Higher–Order Bragg Reflection Colors in Polymer–Stabilized Cholesteric Liquid Crystals

Abstract

The dynamic electro‐optic (EO) response of polymer‐stabilized cholesteric liquid crystals prepared using unpolarized UV light (U–PSCLC), such as reflection bandwidth broadening and either red or blue tuning of the reflection peak, has been previously reported. Herein, recent efforts to use a polarized single argon‐ion laser beam to create PSCLCs (L–PSCLCs) with higher‐order reflections are described. The L–PSCLCs exhibit a primary reflection peak in the near‐infrared (NIR) regime and a second‐order reflection band with a narrow bandwidth in the visible regime that results from a deformed in‐plane CLC helical structure. The initial positions of the reflection bands are adjusted by the chiral dopant concentrations of the CLC mixture, and red, green, and blue reflection colors from the second‐order Bragg reflection are demonstrated. The primary and the second‐order reflection bands can be shifted to longer wavelengths by application of a DC electric field. The reflection efficiency of the higher‐order reflection notch increases with polymer concentration, which affects the degree of in‐plane deformation and fixation of the CLC helix. Modeling is used to further explain the formation of the higher‐order reflection bands of PSCLCs observed experimentally.

Keywords

• cholesteric liquid crystals
• deformed cholesteric helix
• higher order Bragg reflections
• polymer stabilization