Nanocomposites and nanomaterials 

Nonlinear optical effect in hybrid liquid crystal cells made with natural opal
Bugaychuk S.A.1, Negriyko A.M.1, Gnatovskiy O.V.1, Tarakhan L.N.1, Medvid N.V.2
1 Physics of Crystals Department, Institute of Physics of the NAS of Ukraine. Prospect Nauki, 46, Kyiv-03039, Ukraine. 
E-mail: bugaich@iop.kiev.ua
2 NationalUniversity of Food Technology. Vladimirskaya str. 68, Kyiv-01033, Ukraine.

Nonlinear optical properties in hybrid liquid crystal (LC) cells firstly have been investigated by our group [1]. The cell consists of two different materials separated by a layer of a nematic LC. One material was a glass with ITO electrode, and the second one was a silicon crystal with a periodic microstructured surface. The nonlinear optical mechanism was connected with reorientation of the LC molecules inside a bulk of the cell, which had been enhanced by an initial reorientation of the molecules on the microstructured surface. In these cells a strong nonlinear optical response had been combined with high-order spatial multiplexing that was defined also by the microstructured surface.
In the present work we have prepared and investigated new hybrid cells, which are based on a natural opal. Opal has well-ordered structure of spheres of a size 150-300 nm and consist of SiO2 molecules. The nonlinear optical properties have been investigated by applying the dynamic holographic technique with two-wave mixing, based on continuous Nd:YAG laser operating on the second harmonic at =532 nm. We have studied influence of the nanostructured surface on the optically induced reorientation of the molecules, and by this way on the phase modulation. The mechanism of enhancement of the optical nonlinearity due to generation and control of defects on the nanostructured surface is proposed and discussed.
Hybrid LC cells exhibit strong nonlinear optical properties and are considered as perspective elements for the purposes of all-optical information processing.  

1.	Bugaychuk S., Iljin A., Lyvynenko O., Tarakhan L., Karachevtseva L. Enhanced nonlinear optical effect in hybrid liquid crystal cells based on photonic crystal  // Nanoscale Research Letters.-2017.-11:449.-P. 1-9.