ABSTRACT
Throughout this book retardance has proven to be one of the more difficult concepts to define. The retardance of a compound retarder (formed from several birefringent plates) can, for example, vary continuously from 1½ waves to 2½ waves of retardance without ever passing through 2 waves of retardance! Retardance can simultaneously assume multiple values when the fast axes of birefringent components are not parallel or perpendicular to each other. Measured data verifies this complex but fascinating issue. Modeling of compound multi-order retarders is addressed in this chapter.
Also, the operation of retardance unwrapping of the principal retardance is developed to explain the behavior of retardance of the compound retarders. This allows us to generalize the concept of retarder order for what at first appears to be mysterious jumps in the retardance.
Two approaches to retardance discontinuities are developed to explain this complex concept. One approach uses a dispersion model to describe the retardance behavior. Another approach considers multiple wavefronts exiting the compound retarder system i.e., a multi-valued optical path length (OPL) view.
