SynopsisThe combination of the laser and optical diffraction analysis provides a powerful tool for the determination of fiber orientation distribution in any paper sheet of basis weight low enough to be translucent to the laser beam. The coherent light beam from the laser is diffracted by the sample. It undergoes a Fourier transform from which the orientation distributions can be calculated. Measurements were made on 14 different samples of various degrees of orientation, including an essentially random handsheet as a control. The cross-direction/machine direction elastic modulus ratios of the samples were found to correlate well with the distribution functions fitted to the orientation data. The correlation curve was S-shaped, with a drastic drop in the modulus ratio in the medium range of fiber orientation.