Demonstration of wavelength-swept laser using cholesteric liquid-crystal cavity and its application for laser scanning.

A cholesteric liquid-crystal gel (ChLCG) is fabricated by photopolymerizing a ChLC doped with a mesogenic monomer at a high concentration of 38.2 wt%. The reflection band of the ChLCG exhibits a fast, continuous, and time-varying wavelength shift of the order of kilohertz by applying a sine wave voltage. Swept lasing at a swept rate of 100 Hz and with a swept range of 12 nm can be achieved by irradiating a dye-doped ChLCG with a quasi-continuous-wave laser. When the swept laser light is introduced to a diffracting grating, a laser scanning device is demonstrated.

Thickness-independent dynamics in cholesteric liquid crystals.

We report fast electro-optic response independent of cell thickness in cholesteric liquid crystals (ChLCs). Usually, an electric field normal to the helix axis of ChLCs induces two fast and one slow response components: helical elongation (slow one), helical deformation (fast one), and flexoelectric effect (fast one). In this study, we found that a planarly aligned ChLC applied with an in-plane electric field exhibited only fast response components because the glass substrates suppressed the motion of the helical elongation. Furthermore, we demonstrated complete separation of the remaining fast components by using dielectric measurement system. Consequently, we were able to analyze dynamics of the helical deformation in detail, in which response times exhibited quadratic dependence on the helical pitch and no dependence on the cell thickness.

Dynamic control of colorful reflection toward practical cholesteric liquid crystal displays.

We investigated the possibility of practical applications using cholesteric liquid crystals (ChLCs) with Helfrich deformation, which causes the undulation of the helical structure. Usually, the Helfrich deformation is very unstable and can be obtained only in the transient state for a short time (< 10 s) under continuous field application. Here, we found that a ChLC polymerized with spatial pattern distribution exhibited high durability of the Helfrich deformation. Furthermore, we revealed molecular alignment of the Helfrich deformation by scanning electron microscope. Finally, we fabricated a switching device embedded with color-tunable reflection pixels to exhibit potential of reflective display application.

Tunable lasing from a cholesteric liquid crystal film embedded with a liquid crystal nanopore network.

Continuous tuning of lasing wavelength is achieved in cholesteric liquid crystal lasers by embedding a network of nanopores with an average size of 10 nm filled with liquid crystals inside a polymerized matrix with helical order. The device possesses both high transparency and a fast response time because the tuning is driven by local reorientation of the liquid crystal molecules in the nanopores.