New formulas for phase retardance measurements of birefringent plates

Two simple formulas are introduced that allow for simultaneous determination of the phase retardances of two birefringent plates from a single pair of readings of the polarizer and the analyzer at extinction. These formulas are of great importance since they furnish the basis of a model for a simple, timesaving and accurate method for calibrating phase plates in the Senarmont compensator arrangement without requiring an exact lambda4 plate and with almost direct results. The Poincaré sphere representation of polarization states is used to illustrate the model.