X-ray characterization of thin foil gold mirrors of a soft X-ray telescope for ASTROSAT
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.
KeywordsX-ray telescope: ASTROSAT X-ray mirrors: reflectivity
We are indebted to Mr. V. M. Risbud, Ganesh Gawde of TIFR and Dr. V. R. Rana (now at CalTech) for extensive help in the fabrication of X-ray mirrors and the test samples used here. We thank Dr. Y. Tawara, Dr. H. Kunieda and Dr. Y. Ogaska of the University of Nagoya for help with the replication technique used for making the mirrors. We thank Mr. A. T. Kothare, Dr. K. Mukerjee, Mr. D. Pathare, Mr. I. Mirza of TIFR who helped design the epoxy spray system, built and maintained by Mr. V. M. Risbud and G. Gawade. We thank Dr. N. J. Westergaard of the Danish Space Research Centre for for helping with the design of the telescope. Thanks are also due to Mr. Atul Nagras and Mr. S. Gokhale of Advanced Process Technology, Pune, for providing unstinted help in the fabrication and maintenance of the DC magnetron sputtering system for gold coating.
- 11.Rana, V.R. et al.: X-ray optics: A new technology development for ASTROSAT and future scientific space missions. In: Proceedings of Satellite Technology Day, 19 April 2005, ISAC, Bangalore (2005)Google Scholar
- 12.Yadav, N., Singh, K.P.: TIFR Technical Report. Mirror fabrication for soft X-ray telescope (ASTROSAT): AST-SXT-TFR-TEC-PID (2007)Google Scholar
- 14.Born, M., Wolf, E.: In: Principles of Optics, Chapter 1, p. 35, 6th edn. Pergamon Press, New York (1980)Google Scholar
- 16.Nevot, L., Croce, P.: Caracterisation des surfaces par reflexion rasante de rayons X. Application a l‘etude du polissage de quelques verres. Rev. Phys. Appl. 15, 761 (1980)Google Scholar