Dynamic Pattern Formation and Beam-Steering Characteristics of Cholesteric Gratings

Abstract

The dynamic pattern formation and the beam-steering characteristics of cholesteric gratings were studied. Films with a planar cholesteric texture and various thickness to pitch length ratios (d/p) were fabricated. An optical microscope was used to observe the stripe patterns of the cholesteric gratings formed by applying a voltage to the planar films. The micrographs showed that the cholesteric gratings were formed in two different ways, depending on the sample's d/p ratio. For samples with 1/2≤d/p≤1.0, the grating stripes simultaneously appeared across the whole sample, and the contrast of the stripes increased with time during formation. For films with d/p≥1.5, the stripes were initiated near the edges, and near the defects on the substrates, and then slowly extended to the whole sample along the rubbing direction. The diffraction measurements showed that the diffracted beams could be steered either electrically or optically only for the latter type of film. These results can be well explained theoretically.

Rotatable Diffraction Gratings Based on Cholesteric Liquid Crystals with Phototunable Helix Pitch

“…[ 19,22 ] This approach provided good agreement with the experimental data (solid red lines on polar diagrams in Figure 4 , see also Figure S4, Supporting Information), but only qualitatively, and did not explain the jump-like behavior. To our knowledge there is no model describing the relationship of the helix pitch and a period of undulations of cholesteric layer under hybrid (homeotropic -planar) boundary conditions.…”

“…[ 19 ] In order to avoid this effect during the grating rotation we used a circularly polarized probe beam. It is known that the effi ciency of diffraction on phase cholesteric gratings depends on the direction of polarization of linearly polarized light and the most effective diffraction occurs for the light with perpendicular polarization with respect to the grating vector.…”

“…[ 32,33 ] Careful examination of the kinetic curves revealed the complicated character of the grating period changes upon irradiation, while the monotonic growth of rotation angle occurred. Previously, so called vertically aligned LC layer model instead of conventional middle-LC layer model [ 19 ] was proposed by Lin. It is possible to distinguish the "fl at" areas where the period does not change signifi cantly upon the exposure and the areas of the rapid period growth (or jump-like behavior).…”

“…[15][16][17][18][19][20][21][22][23][24][25][26][27][28] There are several principally different ways to produce the phase gratings in CLC. [15][16][17][18][19][20][21][22][23][24][25][26][27][28] There are several principally different ways to produce the phase gratings in CLC.…”

Dynamic Control of Light Direction Enabled by Stimuli‐Responsive Liquid Crystal Gratings

“…[227,228] Accordingly, for 0.5 <d/P < 1.0, the stripes appear everywhere simultaneously across the sample like the development of a photography which is referred to as developable modulation (DM). [227,228] Accordingly, for 0.5 <d/P < 1.0, the stripes appear everywhere simultaneously across the sample like the development of a photography which is referred to as developable modulation (DM).…”