Methods for reducing singly reflected rays on the Wolter-I focusing mirrors of the FOXSI rocket experiment

Juan Camilo Buitrago-Casas, Ronald Elsner, Lindsay Glesener, Steven Christe, Brian Ramsey, Sasha Courtade, Shin Nosuke Ishikawa, Noriyuki Narukage, Paul Turin, Juliana Vievering, P. S. Athiray, Sophie Musset, Säm Krucker

Research output: Chapter in Book/Report/Conference proceedingConference contribution

5 Scopus citations


In high energy solar astrophysics, imaging hard X-rays by direct focusing offers higher dynamic range and greater sensitivity compared to past techniques that used indirect imaging. The Focusing Optics X-ray Solar Imager (FOXSI) is a sounding rocket payload that uses seven sets of nested Wolter-I figured mirrors together with seven high-sensitivity semiconductor detectors to observe the Sun in hard X-rays through direct focusing. The FOXSI rocket has successfully flown twice and is funded to fly a third time in summer 2018. The Wolter-I geometry consists of two consecutive mirrors, one paraboloid and one hyperboloid, that reflect photons at grazing angles. Correctly focused X-rays reflect once per mirror segment. For extended sources, like the Sun, off-axis photons at certain incident angles can reflect on only one mirror and still reach the focal plane, generating a background pattern of singly reflected rays (i.e., ghost rays) that can limit the sensitivity of the observation to faint, focused sources. Understanding and mitigating the impact of the singly reflected rays on the FOXSI optical modules will maximize the instruments' sensitivity to background-limited sources. We present an analysis of the FOXSI singly reflected rays based on ray-tracing simulations and laboratory measurements, as well as the effectiveness of different physical strategies to reduce them.

Original languageEnglish (US)
Title of host publicationOptics for EUV, X-Ray, and Gamma-Ray Astronomy VIII
EditorsStephen L. O'Dell, Giovanni Pareschi
ISBN (Electronic)9781510612556
StatePublished - 2017
EventOptics for EUV, X-Ray, and Gamma-Ray Astronomy VIII 2017 - San Diego, United States
Duration: Aug 8 2017Aug 10 2017

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceOptics for EUV, X-Ray, and Gamma-Ray Astronomy VIII 2017
Country/TerritoryUnited States
CitySan Diego

Bibliographical note

Publisher Copyright:
© 2017 SPIE.


  • OXSI
  • Wolter-I optics
  • X-ray telescope
  • solar


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