Simple Method for Measuring Small Retardance

Small retardances are encountered in many experimental works. Internal stresses, weakly birefringent materials, optical windows and formation of contaminating surface layers are sources of small retardances. Most known methods for retardance measurements fail to determine accurately their values which are sometimes essential in the evaluation of experimental results. In this work, we present a method for accurate measurement of a small retardance. Our study aims to find the retardance error in a birefringent full-wave plate which, if perfect, is considered as of zero retardance. Our treatment will make use of a previously presented model for simultaneous calibration of two phase plates.