Nematic Liquid Crystal Optical Dispersion in the Visible-Near Infrared Range

Abstract

A commercial variable angle spectroscopic ellipsometer from J. A. Woollam Company is modified in order to make possible measurements in guiding structures. The half leaky guided mode technique is realised for liquid crystal optical dispersion measurements. Features and problems related to experimental data interpretation and error sources in the refractive index measurements are carefully analyzed, achieving a final accuracy of ±0.0002. We present the measured optical dispersion curves in the wavelength range from 0.5 to 1.7 μm for two widely studied liquid crystals, namely E7 and 5CB.

Keywords:

• ellipsometry
• half leaky guided mode
• liquid crystal
• optical dispersion model
• refractive index

Notes

¹The main reason for this is the need of confinement of the LC sample in a glass cell, so that the first layer of the multi-layer sample structure is always a glass window, irrelevant for the searched result but determining the absolute major fraction of the detected light signal.

²Our custom modification of the VASE® ellipsometer allows also the implementation of the M-line technique for the optical characterisation of solid guiding structures [9].