The Poincare sphere representation of polarization stares is used to derive
two auxiliary equations for phase retardance measurements. These equations
, in addition to another two previously derived equations, allow for extend
ing the range of validity of a model for calibrating phase plates in pairs.
In another application, the sphere is used to explain a new method for ide
ntifying the principal axes of two birefringent phase plates during their c
alibration. (C) 2000 Elsevier Science Ltd. All rights reserved.