Marek Izdebski

A new approach to the dynamic polarimetric method is proposed, which allows for the decoupling of electro-optical Kerr effect measurements from the electro-absorption effect in partially transparent liquids. The method is illustrated by using the results of engine oil measurements as a function of temperature and modulating field frequency. It was shown that the birefringence induced in the sample, the modulation of the ordinary wave transmission, and the modulation of the extraordinary wave transmission in the sample can be shifted in phase with respect to the square of the applied alternating modulating field. Each of these three phase shifts can depend differently on the temperature and frequency. Neglecting the influence of electro-absorption on electro-optical measurements in liquids or considering electro-absorption as an effect correlated in phase with induced birefringence may lead to significant measurement errors. This indicates that the Kerr constant and the electro-absorption coefficients for an alternating electric field should be considered as complex quantities instead of real values, as they have been traditionally. The proposed approach fills an important gap in measurement techniques described in the literature, which may provide erroneous results for measurements of the Kerr constant in partially transparent liquids including many industrially important liquids.

The electro-optical properties of methyl silicone oils with viscosities ranging from 10 to 10,000 cSt have been studied extensively to verify their suitability as immersion liquids. Immersion liquids are often used in nonlinear optics to protect hygroscopic crystals from moisture, reduce multiple reflections, and protect against electrical breakdown. However, the lack of experimental data makes it difficult to select an optimal liquid that does not exhibit a significant electro-optical Kerr effect in the fringing electric field around the electrodes on the crystal. Electro-optical measurements were performed using an improved dynamic polarimetric method, which compensates for the measurement errors caused by inaccurate positioning of the electro-optical modulator’s operating point on its transmission characteristics. The values of the Kerr coefficient ranged from −8.83 × 10⁻¹⁶ to −6.79 × 10⁻¹⁶ m V⁻² for all oil samples, at temperatures from 25 to 80 °C and frequencies from 67 to 1017 Hz. These exceptionally low values, together with a low dielectric constant, very good transparency, and high chemical stability, make methyl silicone oils highly suitable as immersion liquids. The Kerr coefficient and other electro-optical coefficients increased with increasing temperature. This unusual result cannot be adequately explained by Buckingham’s molecular theory of the Kerr effect.

The application of the improved dynamic polarimetric method for the measurement of the quadratic electro-optic effect in NH₄H₂PO₄ (ADP) crystal with the light beam propagating perpendicularly to its optical axis is presented. This technique can be applied in noncetrosymmetric crystals in the presence of natural birefringence even when the fast and slow rays diverge slightly, causing them to only partially interfere. The method allows for minor errors in cutting and orientation of the crystal samples, resulting in deviations from configurations in which the crystal symmetry vetoes the linear electro-optic effect. The occurring contribution of the linear effect, if it is not too large, not only does not exclude the measurement of the quadratic effect, but increases its accuracy. The method does not require any prior compensation for the natural birefringence. Its sensitivity allows for quadratic electro-optic effect measurements in ferroelectrics in temperatures significantly different from the phase transition temperature or in paraelectric crystals, for which this effect is relatively small.

In this paper, a method of measuring the β₃₁ coefficient of the quadratic electrogyration effect in potassium dihydrogen phosphate (KDP)-type crystals is proposed. It is shown that this very weak effect can be decoupled from other stronger effects occurring simultaneously in the real measuring system, even when small inaccuracies in crystal cutting and alignment are taken into account. Theoretical and numerical analyses are illustrated by experimental data obtained for the KDP crystal. High sensitivity, which is required for successful measurements at room and higher temperatures, has been achieved by using the polarimetric method for a light beam propagating along the optical axis of the crystal in combination with the lock-in technique and a new measurement procedure that compensates for the contribution of other effects such as electro-optic effects, natural birefringence and dichroism. It was found that the β₃₁ coefficient measured at a wavelength of 632.8 nm decreases linearly from 2.53 × 10⁻²¹ m² V⁻² at a temperature of 298 K to 2.08 × 10⁻²¹ m² V⁻² at 343 K.

A new single‐layer kinetic block model of crystal growth is proposed, which takes into account preference for bonds between blocks of the same type over mixed‐type bonds. The obtained parameters describing stable growth conditions were compared with other theoretical models (such as thermodynamic Jackson model and the earlier proposed kinetic model based on zeroth order approximation) which assume that new growth units are attached in a completely random way. Additionally, the results were compared with Monte Carlo simulations. The proposed model produced results which matched the simulation results much better than the other theoretical models. The new model can be used for studying crystal growth both from solution and from vapour. Calculations based on this model show that the number of created mixed‐type bonds depends on the temperature and is lower from its estimation obtained with the use of the zeroth order (Bragg‐Williams) approximation.