The High-Energy X-ray Probe (HEX-P) is a probe-class next-generation high-energy X-ray mission concept that will vastly extend the reach of broadband X-ray observations. Studying the 2-200 keV energy range, HEX-P has 40 times the sensitivity of any previous mission in the 10-80 keV band, and will be the first focusing instrument in the 80-200 keV band. A successor to the Nuclear Spectroscopic Telescope Array (NuSTAR), a NASA Small Explorer launched in 2012, HEX-P addresses key NASA science objectives, and will serve as an important complement to ESA's L-class Athena mission. HEX-P will utilize multilayer coated X-ray optics, and in this paper we present the details of the optical design, and discuss the multilayer prescriptions necessary for the reflection of hard X-ray photons. We consider multiple module designs with the aim of investigating the tradeoff between high-and low-energy effective area, and review the technology development necessary to reach that goal within the next decade.

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We are developing depth-graded, multilayer-coated mirrors for astrophysical hard X-ray focusing telescopes. In this paper, we discuss the primary technical challenges associated with the multilayer coatings, and report on progress to date. We h a v e sputtered constant d-spacing and depth-graded W Si multilayers onto 0.3 0.5 mm thick DURAN glass AF45 and D263 and 0.4 mm thick epoxy replicated aluminum foils ERAFs, both of which are potential mirror substrates. We have characterized the interfacial roughness, uniformity, and stress of the coatings. The average interfacial roughness of each multilayer was measured from specular re ectivity scans i = r using Cu K X-rays. The thin lm stress was calculated from the change in curvature induced by the coating on at glass substrates. Thickness and roughness uniformity w ere measured by taking specular re ectivity scans of a multilayer deposited on the inside surface of a quarter cylinder section.We found that interfacial roughness in the multilayers was typically between 3.5 and 4.0 A on DESAG glass, and between 4.5 and 5.0 A on the ERAFs. Also, we found that coatings deposited on glass that has been thermally formed into a cylindrical shape performed as well as at glass. The lm stress, calculated from Stoney's equation, for a 200 layer graded multilayer was approximately 200 MPa. Our uniformity measurements show that with no ba es to alter the deposition pro le on a curved optic, the layer thickness di ers by 20 between the center and the edge of the optic. Interfacial roughness, however, remained constant, around 3.6 A, throughout the curved piece, even as the layer spacing dropped o .

ABSTACTThe deposition and X-ray performance of multilayer structures with d-spacings ranging from 1 .2nm to 3 .5nm has been presented. Different pairs of materials such as W (Mo, Ni, Cr, and La)/B4C, Ni (Cr, Co, V)/C have been considered. Xray reflectivity ofthe multilayers has been measured in the photon energy range from O. l8keV to -400keV. W/B4C structures with d-4.25nm showed reflectivity greater than 30% at Cu-K a (E8keV). Performance of a W/B4C structure with dl.5nm has been compared with TIAP crystal performance in analysis of SKa (l.74keV), AlKa (1 .5keV), Mg-Ka (1 .25keV) and Na-Ka (1 .O4keV) radiation. Results showed that small d-spacing multilayers can be considered for TIAP crystal replacement in Wavelength Dispersive X-Ray Fluorescence (WDXRF) spectrometers.The absolute reflectivity of near normal incidence structures at OKa (293eV), CKa ('277eV) and BKa (1 83eV) radiation lines has been measured to be 1.5%, 14% and 43% respectively with spectral resolution ofup to O.6%.