ANGULAR RESOLVED SOFT-X-RAY SCATTERING FROM OPTICAL-SURFACES

We present angular resolved scattering (ARS) distributions of various glass mirrors and of SiC mirrors at glancing incidence. The measurements have been performed at the XUV reflectometer station at the DORIS2 storage ring (HASYLAB) between 25 and 1.2 nm wavelength. The data are compared with different scattering theories by using least squares fitting procedures. Of all the available theories the Rayleigh-Rice vector perturbation theory is based on the most realistic model and gives by far the best agreement between experiment and theory. Indeed, even near the critical angle, where anomalous scattering arises, excellent agreement was obtained. Also, convincing evidence for scattering from dielectric fluctuations inside some of the glass samples was found. The rms-roughness, autocorrelation length (measure of the mean lateral separation of the surface irregularities), and the type of correlation function could be determined. Furthermore, we show that ARS-measurements are sensitive to detect irregularities with a mean lateral separation from 50 to 1500 nm. Therefore ARS-measurements in the soft X-ray range could become an important tool to supplement other methods characterizing optical surfaces. Practically all other familiar methods are restricted in spatial frequency corresponding to a lateral resolution above a few microns. © 1990 IOP Publishing Ltd.