Chiral nematic liquid crystal microlenses

Abstract

Nematic liquid crystals (NLCs) of achiral molecules and racemic mixtures of chiral ones form flat films and show uniform textures between circular polarizers when suspended in sub-millimeter size grids and immersed in water. On addition of chiral dopants to the liquid crystal, the films exhibit optical textures with concentric ring patterns and radial variation of the birefringence color. Both are related to a biconvex shape of the chiral liquid crystal film; the rings are due to interference. The curvature radii of the biconvex lens array are in the range of a few millimeters. This curvature leads to a radial variation of the optical axis along the plane of the film. Such a Pancharatnam-type phase lens dominates the imaging and explains the measured focal length of about one millimeter. To our knowledge, these are the first spontaneously formed Pancharatnam devices. The unwinding of the helical structure at the grid walls drives the lens shape. The relation between the lens curvature and material properties such as helical pitch, the twist elastic constant, and the interfacial tensions, is derived. This simple, novel method for spontaneously forming microlens arrays can also be used for various sensors.

Stimuli‐Driven Control of the Helical Axis of Self‐Organized Soft Helical Superstructures

“…When the pitch of a CLC corresponds to the wavelength of visible light, it appears colored. CLCs have found applications in thermography for temperature sensing, reflective displays, pressure, gas, humidity and biosensing, tunable color filters, polarizers, mirrorless lasing, beam steering, switchable smart windows for controlling interior temperature and brightness, fast and high contrast flexoelectro‐optic devices, and amplification of photon upconversion . Other applications include their use as chiral solvents for the synthesis of helical conducting polymers such as polyacetylenes, dynamic photomasks for photolithography, chiral templates for the fabrication of iridescent functional materials, and smart coatings for switchable surface topographies toward controllable friction and adhesion …”

Термомеханический Режим Формирования Вихревых Течений В Гибридно Ориентированном Нематическом Канале

“…В последнее время все чаще методы микро-и нанофлуидистики находят применение не только при исследовании процессов транспортировки и сортировки нанолитровых объемов молекулярных жидкостей [1][2][3][4], но и в разнообразных семействах сенсоров и датчиков на основе термо-и лиотропных жидкокристаллических (ЖК) материалов [3,5]. Еще одной не менее интригующей областью применения микролитровых объемов ЖК-материалов являются биометрические оптические системы, где основным элементом являются ЖК-линзы с регулируемым фокусным расстоянием (tunable liquid crystal microlenses) [6,7]. Один из способов, позволяющий манипулировать такими микроразмерными молекулярными системами, основывается на использовании электрического поля [8].…”

Circular Polarization and Wavelength Selective Gratings Based on Holographic Cholesteric Liquid Crystal Templates

“…Cholesteric liquid crystal (CLC) is a soft matter with a selforganized helical structure and can be regarded as a onedimensional photonic crystal [1]. It has multiple responses under various external stimuli and can thus be applied on tunable photonic devices, such as tunable optical filter [2], diffraction grating [3], mirror-less laser [4], microlens [5], and eye protector [6]. CLCs can exhibit various textures, including planar (uniformly standing helix), fingerprint (uniformly lying helix), and focal conic, depending on the orientation of the helical axes in CLCs.…”