NUMERICAL AND EXPERIMENTAL-STUDY OF DISORDERED MULTILAYERS FOR BROAD-BAND X-RAY REFLECTION

The effect of layer thickness disorder in periodic multilayers on x-ra y reflectivity is investigated numerically and experimentally. We pres ent ensemble calculations, taking into account absorption and interfac ial roughness. It is demonstrated that layer thickness disorder yields band broadening and increased integrated reflectivity. For applicatio ns we concentrate on extrema of the ensembles, giving the highest inte grated reflectivity. We develop global optimization methods that can a lso be used to generate specified reflection band structures. In a few examples, applications of the optimization methods are discussed. To illustrate the practical applicability of the methods, we compare expe rimental realizations to the calculation. In one case we achieve a 42% increase in integrated reflectivity in the 130 Angstrom < lambda < 19 0 Angstrom spectral range with respect to a periodic multilayer with i ts first-order Bragg peak in the center of that range. Accurate contro l of layer thicknesses is our main experimental obstacle. (C) 1996 Opt ical Society of America