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Title: Electrically tunable total reflection of light by oblique helicoidal cholesteric
Abstract

An oblique helicoidal state of a cholesteric liquid crystal (ChOH) is capable of continuous change of the pitch$$P$$Pin response to an applied electric field. Such a structure reflects 50% of the unpolarized light incident along the ChOHaxis in the electrically tunable band determined by$$P$$P/2. Here, we demonstrate that at an oblique incidence of light, ChOHreflects 100% of light of any polarization. This singlet band of total reflection is associated with the full pitch$$P$$P. We also describe the satellite$$P/2$$P/2,$$P/3$$P/3, and$$P/4$$P/4bands. The$$P/2$$P/2and$$P/4$$P/4bands are triplets, whereas$$P/3$$P/3band is a singlet caused by multiple scatterings at$$P$$Pand$$P/2$$P/2. A single ChOHcell acted upon by an electric field tunes all these bands in a very broad spectral range, from ultraviolet to infrared and beyond, thus representing a structural color device with enormous potential for optical and photonic applications.

Impact statement

Pigments, inks, and dyes produce colors by partially consuming the energy of light. In contrast, structural colors caused by interference and diffraction of light scattered at submicrometer length scales do not involve energy losses, which explains their widespread in Nature and the interest of researchers to develop mimicking materials. The grand challenge is to produce materials in which the structural colors could be dynamically tuned. Among the oldest known materials producing structural colors are cholesteric liquid crystals. Light causes coloration by selective Bragg reflection at the periodic helicoidal structure formed by cholesteric molecules. The cholesteric pitch and thus the color can be altered by chemical composition or by temperature, but, unfortunately, dynamic tuning by electromagnetic field has been elusive. Here, we demonstrate that a cholesteric material in a new oblique helicoidal ChOHstate could produce total reflection of an obliquely incident light of any polarization. The material reflects 100% of light within a band that is continuously tunable by the electric field through the entire visible spectrum while preserving its maximum efficiency. Broad electric tunability of total reflection makes the ChOHmaterial suitable for applications in energy-saving smart windows, transparent displays, communications, lasers, multispectral imaging, and virtual and augmented reality.

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Award ID(s):
2122399
NSF-PAR ID:
10518191
Author(s) / Creator(s):
; ; ; ; ;
Publisher / Repository:
Cambridge University Press (CUP)
Date Published:
Journal Name:
MRS Bulletin
Volume:
49
Issue:
9
ISSN:
0883-7694
Format(s):
Medium: X Size: p. 835-850
Size(s):
p. 835-850
Sponsoring Org:
National Science Foundation
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