Inverse Problem of Diffraction by an Inhomogeneous Solid with a Piecewise Hoelder Refractive Index

The problem of reconstruction of an unknown refractive index $k(x)$ of an inhomogeneous solid $P$ is considered. The refractive index is assumed to be a piecewise-H\"{o}lder function The original boundary value problem for the Helmholtz equation is reduced to the integral Lippman-Schwinger equation. The incident wave is defeined by a point source located outside $P.$ The solution of the inverse problem is obtained in two steps. First, the "current" $J = (k^2 - k_0^2)u$ is determined in the inhomogeneity region. Second, the desired function $k (x)$ is expressed via the current $J (x)$ and the incident wave $u_0.$ The uniqueness of the solution $J$ to the first-kind integral equation is proved in the class of piecewise-constant functions. The two-step method was verified by solving a test problem with a given refractive index. The comparison between the approximate solutions and the exact one approved the efficiency of the proposed method.