Patent ID: 7289210

Claim:
A method for determining relative phase retardations and orientations of the optical axes of different layer in a multi-layered birefringent cellulosic fibre specimen comprising the steps of: producing a circularly polarized light beam having a plurality of well-defined wavelengths, wherein the plurality is at least the same number as the number of parameters to be determined in the multi-layered specimen under evaluation; disposing said multi-layered birefringent cellulosic fibre specimen in said circuhrly polarized light beani in a non-restricted orientation; impinging the circularly polarized light beam on the multi-layered birefringent cellulosic fibre specimen; recording and measuring the light intensities of the plurality of well-defined wavelengths emergent from a circular analyzer located after the specimen; determining the relative phase retardations and orientations of the optical axes of different layers of the specimen from the light intensities of the emergent wavelengths by fitting the data with an equation that describes the specimen; and assessing the cellulosic fibre for use in a cellulosic fibre product based on the determination of the relative phase retardations and orientations of the optical axes of different layers of the specimen.