The information content of radiated fields and the achievable resolution limits in the reconstruction of a bounded current distribution are dealt with. The analysis refers to the scalar and one dimensional case of a rectilinear and bounded electric current distribution when data are collected over a segment location in the Fresnel or near zone, orthogonal and centered with respect to the source. In the Fresnel zone, the investigation is carried out by means of the analytical Singular Value Decomposition (SVD) of the radiation operator providing the unknown-data mapping. This has been made possible thanks to the introduction of suitable weighted scalar products both in the unknown and data spaces. In the near zone, a numerical approach based on the SVD of the radiation operator has been followed. The effect of the geometrical parameters of the measurement configuration on depth resolving power is also discussed.
A new method of doping profile reconstruction, starting from infrared spectroscopic measurements, is presented and numerically analyzed. We have developed, relying on the scattering integral equations, a new formulation allowing to directly relate the optical reflected intensity to the free carriers concentration. This formulation has been used to develop an iterative algorithm for dopant profiling. The main advantage of our approach is that the unknown dopant file is modeled by a finite series of basic functions. As the series expansion allows to describe a wide class of profiles, it is not necessary to choose a priori the functional form of the doping profile (e.g. exponential function, gaussian function, error function etc.). This allows to reconstruct the actual profile, regardless of its similarity with the expected one.
The reconstruction of dielectric properties of buried objects amounts to the solution of a nonlinear inverse scattering problem whose data are aspect limited in both space and frequency domains. We investigate how these points entails that only a limited number of dielectric profile functions can be reliably reconstructed. Moreover the influence of the model adopted to approximate the relationship between the dielectric properties of buried object and the scattered field is also pointed out, with reference to simpler canonical inverse scattering problems.
Semiconductor laser diode arrays are becoming a widespread source for a large variety of applications, ranging from telecommunications to industry. In particular, the availability of low-cost high-power laser diode arrays makes it possible their use in industrial context for material cutting, welding, diagnostics and processing. In the above applications the exact control of the beam quality plays a very important role because it directly affects the reliability of the final result. We have developed a characterization technique which, starting from total intensity measurements on planes orthogonal to the beam propagation path, is able to deduce the working conditions of each laser setting up the array. The importance of this approach is twofold. First it allows a non destructive quality control on ready-to-use laser arrays; second it may represent a powerful tool for the detection of design problems in the array itself and in the bias circuitry as well. The problem is formulated as an inverse one and the solution is found by minimizing a proper functional. Several numerical experiments have been performed and the results clearly indicate the ability of the proposed approach tin identifying specific failures in a laser diode array, such as single element power drop.
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