Near-field subsurface electromagnetic tomography and holography
Methods of multifrequency tomography and holography of subsurface dielectric inhomogeneities in the near-field zone based on the solution of inverse scattering problem are studied from the viewpoint of their applicability for targets with strong dielectric contrasts or with a complicated internal structure. Results based on numerical simulation with input data calculated from Maxwell equations are presented.
Pseudopulse near-field subsurface tomography.
Decisive success has been achieved in developing the subsurface near-field scanning tomography that overcomes the Rayleigh diffraction limit of a resolution. It is related to the transformation of the multifrequency inverse scattering problem to that for a complex-valued synthesized pulse (pseudopulse). It leads to the integral equation that has maxima in the depth dependence of its kernel and, hence, to the much better depth resolution of tomography. Moreover, the noise related to surface scattering is mainly suppressed in such an approach. This idea is realized here in the microwave subsurface tomography of 3D inhomogeneous dielectric structures. For homogeneous dielectric targets, this approach is applied to obtain holography images of their shape.
Reflectometry sounding of inhomogeneities in periodic multilayer structures
In this paper, a reflectometry method of sounding of layers' parameters in periodic multilayered dielectric structures is proposed and applied to the study of X-ray optics structures. It is based on angular and spectral (multi-frequency) measurements of a studied structure. Angular measurements of the reflection coefficient are used to determine the period of a structure; the spectrum is in use to study the inhomogeneity of layers - the effective profile of dielectric permittivity related to the diffusion of material at the epitaxy and to the roughness of layers' interfaces. An integral equation has been obtained to solve this inverse scattering problem. An algorithm of the solution based on the Tikhonov's method of generalized discrepancy has been worked out, and the theory has been applied to study inhomogeneities of multilayer structures manufactured for the X-ray optics.