Aperiodic multilayer mirrors for efficient broadband reflection in the extreme ultraviolet

Abstract : Recent extreme ultraviolet sources using high-harmonic generation in a rare gas make new optics developments necessary. We report on the study and development of multilayer structures with efficient reflectivity in the 35–75 eV energy range. We have optimized, deposited and characterized two aperiodic broadband mirrors consisting of a Mo, Si and B4C thin-film stack. We used the needle procedure in order to optimize mirror reflectivity. The magnetron sputter deposited multilayers have been calibrated and characterized using Cu K α grazing incidence X-ray reflectometry. Reflectivity measured at near-normal incidence on a synchrotron radiation source reaches 12% with a full width at half maximum of nearly 40 eV. Experimental results are compared with theoretical simulation using available optical constants for Mo, Si and B4C in this spectral range.