Systematic errors in the high-accuracy universal polarimeter: application to determining temperature-dependent optical anisotropy of KDC and KDP crystals

Abstract

The problem of removing the characteristic parasitic errors of the high-accuracy universal polarimeter method in a linearly birefringent and optically active crystal section is examined. The use of constant parasitic errors typical of each particular polarimetric system is shown to be inappropriate. The parasitics should preferably be determined in each measurement process, since the instrumental parasitics depend not only on the optical and mechanical elements of the experimental system (polarizers, rotators, detection unitetc.), but on sample quality, alignment of the system, and even in many cases on exactly where the light beam passes through the sample. Thus, measurements with different samples give different values of parasitic errors. Such instrumental parasitics can be held within the same order of magnitude for different samples (∼10−4) if they are of good optical quality. However, the parasitics are increased by an order of magnitude (∼10−3) when the samples are of moderate or bad optical quality. Optical anisotropy properties as coefficients of thermal variation of the birefringence of KDC and KDP single crystals and the optical activity of KDP at 632.8 nm wavelength are obtained, in the ranges from room temperature to 353 K and to 373 K, respectively.