Mirror coating solution for the cryogenic Einstein telescope

Kieran Craig, Jessica Steinlechner, Peter G. Murray, Angus S. Bell, Ross Birney, Karen Haughian, Jim Hough, Ian MacLaren, Steve Penn, Stuart Reid, Raymond Robie, Sheila Rowan, Iain W. Martin

Research output: Contribution to journalArticlepeer-review

23 Citations (Scopus)
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Planned cryogenic gravitational-wave detectors will require improved coatings with a strain thermal noise reduced by a factor of 25 compared to Advanced LIGO. We present investigations of HfO2 doped with SiO2 as a new coating material for future detectors. Our measurements show an extinction coefficient of k=6×10-6 and a mechanical loss of φ=3.8×10-4 at 10 K, which is a factor of 2 below that of SiO2, the currently used low refractive-index coating material. These properties make HfO2 doped with SiO2 ideally suited as a low-index partner material for use with a-Si in the lower part of a multimaterial coating. Based on these results, we present a multimaterial coating design which, for the first time, can simultaneously meet the strict requirements on optical absorption and thermal noise of the cryogenic Einstein Telescope.

Original languageEnglish
Article number231102
Number of pages6
JournalPhysical Review Letters
Issue number23
Publication statusPublished - 13 Jun 2019


  • Einstein telescope
  • cryogenic temperatures
  • gravitational waves


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