Abstract
A simple method for determining both the size and the refractive index of spherical transparent particles, being larger in size than the wavelength of illuminating light, is proposed on the theoretical basis of geometrical optics of light scattering. In the theory, the intensity distribution of scattered light at a certain off-axis angle range of a few degrees can be recognized as interference fringes due to two dominant light rays from the particle. The ratio between the interference fringe contrasts of the scattering patterns in parallel and perpendicular polarization components is used to determine the refractive index of particles, whereas the size of particles is evaluated from the fringe pitch. Experiments were performed to confirm the validity of the proposed method. The validity range of the method is also discussed in terms of the light rays scattered into the observation angle. The present method has the advantage that measurements of the absolute intensity are not required to obtain the size and the refractive index of particles.