Broadband x-ray optical elements based on aperiodic multilayer structures

An investigation was made of the potentialities of aperiodic multilayer structures (AMSs) optimised to obtain a preassigned reflection spectrum in the x-ray range (λ < 300 Å) and also starting from other criteria. It was found that among the multitude of realisations of AMSs there exist those which are superior to the regular structure in width of the operating range, integral reflectivity, and peak reflectivity. New types of x-ray optical elements are proposed on a basis of AMSs. AMSs were derived which possess a constant normal-incidence reflectivity R at normal incidence throughout the 130 — 190 Å (R = 24 %), 130 — 300 Å (R = 15%), etc., ranges. We found AMSs which possess a high polarising power (polarisance) and a constant R in a broad wavelength range for a fixed angle of incidence. AMSs possessing several isolated reflection peaks which are not Bragg peaks of one another, were calculated. AMSs intended for operation in the hard x-ray range at grazing incidence of radiation were optimised. The technique elaborated in our work was demonstrated to be efficient for optimising AMSs with a very large (~10³) number of layers.