Optical solitons in nematic liquid crystals: Arbitrary deviation angle model

Abstract

We study a coupled Schrödinger-elliptic evolution system that describes the propagation of a laser beam in nematic liquid crystals. The elliptic equation describes the effects of the beam electric field on the local orientation (director field) of the nematic liquid crystal and has an important regularizing effect, seen experimentally and understood theoretically in related models. In the present work we propose a new nonlinear elliptic equation for the director field that makes no assumption on the size of the director field angle. The analysis of this elliptic equation leads to an upper bound for the size of the director angle that we believe is optimal and physically relevant, and that implies that the elastic response of the medium prevents a complete alignment between the electric field and the orientation of the liquid crystal. The results on the elliptic problem are combined with arguments from dispersive wave theory to show the local and global well-posedness of the evolution problem and the decay of small initial conditions. We also show the existence of constrained minimizers of the Hamiltonian, assuming sufficiently large optical power ($L^2$-norm of the laser field). These minimizers are solitons with radial, monotonically decreasing profiles.