Simple model for estimating band edge wavelengths of selective reflection from cholesteric liquid crystals for oblique incidence.

A simple model for estimating band edge wavelengths of selective reflection from cholesteric liquid crystals (CLCs) for oblique incidence is proposed. The proposed model and calculation method are based on a geometrical optics model and Bragg's law. Average refractive indices and Bragg angles in a CLC for the short- and long-wavelength edges of a reflection band are calculated using the model. The band edge wavelengths are determined by substituting the average refractive indices and Bragg angles into Bragg's law. The angular dependences of the band edge wavelengths show good agreement with those calculated by Berreman and Scheffer's [Phys. Rev. Lett. 25, 577 (1970)10.1103/PhysRevLett.25.577] 4×4 matrix method. Although the derived equations are not exact solutions of Maxwell's equations, the proposed method can approximately predict the angular dependences of the center wavelength, bandwidth, and band edge wavelengths of the selective reflection in CLCs.