Surface-mediated non-linear optical effects in liquid crystals

TL;DR

This paper presents a phenomenological model of two-beam optical interactions in liquid crystal cells, highlighting how surface potential modulations influence diffraction and energy exchange, with implications for optimizing non-linear optical effects.

Contribution

It introduces a new model linking surface potential modulation to optical diffraction and energy exchange in liquid crystal photorefractive systems.

Findings

Energy exchange is highly sensitive to beam angles and applied potential.

Surface potential modulation creates a grating affecting light diffraction.

The model suggests ways to optimize non-linear optical interactions.

Abstract

We make a phenomenological model of optical two-beam interaction in a model planar liquid crystal cell. The liquid crystal is subject to homeotropic anchoring at the cell walls, is surrounded by thin photosensitive layers, and is subject to a variable potential across the cell. These systems are often known as liquid crystal photorefractive systems. The interference between the two obliquely incident beams causes a time-independent periodic modulation in electric field intensity in the direction transverse to the cell normal. Our model includes this field phenomenologically by affecting the potential at the walls of the cell. The transverse periodic surface potential causes spatially periodic departures from a pure homeotropic texture. The texture modulation acts as a grating for the incident light. The incident light is both directly transmitted and also subject to diffraction. The first diffracted beams result in energy exchange between the beams. We find that the degree of energy exchange can be strongly sensitive to the mean angle of incidence, the angle between the beams, and the imposed potential across the cell. We use the model to speculate about what factors optimize non-linear optical interaction in liquid crystalline photorefractive systems.