Validity of weak-scattering models in forward two-dimensional optical scattering.

The exact solution for scattering from cylindrical objects is compared with the following weak-scattering models: the first Born approximation, the Rytov approximation, the straight-ray model of geometric optics, and ray tracing. Computer calculations of the various approximate and the exact virtual fields at the center of a transparent cylinder are compared in order to find the practical limitations of the various approximations with respect to cylinder radii and indices of refraction. It is found that the Rytov approximation introduces a phase error that increases linearly with the cylinder radius. The straightray model yields better results than the first Rytov approximation for all cylinder radii and real indices of refraction, even at the edges. The first Born approximation is best for cylinders with radii less than a wavelength.