Optical constants in the hard X-ray/soft gamma ray range of selected materials for multilayer reflectors

Abstract

Future Astrophysics missions operating in the hard X-ray/Soft Gamma ray range is slated to carry novel focusing telescopes based on the use of depth graded multilayer reflectors. Current design studies show that, at the foreseen focal lengths, it should be feasible to focus X-rays at energies as high as 300 keV. These designs use extrapolations of theoretical and experimentally determined optical constants from below 200 keV. In this paper we report on the first experimental determination of optical constants up to and above 200 keV. We present these first results as obtained at the National Synchrotron Light Source in Brookhaven and compare these to results obtained previously up to 180 keV of some of the same materials at the European Synchrotron Radiation Facility in Grenoble.

Stacked depth graded multilayer for hard X-rays measured up to 130 keV

“…This will be referred to as Windt-modified. It can be seen in figure 3 that using Windt-modified gives overall a better fit to the data than Jensen et al 16 but as seen clearly from figure 3b the fit predicts a factor of 2 lower reflectivity at some angles, whereas using the theoretical optical constants the fit is as good as can be expected from this type of measurements. This indicates that the extinction coefficient in Windt-modified is likely not correct since there is good agreement between the measured refractive index and the theoretical values.…”

“…However, for the extinction coefficient, k, there are clear differences. The extinction coefficient value measured by Jensen et al 16 was too high, see reference 16, and can not fit the data since they introduce too much absorption, see figure 3.…”

“…Also Jensen et al 16 have measured the optical constants between 50 keV and 150 keV for Ni 0.93 V 0.07 , SiC, and WC. There is very good agreement between the theoretically calculated refractive index, n, and both sets of measurements.…”

“…Over the W absorption edge at 69.5 keV and up to 100 keV there is a linear dependency of the extinction coefficient, k, between W and WC using the theoretical values. By taking this linear dependency and multiply onto the extinction coefficient for W measured by Windt et al 15 and combine that with the refractive index from Jensen et al 16 we get the best estimate of a set of measured optical constants for WC. Figure 3 shows a fit using the optical constants from Windt et al 15 for Ni 0.93 V 0.07 and SiC combined with the scaled optical constant for WC.…”

“…The refractive index, n, measured for WC made by Jensen et al 16 has a good agreement with the refractive index from the theoretical values so this has been used. Over the W absorption edge at 69.5 keV and up to 100 keV there is a linear dependency of the extinction coefficient, k, between W and WC using the theoretical values.…”