A New Optical Method to Measure Angular Tilts for Planar Anchored Nematic Liquid Crystals

We present a new optical method to measure the small tilt angles of quasi-planar anchored nematics. We use an hybrid nematic cell which contains twin domains of different birefringence for non zero tilt. We measure the small rotation of the cell which equalize the twin domains birefringence, at a common border. This rotation is proportional to the tilt. The calibration constant can be calculated from the knowledge of the elastic constants anisotropy and the refractive indices, or independently measured from a known tilted anchoring plate. The method is linear in angle, i.e. sensitive and independent of the sample thickness. Comparative measurements of tilt on PVA and SiO are presented and discussed, using this method and other optical measurements of birefringence.