Nanocomposites and nanomaterials

Nonlinear optical dynamic systems based on nematic liquid crystals with gold island films
A. Gridyakina1, H. Bordyuh1, S. Bugaychuk2, L. Viduta2, V. Styopkin2, A. Polishchuk1
1 National Aviation University, Liubomyra Huzara avenu 1, Kyiv 03058, Ukraine.
E-mail: gridyakina@nau.edu.ua
2 Institute of Physics of the NAS of Ukraine, Nauki avenu 46, Kyiv 03028, Ukraine

Nowadays there is a great need in development of holographic methods for transmitting, processing and converting optical information, which are useful in various fields including communication technologies, space research, biological studies, and medicine. The main elements of such systems are spatial light modulators (SLM), which are created on the basis of liquid crystals (LC). Under the action of applied voltage LCs change their linear and nonlinear optical properties through the mechanism involving reorientation of LC molecules. However, response time of reorientation of the molecules to an electric signal is quite large, usually it is more than 100 ms for nematic LCs. So, it is important to create LC systems with ultra-fast response time.
In our work gold nano-island film was deposited onto ITO electrode of one of the substrate of a cell. It was experimentally shown that use of gold island films of different morphology causes a nonequilibrium dynamics of charge redistribution on the surface under the combined action of laser radiation and voltage. The mobile charge redistribution accelerates the reorientation of LC molecules since there is no strong anchoring of LC molecules to the surface.
Using the abovementioned conditions, for the first time we revealed a fast nonlinear optical effect in the composite LC cells based on E7 nematic mixture. With these cells we observed the generation of many diffraction orders and the efficient energy transfer, which depended on the applied voltage. Also, the cells exhibited fast response time. Using such cells we obtained the frequency mode for switching on/off by applying alternating voltage. Decrease in the time of reorientation of LC molecules can be explained by surface-induced photorefractive effect at the inorganic-organic interface, consisting of ITO electrode coated with gold nano-island film and organic LC molecules distributed over this inhomogeneous conductive surface.

1. S. Bugaychuk, L. Viduta, A. Gridyakina, H. Bordyuh, et al., Faster nonlinear optical response in hybrid liquid crystal cells containing gold island films, Appl. Nanosci (2020). https://doi.org/10.1007/s13204-020-01384-0.