Optical second-harmonic generation (SHG) is used as a noninvasive probe of two-dimensional (2D) ferroelectricity in Langmuir-Blodgett (LB) films of the copolymer vinylidene fluoride with trifluoroethylene. The surface 2D ferroelectric-paraelectric phase transition in the topmost layer of the LB films and a thickness-independent (almost 2D) transition in the bulk of these films are observed in temperature studies of SHG.

Articles you may be interested inStructural and dielectric properties of laser ablated BaTiO3 films deposited over electrophoretically dispersed CoFe2O4 grains A comprehensive investigation on the phase transformation behavior and electrical properties of ( Pb 1 − x Ba x ) ZrO 3 ( 0 ≤ x ≤ 0.5 ) thin films Ferroelectric phase transitions and the structure of KNbO 3 nanometer-thick films deposited by Metal-organic chemical-vapor deposition technique on a MgO͑100͒ substrate are studied. Thin KNbO 3 films of the average thickness from 20 to 150 nm possess a grainlike structure with a lateral grain size of about 250 nm. Such films reveal ferroelectric properties similar to KNbO 3 single crystal. Temperature dependencies of optical second harmonic generation intensity show that the Curie temperature T C of the nanometer-thick KNbO 3 films is about 30°C lower than the T C of KNbO 3 single crystal, which is attributed to size effects in KNbO 3 nanograins.

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The interest in hyperbolic metamaterials is fueled by fascinating optical properties exhibited by this class of artificial media. Their optical features originate from hyperbolic dispersion emerging due to the shape anisotropy of the metal–dielectric composite. In this work, we study experimentally and numerically the second-harmonic generation (SHG) in ordered arrays of Au nanorods embedded in porous aluminum oxide. Strong increase of the SHG intensity in the vicinity of the epsilon-near-zero (ENZ) spectral point accompanied by dramatic phase modulation of the SHG wave is revealed. These effects are attributed to resonant enhancement of the electric field of the light wave and transition from the elliptical to hyperbolic dispersion law in hyperbolic metamaterials near the ENZ point.

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Ferroelectric ordering, the electroclinic effect and chiral smectic C (SmC*) -smectic A (SmA*) phase transitions in thin planar ferroelectric liquid crystal (FLC) cells are studied by means of linear electrooptic and second harmonic generation techniques. The ferroelectric switching is detected in biased FLC cells by measuring azimuthal dependences of linear and nonlinear responses. The applied DC-electric field rotates the FLC symmetry axis with initial and final orientations in the cell plane. Comparative studies of the switching behavior in reflection and transmission allows to distinguish the contributions from the bulk and the sub-surface layers of the cell. The analysis of temperature dependence shows the existence of a strong surface coupling. The temperature dependent nonlinear polarization shows a critical behavior corresponding to the superfluid model.

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