Development of grazing incidence multilayer mirrors for hard X-ray focusing telescopes

Peter H. Mao, Fiona A. Harrison, Yuriy Y. Platonov, David Broadway, Brian DeGroot, Finn Erland Christensen, William W. Craig, Charles J. Hailey

Research output: Contribution to journalConference articleResearchpeer-review

Abstract

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 have 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 reflectivity scans (θi = θr) using Cu Kα X-rays. The thin film stress was calculated from the change in curvature induced by the coating on flat glass substrates. Thickness and roughness uniformity were measured by taking specular reflectivity scans of a multilayer deposited on the inside surface of a quarter cylinder section. We found that interfacial roughness (σ) in the multilayers was typically between 3.5 and 4.0 Å on DESAG glass, and between 4.5 and 5.0 Å on the ERAFs. Also, we found that coatings deposited on glass that has been thermally formed into a cylindrical shape performed as well as flat glass. The film stress, calculated from Stoney's equation, for a 200 layer graded multilayer was approximately 200 MPa. Our uniformity measurements show that with no baffles to alter the deposition profile on a curved optic, the layer thickness differs by ~20% between the center and the edge of the optic. Interfacial roughness, however, remained constant, around 3.6 Å, throughout the curved piece, even as the layer spacing dropped off.
Original languageEnglish
JournalProceedings of SPIE, the International Society for Optical Engineering
Volume3114
Pages (from-to)526-534
ISSN0277-786X
DOIs
Publication statusPublished - 1997
EventEUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy VIII - San Diego, CA., United States
Duration: 27 Jul 199727 Jul 1997

Conference

ConferenceEUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy VIII
CountryUnited States
CitySan Diego, CA.
Period27/07/199727/07/1997

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