Optically guided mode study of nematic liquid crystal alignment on a zero-order grating

Area of Science:

• Materials Science
• Optics
• Condensed Matter Physics

Background:

• Liquid crystal cells are crucial for display technologies.
• Characterizing their optical properties under electric fields is essential for performance optimization.
• Understanding director profiles and anchoring is key to controlling liquid crystal behavior.

Purpose of the Study:

• To characterize a liquid crystal cell using an optically guided mode technique.
• To quantify the optical director profile of nematic liquid crystal E7 under electric fields.
• To determine azimuthal anchoring strength and bulk twist elastic constants.

Main Methods:

• Utilized an optically guided mode technique with a zero-order diffraction grating and polyimide-coated substrate.
• Excited fully leaky guided modes within the liquid crystal layer.
• Fitted angle-dependent optical data to multilayer optical theory.

Main Results:

• Quantified the optical director profile under weak in-plane electric fields.
• Accurately determined the twist profile of the liquid crystal for varying field strengths.
• Precisely determined azimuthal anchoring strength and bulk twist elastic constant by comparing with elastic continuum theory.

Conclusions:

• The optically guided mode technique accurately characterizes liquid crystal cells.
• Elastic continuum theory with Rapini-Papoular anchoring effectively models liquid crystal behavior.
• Surface and bulk order parameters can be deduced by temperature-dependent measurements.