The theoretical foundation for near-field scanning optical tomography (NSOT), a method based on near-field scanning optical microscopy (NSOM) for three-dimensional optical imaging with subwavelength resolution, is presented. Analyses of the forward problem for a number of NSOM configurations with multiple-angle illuminations are described based on the vector electromagnetic theory, including reflection and transmission modes, with ideal and nonideal optical probes, etc. The first Born approximation is employed in describing scattering from a sample with low susceptibility contrast from the background. In the case of a nonideal optical probe, interaction between the probe tip and the optical field is modeled in a nonperturbative manner. A pseudoinverse solution to the corresponding linearized inverse scattering problem is constructed. The results are illustrated by numerical simulations.

Other possible modalities of NSOT are investigated. An experimental configuration with three-dimensional volumetric scan of the probe is studied for the possibility of a tomographic imaging with a fixed-angle illumination. Alternatively, a broadband illumination with one fixed angle or a limited number of angles of incidence, with coherent measurement, may be employed to obtain tomographic reconstruction. Forward and inverse analyses of these new modalities with numerical simulations are conducted.