Nonlinear optical response enhanced by a gold island film in hybrid liquid crystal cells

Dr. Svitlana Bugaychuk (Ukraine)

Video was recorded during the 7th International research and practice Conference "Nanotechnolgy and Nanomaterials" (NANO-2019)

Liquid crystal (LC) valves are intensively investigated as new efficient electrically controlled elements for optical signal processing and laser pulse manipulation [1, 2]. The strong nonlinear optical response in LC cells is associated with the reorientation of LC molecules in the cell volume. Alternatively, the photorefractive mechanism is initiated by the charge distribution on a cell substrate when an electric field is applied. In LC cells with the homeotropic orientation of molecules, the spatial periodicity of the substrate’s surface charge and further modulation of the LC director orientation in the bulk LC can be excited by the light interference pattern [3, 4].

We found that this phenomenon can be extended for the case of hybrid LC cells, where one of the substrates possesses a surface with a micro- or nano-structure. Thus, an enhancement of the nonlinear-optical response in hybrid LC cells made on a silicon substrate with a regular micro-structure was revealed [5]. We study the photorefractive effect in hybrid LC cells that contain a substrate with a gold island film [6]. The enhancement of the nonlinear response is associated with the disturbed easy axis orientation on the scales (~50-300 nm) much smaller than that of the light interference pattern (~20÷30 µm). In addition, we find that the dynamic redistribution of the charge over the film with gold islands under the influence of both the light fringe pattern and the applied dc voltage determines the temporal characteristics of the nonlinear response. The kinetic properties of nonlinear hybrid LC cells are studied depending on the size of gold islands and the thickness of the LC layer. These properties are customizable via the appropriate choice of nano- or micro-structures on the control surface.

Hybrid nonlinear LC cells can become efficient electro-optical elements that are applicable to electro-optical signal processing and nonlinear spatial light modulators.

 

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[6] L. Viduta, T. Gavrilko, A. Marchenko, V. Nechytayko, A. Senenko, R. Fedorovich, P. Shabatyn, Structure and electroluminescent properties of thin tetracene layers on gold island films, Ukr. J. Phys. 57 (2), 260-265 (2012).