IMAGING OF A ROTATIONALLY SYMMETRICAL DIELECTRIC CYLINDER BY A QUADRATIC APPROACH

A quadratic approximation of the electromagnetic scattering equation i s used to solve the inverse problem of the reconstruction of the diele ctric permittivity function of a rotationally symmetric cylindrical ob ject embedded in a homogeneous medium and illuminated by an incident p lane wave at fixed frequency. The problem is formulated as the minimiz ation of a properly defined functional. Because the operator involved in the inversion is quadratic, it is possible to discuss and avoid the presence of local minima (a well-known problem in nonlinear inversion ). Theoretical considerations and numerical examples show the advantag es of using a quadratic model in comparison with a linear one. (C) 199 7 Optical Society of America.