Observations of Electrically Surface-Induced Regular Arrays of Focal Conies in a Homeotropic NPOB Smectic A Liquid Crystal

Regular arrays of confocal pairs of ellipse-hyperbola with Marignan-Malet-Parodi association were observed in the boundary regions of a smectic A NPOB liquid crystal after cooling of a homeotropic nematic layer subjected to the action of a transversal high-frequency electric field with a sufficient strength. These smectic A textures exist as a storage mode after the removal of the electric field. Their distribution and sizes depend on the surface energy which has been determined to be in the range of 5 × 10−3 erg/cm2 for a clear or lecithin-coated glass plate. In hybrid-aligned planar-homeotropic smectic A layers under the same conditions simultaneously exist parabolic focals and edge-dislocations near the glass plate where the surface orientation is planar and regular arrays of confocal pairs of ellipse-hyperbola near the glass plate where the surface orientation is homeotropic. The regular arrays of confocal domains might be used as diffraction gratings whereas the nonregular strong-scattering arrays obtained at lower electric fields might be used in the indicator technique.