MULTILAYER X-RAY MIRRORS - INTERFACIAL ROUGHNESS, SCATTERING, AND IMAGE QUALITY

Scattering of the multilayer coatings used for our normal incidence so ft x-ray telescope at lambda = 63.5 angstrom has been measured at lamb da = 1.54 angstrom and grazing angles of incidence and at soft x rays near normal incidence. Furthermore, the edge of the moo is used as a k nown test target to estimate the amount of scattering in the arcsec ra nge from images obtained on the date of the solar eclipse on July 11, 1991. The internal surfaces of the coating -are inspected by high-reso lution electron microscopy. A theoretical model describing the evoluti on and replication of roughness from layer to layer throughout the str ucture, which is in agreement with all experimental data is presented. We find that practically all roughness caused by the growth of the mu ltilayer structure occurs at spatial frequencies which are too high to produce scattering. The substrate roughness is replicated at lower sp atial frequencies which might produce scattering within the field of v iew of an instrument. However, roughness in this range is below the 0. 5 angstrom level again resulting in insignificant amounts of scatter.