Optical imaging of the effect of in-plane fields on cholesteric liquid crystals

The effects of in-plane electric fields on the director structure of cholesteric liquid crystals has been imaged in three dimensions using fluorescence confocal polarizing microscopy. The results show that a liquid crystal lying outside the electrode gap can be significantly affected by stray fields occurring above the electrode surface, resulting in a 90° rotation of the cholesteric helix. Distinct differences between the behavior of cholesterics with positive and negative dielectric anisotropies are observed.

Figure 1

(Color online) Schematic diagram of the arrangement of optical components in a fluorescence confocal polarizing microscopy system.

Figure 2

(Color online) Schematic diagram of a typical in-plane switching homogeneously aligned liquid crystal cell for use in the FCPM imaging study.

Figure 3

(Color online) Cross-section images from a $\mathrm{ZLI}\text{−}2293$ liquid crystal cell showing the fluorescence intensity as a function of position at applied peak-to-peak voltages of (a) 0, (b) 15, (c) 25, and (d) $50\mathrm{V}$.

Figure 4

(Color online) Cross-section images from a $\mathrm{MLC}\text{−}6608$ liquid crystal cell showing the fluorescence intensity as a function of position at applied peak-to-peak voltages of (a) 0, (b) 40, (c) 60, and (d) $100\mathrm{V}$.

Figure 5

(Color online) Comparison of recorded fluorescence intensity (arbitrary units) versus depth into the sample for regions above the silver electrode and glass electrode gap.

Figure 6

Modeled electric field for a $25{\mathrm{V}}_{pp}$ in-plane potential difference applied across a $25\mu \mathrm{m}$ gap. The gray scale indicates the electric field intensity and the arrows indicate the corresponding field lines.