Mapping the optical absorption of a substrate-transferred crystalline AlGaAs coating at 1.5 mu m

J. Steinlechner, I.W. Martin*, A. Bell, G. Cole, J. Hough, S. Penn, S. Rowan, S. Steinlechner

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


The sensitivity of second and third generations of interferometric gravitational wave (GW) detectors will be limited by the thermal noise of the test-mass mirrors and highly reflective coatings. Recently developed crystalline coatings show a promising thermal noise reduction compared to presently used amorphous coatings. However, stringent requirements apply to the optical properties of the coatings as well. We have mapped the optical absorption of a crystalline AlGaAs coating that is optimized for high reflectivity for a wavelength of 1064 nm. The absorption was measured at 1530 nm, where the coating stack transmits approximately 70% of the laser light. The measured absorption was lower than (30.2 +/- 11.1) ppm, which is equivalent to (3.6 +/- 1.3) ppm for a coating stack that is highly reflective at 1530 nm. While this is a very promising low absorption result for alternative low-loss coating materials, further work will be necessary to reach the requirements of < 1 ppm for future GW detectors.
Original languageEnglish
Article number105008
Number of pages12
JournalClassical and Quantum Gravity
Issue number10
Publication statusPublished - 21 May 2015
Externally publishedYes


  • gravitational wave detectors
  • absorption
  • crystalline coating

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