Astronomical soft x-ray mirrors reflectivity enhancement by multilayer coatings with carbon overcoating
Pareschi, Giovanni ; Cotroneo, Vincenzo ; Spiga, Daniele ; ...Negri, Barbara
Oct - 2004
DOI: 10.1117/12.556838
Event Title :
Published in:
Publisher:
type: Conference Proceedings
Abstract
A number of X-ray astronomical missions of near future will make use of hard X-ray optics with broad-band multilayer coatings. However multilayer mirrors can be also useful to enhance the effective area of a given X-ray telescope in the classical low energy X-ray band (0.1 - 10 keV), the window where X-ray spectroscopy provides very useful plasma diagnostics) with a consistent gain with respect to usual single-layer reflectors. Multilayers for soft X-rays are based on stacks with constant d-spacing (in order to minimize the loss due to the photoelectric effect). A further gain in reflectivity (however only restricted to the energy range between 0.5 and 4 keV) can be achieved by using a low density material as a first external layer of the film, with the role of reducing the photoelectric absorption effect when the mirror acts in total external reflection regime (Carbon is the most performing material for this specific scope). In this paper the impact of using soft X-ray multilayer mirrors in future X-ray telescopes is discussed, and soft X-ray reflectivity tests performed on prototype samples presented.
keywords : Absorption,Carbon,Hard x-rays,Mirrors,Multilayers,Optical coatings,Optics,Photoelectric effect,Plasma diagnostics,Reflection,Reflectivity,Reflectors,Spectroscopy,X-ray telescopes,X-rays