A stacked prism lens concept for next-generation hard X-ray telescopes

Abstract

Effective collecting area, angular resolution, field of view and energy response are fundamental attributes of X-ray telescopes. The performance of state-of-the-art telescopes is currently restricted by Wolter optics, especially for hard X-rays. In this paper, we report the development of a new approach -the Stacked Prism Lens, which is lightweight, modular and has the potential for a significant improvement in effective area, while retaining high angular resolution. The proposed optics is built by stacking discs embedded with prismatic rings, created with photoresist by focused UV lithography. We demonstrate the SPL approach using a prototype lens which was manufactured and characterized at a synchrotron radiation facility. The design of a potential satellite-borne X-ray telescope is outlined and the performance is compared to contemporary missions.Since the first orbiting X-ray telescope, the Einstein Observatory, was launched in 1978, focusing X-ray telescopes (XRTs) have provided new knowledge on the universe by observing remote objects in the X-ray spectrum 1, 2 . The performance of XRTs is mainly determined by the optics. State-of-the-art focusing XRTs rely on Wolter optics, for which X-rays that are nearly parallel to the nested mirrors are collected by total external reflection. This has been successfully employed in several telescopes (e.g. Chandra 3 , XMM-Newton 4 , Swift 5 and the planned ATHENA mission 6 ), for X-rays in the energy range of 0.1 to 10 keV with high values of efficiency, angular resolution and sensitivity. However, for X-ray energies higher than 10 keV, using the same technique compromises spatial resolution and efficiency since the grazing angle quickly decreases with energy, making the focal length of the system impractically long and the field of view (FoV) very small. Moreover, the efficiency of the mirrors decreases, and nesting becomes more difficult. To mitigate this issue, it is possible to use multi-layered coatings and Bragg-reflection from depthgraded multi-layers to increase the grazing angle in the hard X-ray energy range 7, 8 . Current hard X-ray focusing telescopes such as NuSTAR 9 and Astro-H 10, 11 are designed this way. Although this provides a significant improvement in performance for hard X-rays, the long focal length is challenging when designing missions, and the small effective collecting area and narrow FoV limits the scientific return from missions. In addition, the angular resolution is severely influenced by 1 arXiv:2002.02299v1 [astro-ph.IM] 6 Feb 2020 figure error, surface roughness and assembly precision 2 .At present, refractive 12, 13 and diffractive transmissive X-ray optics 14 have been used in a wide range of applications [15][16][17] , such as biology 18 , chemistry 19 and lithography 20,21 . Several novel zone plates 14 , such as multilayer zone plates 22-25 , interlaced zone plates 26 and stacked zone plates 27 , as well as refractive optics, such as commercially available compound refractive X-ray lenses 13 , have been developed for hard X-ray ima...

Hard X-ray Polarimetry -- An overview of the method, science drivers and recent findings

“…Unavailability of focusing optics in >80 keV warrants a large area detector plane to be the obvious solution to build a sensitive polarimeter. Emergence of Laue lens based on diffraction in crystals allowing concentration of X-rays above 100 keV (Barrière et al, 2011) or the newly proposed Stacked Prism Lenses (SPL, Mi et al, 2019) will provide an excellent solution in future to develop sensitive detectors in the sub-MeV region (Roques et al, 2012). However, in absence of any real implementation of these techniques at present, an effective approach might be to use a large area detector in wide FOV configuration.…”

Achromatic X-ray lenses based on low-Z hydride compounds

“…= tan(α 0 ) would correspond to α 0 80.5 • . Hence, the idea that underlies CRLs is applied to the convex shape of the refractive component, [18][19][20] as shown in Fig. 5.…”

Gamma-Ray Polarimetry

“…Development of focusing optics like the Laue lens (Barrière et al, 2011) or newly proposed stacked prism lenses (Mi et al, 2019) and channelling optics (Shirazi et al, 2018) to concentrate photons above 100 keV have the potential to significantly increase the sensitivity of γ-ray polarimeters.…”