Production of broad band AR coatings with total reoptimization of layer thicknesses

The present thesis describes experimental studies of fabrication of high performance broad band anti-reflection (AH) coatings with Jon Beam Sptrttering (IBS) deposition technique. The fabrication of complex optical multilayer coatings are difficvmlt because the layer thicknesses and optical indices of the individual layers differ from the desired values for various reasons of the fabrication process. And the tolerances on the layer thicknesses and refractive indices in broad band AR coatings are often strict, and small deviations may ruin the performance of the multilayer. Therefore, there is a necessity for a method that would compensate for the discrepancies. To fill this need, reoptimization techniques must be considered, which determine errors of all layers after the first complete deposition, and run the second with reoptimized design. The error determination process is a kind of problem to find the minimtum of a function, and it is very complex because of the great number of local minima. In this thesis, a reoptimization method to determine and refine deposition errors of multilayers is described. And the results of numerical simulations on the effectiveness of various reoptimization strategies are presented. It is emphasized that adding some kinds of restrictions is effective to avoid the local minima problenn. To demonstrate the performance of tire method, several kinds of broad band AR coatings were fabricated. The theoretical and measured spectral reflectance curves of these multilayers closely agree with one another over broad spectral regions. And types and causes of multilayer during deposition are discussed. In Chapter 1, a historical backgrourad and the purpose of the present study is outlined, In Clnapter 2, examples of broad band AR coating design and its dependexace on the number of layers, film materials, and deposition errors are presented. And the need for reoptimization is emphasized. In Chapter 3, deposition error determination techniques to improve the actual performance of broad band AR coating using Simulated Annealing are described. It is shown that the simtulated annealing method is effective in the field through numerical simulations. In Chapter 4, the results of experiments of the performance improvement mentioned in previous chapters are described. And it is shown that the designed and measured spectral reflectance curves of these mtultilayers closely agree with one another over broad spectral regions as the result of the improvement. In Chapter 5, several aspects of the deposition error with IBS are discussed. It is emphasized that accurate measurement is necessary for further performance improvement. In Chapter 6, main conclusions obtained throughout the present study are summarized, and remaining problems to be solved in future are described