Defect formation in N* LCs via photovoltaic fields: impact of surface treatment

ABSTRACT

Field-induced defect creation was investigated in chiral nematic liquid crystal test cells, where a Fe-doped lithium niobate thin-cut was applied as field generating substrate. These photo responsive test cells were exposed to focused continuous wave laser light, which resulted in the formation of localised defects. The covering indium tin oxide coated glass of the test cells was treated with a polyvinyl alcohol alignment layer. This alignment layer was either applied with a doctor blade technique or by spin casting of a polyvinyl solution, which was thermally annealed, subsequently. The surface roughness of the alignment layers was investigated with atomic force microscopy, which was interesting to understand how defects and locally lying helices were supported or suppressed in various samples. Well-confined circular defects were formed in test cells with spin-casted alignment layers and the appearance and unwanted interaction with oily streaks could be efficiently reduced in these samples. The results are promising. Samples with an oily streak-free homogenous standing helix orientation of the chiral nematic liquid crystal are an ideal canvas for rewritable pattern formation in a chiral nematic LC: Such samples have high potential as reconfigurable diffractive elements such as rewritable diffraction gratings.

Graphical Abstract

KEYWORDS:

• Localised defect formation
• chiral nematic liquid crystals
• iron doped lithium niobate
• nonlinear optics

Additional information

Funding

Funding by the German Research Council (DFG) grant [LO 1922/4-1]and by the US Air Force Office of Scientific Research (AFOSR) grant [FA9550-18-1-7002] are grateful acknowledged.