Measurement of local retardation in optically isotropic liquid crystal devices driven by in-plane electric field

The novel method to measure a local optical retardation has been proposed. By combining an electrically controllable birefringence (ECB) liquid crystal (LC) cell and image processing software, the local retardation of a polymer-stabilized blue phase (BP) with in-plane electric field has successfully been measured in a micrometer scale. When the optic axes of the sample and reference cells are aligned ±45° with respect to the crossed polarizers, the optical retardation of the sample is compensated by a reference ECB cell. In this geometry, the optical retardation or birefringence of micro-domains can be experimentally quantified by determining a complete compensation condition with electrically adjustable reference cell and image processing software. This method is very useful to measure Kerr constant of the BPLC more exactly and also can be applied for various samples that require a micrometer scale resolution for the measurement of optical retardation.