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The results of investigations the elastic and photoelastic properties of a number of garnets crystals obtained by Mandelshtam‐Brillouin technique including the data of ultrasonic experiments are represented. The velocity of sound propagation, the character of elastic interaction between ions in the lattice, nature of photon–phonon interaction in garnets is revealed. The mechanical, thermal and acoustooptical properties of garnets are rated using measured elastic and photoelastic data. The obtained results allow to predict a number of important characteristics of crystals with garnet structure and promote the development of materials with given properties.

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A significant increase of the divergence and appearance of a fringe system has been observed by illuminating of MBBA (p-n-methoxybenzilidene-p-butylaniline) and OCB (octyl-cyano-biphenyl) nematic liquid crystalline samples with a collimated beam of an argon ion laser. The dependence of this effect on laser power. beam polarization, and angle of incidence has been studied in homeopolar and planar sandwich-like cells of 50-150 pm thickness, in the nematic phase. At a homeopolar cell of MBBA (150 pm thickness), at normal incidence a threshold laser power of 45 mW was found. The phenomena can be explained as deformation of the orientation by the Fredericks effect due to light fields. The observations are in good agreement with the theoretical predictions including an estimation of the laser power threshold.

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