Study of the systematic errors in HAUP measurements

A phenomenological model is proposed to account for the systematic errors c haracteristic of the NAUP (high-accuracy universal polarimeter) technique. The model is based on the assumption that the sample surface possesses effe ctive dichroic properties dde to polishing, inhomogeneities or differential Fresnel reflection. It is found that there is a sample contribution both t o the parasitic ellipticities of the polarizers and to the so-called delta Y error. This contribution adds to those which are intrinsic to the optical device. Measurements are presented in three test materials: LiNbO3, Rb2ZnC l4 and SiO2. The results are interpreted in the light of the proposed model . For the first two materials the surface effects are visible in the form o f spurious linear dichroism and residual ellipticity. For the third case, t he problem of multiple reflections arises, since the sample had a high degr ee of plane parallelism. The influence of these additional contributions is eliminated experimentally. Finally, in view of all the results, some crite ria are established for the sample optimization in HAUP measurements.