Determination of spectrophotometer polarization and its use in rapid accurate polarized transmission measurements

Abstract

The conventional method of measuring polarized transmission components of an anisotropic material requires the insertion of linear polarizers in the beam. For commonly used dichroic polarizers, which have a limited spectral range of use, this represents a time-consuming process, particularly for measurements encompassing a wide spectral range. Since the efficiency of dichroic polarizers is typically 25-40%, there is also a sacrifice of system throughput. This paper presents a more time-efficient and sensitive method for obtaining polarized transmission data by eliminating the need of an external polarizer. The method is based on the very large degree of polarization of our Perkin-Elmer Lambda-9 double-grating spectrophotometer from 250 to 950 nm. This effect has been accurately determined with previously well-characterized dichroic polarizers over the 250-1200-nm range. Examples of its application over a 1-yr period are given. The typical agreement between this method and the conventional method is +/-0.003 transmittance units.