modulation shape.

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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.

Abstract. We report on the growth and initial thermal and optical characterisation of a single-crystalline ternary halide, Tl 4 CdI 6 . The crystal is described by the centrosymmetric tetragonal class P4/mnc at the room temperature. The parameters of linear thermal expansion are studied in the temperature region 330-500 K. The crystal is optically positive and reveals very high optical anisotropy (the birefringence ~ 0.13 at 633 nm). Its optical pseudo-gap value corresponds to widegap semiconductors. A broad maximum at 400-410 K found in the temperature dependence of IR radiation-induced second harmonic generation may be indication of a polymorphic phase transformation.

On the basis of the superposition principle for the optical anisotropy parameters and the Jones calculus methods a phenomenological model is developed to interpret the optical properties of absorbing, spatially modulated dielectric materials. The character of the normal electromagnetic waves propagated in a uniaxial, weakly dichroic crystal for which the complex gyration tensor is modulated with the simple square wave form is ascertained. The structure with a perfect modulation wave and the unipolar structure are considered and should describe the multidomain ferroelectric and incommensurately modulated phases. Specific crystal optical effects are found which have no analogues in uniform materials. Proceeding from the normal wave polarization the modulated crystal is shown to be equivalent to a low-symmetry biaxial crystal. The origin of a non-zero eigenwave ellipticity is discussed in connection with the problem of optical activity in macroscopically centrosymmetric incommensurate crystals of A 2 BX 4 group.

The optical activity, birefringence and the indicatrix rotation of a (001) sample of (N(CH3)4)2ZnCl4 are measured in the high-temperature, incommensurate and partly lock-in phases with a new high-accuracy null polarimeter. The optical properties are shown to be sensitive to the annealing and X-irradiation of a sample via the defect concentration changes. The results can be explained by consideration of a modulated gyration tensor in the incommensurate phase, using the idea of modulation wave distortions imposed by defects.

Abstract. In this work we have grown single crystals K x (NH 4 ) 2-x SO 4 (x  1.75), which belong to a potassium-ammonium sulfate family, and studied their roomtemperature structure. Spectral dependences of the principal refractive indices and principal optical birefringences are measured in the visible region. Anomalous birefringence dispersion is observed along the light propagation direction parallel to the principal x axis. According to our birefringence extrapolation based on the Sellmeier fit for the refractive indices, the symmetry of optical indicatrix at the room temperature should increase at the light wavelength λ IP  1350±60 nm. This corresponds to a specific 'isotropic point' defined by the condition n x (λ IP ) = n y (λ IP ), which has not been detected in either K 2 SO 4 or (NH 4 ) 2 SO 4 crystals.

Peculiarities of the non-local responses of spatially inhomogeneous insulating media to electromagnetic waves are considered within a phenomenological approach. In the case of a weak spatial dispersion (SD), a ‘quasi-local’ constitutive equation is derived, which allows one to isolate the effects of SD in relation to non-uniformities of the wavefield and the material properties of the medium. The symmetry of the material tensors is clarified. The material contribution to the SD suggests a novel mechanism for optical activity. The SD in crystalline media is described in terms of dielectric permittivity dependent upon a single argument which is a specific combination of the light wavevector and the reciprocal lattice vectors. The conditions and materials for which the relevant effects can be notable are pointed out. The character of the normal light wave polarization in dielectric crystals of the A2BX4 group with incommensurately modulated superstructure is analysed and the effective crystal optical parameters are derived. It is shown that the first-order material SD effects associated with the bulk macroscopic properties of these crystals could be of practical importance.