X-ray Scatter Measurements from Thermally Slumped Thin Glass Substrates for the HEFT Hard X-ray Telescopes

Ahsen M. Hussain Finn E. Christensen 
Danish Space Research Institute, Juliane Maries Vej 30,
Copenhagen Dk-2100, Denmark.

Mario A. Jimenez-Garate, William W. Craig, Charles J. Hailey, Todd R. Decker, Marcela Stern,
Columbia Astrophysics Laboratory, Columbia University, New York, USA.

David L. Windt,
Bell Laboratories, Lucent Technologies, New Jersey, USA.

Peter H. Mao, Fiona A. Harrison,
Space Radiation Laboratory, California Institute of Technology, Pasadena, California, USA.

Giovanni Pareschi,
Osservatorio Astronomico di Brera-Milano, Merate, Italy.

Manuel Sanchez del Rio, Alexei Souvorov, Andreas K. Freund, Remi Tucoulou,
European Synchrotron Radiation Facility (ESRF), Grenoble, France.

Anders Madsen, Christian Mammen,
Oersted Laboratory, University of Copenhagen, Copenhagen, Denmark.



ABSTRACT

We have performed X-ray specular re ectivity and scattering measurements of thermally slumped glass substrates
on X-ray diffractometers utilizing a rotating anode X-ray source (8.048 keV) at the Danish Space Research Institute
(DSRI) and synchrotron radiation (18 & 28keV) at the European Synchrotron Radiation Facility (ESRF) optics
Bending Magnet (BM05) beamline. In addition, we tested depth graded W/Si multilayer-coated slumped glass using
X-ray specular re ectivity measurements at 8.048 keV (DSRI) & 28 keV (ESRF) and energy-dispersive measurements
in the 20{50 keV range at a double-axis diffractometer at the Oersted Laboratory, University of Copenhagen. The
thermally slumped glass substrates will be used to fabricate the hard X-ray grazing incidence optics for the High-
Energy Focusing Telescope (HEFT) 7,8. We compared the measurements to the SODART-mirrors 1 from the SRG 17
telescope mission program. The surface scatter measurements of the thermally slumped glass substrates yields
Half Power Diameters (HPD's) of single-bounce mirrors of full-illuminated lengths of . 40 arcseconds for typical
substrates and as low as. 10 arcseconds for the best substrates, whereas the SODART mirrors yields HPD's of . 80
arcseconds with very little variation. Both free-standing glass substrates and prototype mounted and multilayer-
coated optics were tested. The results demonstrate that the surface scatter contribution, plus any contribution from
the mounting procedure, to the Half Power Diameter (HPD) from a telescope using the slumped glass optics will be
in the subarcminute range. In addition we measured low surface microroughness, yielding high re ectivity, from the
glass substrates (~ 2  A), as well as from the depth graded W/Si multilayer-coated glass (interfacial width . 4.2  A).
Keywords: X-ray Re ectivity, X-ray Scattering, Synchrotron Radiation, Hard X-ray Telescopes, X-ray Optics,
Segmented Optics, Wolter-I Optics, Thermal Slumping, Depth Graded Multilayers.