Aperiodic normal-incidence antimony-based multilayer mirrors in the 8-13-nm spectral range

The optical properties of several materials were analysed from the standpoint of fabrication of broadband normal-incidence multilayer mirrors possessing maximal uniform reflectivity in the 8 - 13-nm range. By solving the inverse problem of multilayer optics we show that aperiodic Sb/(B4C,Sc,Si) multilayer structures optimised for maximum uniform reflectivity in the 8 - 13-nm range are able to afford a normal-incidence reflectivity R similar to 10% throughout this range. The best results are exhibited by the pair Sb/B4C, for which the average reflection coefficient amounts to about 13%. The dependence of optimisation result on the program-mable limitation on the minimal layer thickness in the multilayer structure was numerically investigated. An empirical rule was established where by setting the lower bound for a layer thickness at a level similar to lambda(min)/4 (in this case, lambda(min) = 8 nm) does not result in an appreciable lowering of attainable uniform reflectivity.