Apparatus for characterizing fibrous materials using stokes parameters

8 An apparatus for determining fiber orientation parameters of a sheet of material during a production process includes a polarized radiation generating system operable for providing polarized radiation having a frequency of at least 1×10Hz. The radiation is aligned to be incident on a sheet material to be characterized. A polarimeter is aligned to receive the radiation transmitted by the sheet material. A photodetector is provided for measuring radiation received after polarization processing by the polarimeter. A processor is coupled to the photodetector for calculating Stokes parameters of the sheet material based upon intensities of the radiation received and determines at least one parameter relating to fiber orientation of the sheet material based upon the Stokes parameters.