X-ray characterization of thin foil gold mirrors of a soft X-ray telescope for ASTROSAT

Abstract

X-ray reflectivity measurements were performed on several thin foil gold mirrors fabricated in TIFR for a Soft X-ray Imaging Telescope. The mirrors were made from thin aluminum foils with a reflecting layer of sputtered gold transferred from a smooth glass mandrel using an epoxy. X-ray reflectivity measurements were performed on a sample of randomly selected mirrors using CuK α (8.05 keV), CrK α (5.41 keV) X-rays and also at several energies in the energy range of 155-300 eV using the synchrotron source Indus-1. It was found that the roughness of the low-density top gold layer as obtained from the fitting of X-ray reflectivity data for CuK α radiation is relatively more as compared to that obtained from the CrK α radiation. This indicates that in the mirrors made by this process, the upper surfaces are smoother as compared to the deeper layers. It was also observed that the critical angle almost vanishes in the very low energy range of 290-300 eV due to strong absorption effects of the low density material sitting on top of these mirrors. Due to this absorption effect, efficiency of these mirrors reduces in this energy range. This is first time that reflectivity measurements are being reported for very soft X-rays (≤ 300 eV) for mirrors made for any X-ray astronomy mission.

Soft X-ray Focusing Telescope Aboard AstroSat: Design, Characteristics and Performance

“…The mirrors were tested and evaluated extensively using X-ray reflectivity measurements as described in Sagdeo et al (2010). The mirrors showed roughness of ∼7-10 Å.…”

Astrosat: Some Key Science Prospects

“…The SXT is an imaging X-ray instrument with a grazing incidence X-ray telescope made with two sets of conical foil mirrors. 5 At the focal plane is a CCD camera that has an energy resolution of about 200-250 eV at 6.4 keV while the telescope has an angular resolution in the range of 3-4 arcmin and field of view of 41 arcmin. As a supporting instrument, the SXT broadens the energy range of the X-ray instruments of ASTROSAT at the lower end to about 0.35 keV.…”

Grazing incidence optics for X-ray astronomy

“…The modeling leads to the surface roughness parameter which indicates the quality of the surface and its scattering properties. One such set of measurements were carried out by us for X-ray mirrors developed in TIFR and are described in [15]. The surface roughness expressed in terms of scale heights of irregularities was determined to be 10 Angstroms for SXT, comparable to the mir- Examples of X-ray telescopes and X-ray images of the universe Figures 8,9,10 and 11 show three examples of Xray telescopes, viz., Chandra X-ray Observatory with four nested mirrors and 10 m focal length, XMM-Newton telescope with 58 nested mirrors and 8 m focal length, and a Soft X-ray Telescope (SXT) with 40 nested shells and 2 m focal length for India's first Astronomy satellite, ASTROSAT to be launched in 2012.…”