Soft X-ray Scattering by Optical Surfaces

D esign of grazing incidence soft x-ray telescope mirrors requires information regarding performance of optical surfaces in the wavelength region of interest. A method is described for measuring x-ray scattering in the reflected beam to sec of arc accuracy. Measurements of nine metal and three glass optical flat samples were made. The glass samples were superior at 8.34 A, but both types performed almost equally well at 44 A The scattering was found to be large in magnitude at small glancing angles of incidence. The scattering then decreased with increasing glancing angle of incidence until a critical angle was passed. At larger angles the scattering increased again. In general, all samples scattered more at 44 Athan at 8.34A. The data indicate that grazing incidence soft x-ray telescope mirrors should be designed by choosing the appropriate angle of incidence to minimize x-ray scattering in the wavelength band of interest.