LIGHT SCATTERING FROM LARGE FIBERS AT NORMAL INCIDENCE

The high intensity at 6328 A and excellent collimation of a helium-neon maser make easy the comparatively high resolution light-scattering measurements necessary for studying the angular dependence of scattering from a single cylinder the diameter of which is significantly larger than the wavelength of light. The angular dependence of scattering from conducting (absorbing) cylinders, d = 6.27μ (9.9λ) to d = 49.9μ (78.8λ) in diameter, is described quite well by the Fraunhofer diffraction equation. Scattering from dielectric (transparent) cylinders, d = 2.23μ (3.5λ) to d = 29.37μ (46.4λ), is described better (but far from correctly) by the Fraunhofer diffraction equation, sin2, x x2, than by the approximate scattering functions for cylinders, [ 2J1(x) x]2 and [J0(x)]2, where x = (2 d/λ) sin θ/2. Rayleigh's equations seem to fit the experimental data in some detail over short ranges of scattering angle (over a few maxima and minima) if fitting parameters, diameter d and refractive index m, are selected properly. Therefore, Rayleigh's equations probably can be regarded as exact in representing experiment, at least for single dielectric cylinders. The inability to represent the experimental data over all scattering angles with a single set of parameters may arise from the sensitivity of Rayleigh's equations to parameters m and d coupled with imperfect geometry or inhomogeneities in refractive indices of fibers or both of the latter. Rayleigh's equations do not approach the Fraunhofer diffraction equation at scattering angles as small as that of the first observed minimum in the intensity versus scattering angle curve. The angle of the first minimum for dielectric cylinders is strongly dependent upon refractive index as shown by data analyses using Rayleigh's equation and inferred from scattering and diameter measurements on fibers. © 1969.