Assessment Of Surface Topography By X-Ray Scattering Measurements

In the context of developing optics for X-ray astronomy, measurements of a variety of flat mirrors and telescopes have revealed that the total integrated scatter (TIS) formalism, well known in the optical regime, also describes the surface scattering of soft X-rays. The topography of mirror surfaces can be well studied by angle resolved X-ray scattering, from which e.g. the power spectrum and auto-covariance function of surface irregularities can be inferred. X-rays can also be used as diagnostic tool to identify surface slope changes and periodic like structures. A quantitative formalism is derived to separate the spectrum of spatial surface wavelengths into components which can be treated in a geometrical optics appraoch and those which need exact diffraction treatment. This formalism has been applied to predict the X-ray point spread function of telescopes from mechanical profile measurements. The agreement between prediction and X-ray measurement is remarkably good.