An approach to the theory of X-ray multilayers with graded period

A wide bandpass for multilayer mirrors can be obtained by gradually changing their period. In this paper the theory of such optical elements is developed on the basis of the general theory of wave propagation through layered medium. The results of reflectivity calculation for broadband mirrors are presented. The suggested theory is a natural step to the inverse problem – design of multilayers with the required wavelength dependence of reflectivity.