Accurate determination of fiber radii in the hypermicrometer range by multiwavelength laser light scattering.

Laser light scattering from fused silica fibers, with radii in the hypermicrometer range (1-10 microm) has been studied. The vertical polarized component of the scattered radiation has been observed over an angular range from 2 degrees to 135 degrees , the angular resolution being 0 degrees 3. The experiments were carried out using the discrete visible wavelength lines from a Kr(+) ion laser. The experimentally observed total number of minima in the angular range between 0 degrees and 90 degrees has been compared with computations based on the model of an infinitely long circular cylinder. In this way it is possible to perform a fast and accurate (better than 1%) determination of fiber radii without the necessity of calibration, over a large range of physical acceptable refractive indices. Alternatively, measuring the near forwardscattering over a carefully predetermined collecting aperture suffices to estimate quickly the fiber radius to within 5.0% over the same refractive index range. When the refractive index is known beforehand, the accuracy of both methods can be improved to within 0.5% and 2%, respectively. When a full comparison with the theoretical angular scattering curves is performed, the fiber radius is obtained with an accuracy better than 0.1%, as well as the refractive index. The full curves are calculated by Dave's computational procedure adapted for cylinders.