polarization interferometric architectures , preferably plane mirror types , having first and second measurement legs are provided with retardation elements , preferably , at least one set of split waveplates , comprised of two segments , tilted slightly in opposite directions with respect to each other to reduce the effects of undesirable ghost beams that otherwise would travel along the same path as the principal beams to produce significant cyclic errors . with the use of the split waveplates , double reflection ghost beams have net tilts relative to the principal measurement beam , and therefore do not contribute to interference effects . this effectively eliminates waveplate ghost reflections as a source of error . use of the such split , tilted waveplates may be made in a variety of polarization interferometers including , but not limited to , uncompensated plane mirror , high stability plane mirror , differential plane mirror , double differential plane mirror , and dual linear / angular types .