Nonlinear liquid crystals in periodic structures

Abstract

ABSTRACT We report optical and photoresponsive behavior of nonlinear liquid crystals in two-dimensional (2D) periodicstructure. 2D structure made of photoresist and titania is constructed by interference photolithography using gratingmask. Then azobenzene-doped nematic liquid crystal is infiltrated into these arrays, and photoresponsive behavior ofthe azobenzene-doped liquid crystal in the periodic structure is investigated. In particular, we show that the diffractionfrom these liquid crystal infiltrated grating structures can be optically modulated by an Ar + laser at 488 nm.Keywords: Nonlinear liquid crystals, confined structure, periodic arrays, diffraction 1. INTRODUCTION Nematic liquid crystals (NLC) possess very broadband [from 400 nm to 20 microns] birefringence andtransparency, and extraordinarily large optical nonlinearity [1,2]. By far the largest nonlinear refractive index changingmechanism is the optically induced reorientation of the nematic axis of aligned nematic films. Conventional methods ofaligning NLCs employ either surfactant- or rubbed-polymer coated cell windows, for homeotropic or planar alignment,respectively. In a previous publication [3], we have demonstrated that planar aligning action may also be engendered bya 1-D sub-wavelength grating inscribed on the glass windows. Furthermore, we showed that the surface gratings, incombination with the intensity dependent refractive index of the liquid crystal, could function as a nonlinear diffraction.In this paper, we report a novel method of fabricating 2-D grating structures, and observation of nonlinear diffractionfrom these structures impregnated with supra-nonlinear nematic liquid crystals [4].