Self-induced negative refraction in nematic liquid crystals

Piccardi, A., Alberucci, A., Kravets, N., Buchnev, O. and Assanto, G. (2015) Self-induced negative refraction in nematic liquid crystals. In Proceedings 2015 European Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, CLEO/Europe-EQEC 2015. Optical Society of America..

Abstract

Negative refraction in optics is a fascinating phenomenon stemming from peculiar boundary conditions and momentum conservation at a dielectric interface. In natural dielectrics it can only be observed in anisotropic media, where the incident and refracted Poynting vectors can lay in the same half-plane with respect to normal incidence [1]. Due to their high (usually positive) anisotropy, nematic liquid crystals (NLC) [2] are ideal media where negative refraction can be observed; moreover, their optical reorientational response allows to tune both linear and nonlinear properties in the non-perturbative regime, exploiting the torque exerted on the field-induced molecular dipoles [3]. In NLC the optic axis is defined by the molecular director, i.e. the average orientation of molecular long axes; if we consider a beam impinging on the NLC sample, as for a positive uniaxial, the Poynting vector always lays in between the director and the wave vector. In the highly nonlinear regime, the torque can be strong enough to rotate the director and modify the linear properties [4]; the director rotation causes a redirection of the Poynting vector and, if the reorientation is large enough, the refracted beam can be steered in the same half-plane of the incident beam, i.e. undergo negative refraction.

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