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Published December 22, 2023 | Published
Journal Article Open

Hydrogen-Induced Ultralow Optical Absorption and Mechanical Loss in Amorphous Silicon for Gravitational-Wave Detectors


The sensitivity of gravitational-wave detectors is limited by the mechanical loss associated with the amorphous coatings of the detectors' mirrors. Amorphous silicon has higher refraction index and lower mechanical loss than current high-index coatings, but its optical absorption at the wavelength used for the detectors is at present large. The addition of hydrogen to the amorphous silicon network reduces both optical absorption and mechanical loss for films prepared under a range of conditions at all measured wavelengths and temperatures, with a particularly large effect on films grown at room temperature. The uptake of hydrogen is greatest in the films grown at room temperature, but still below 1.5 at.% H, which show an ultralow optical absorption (below 10 ppm) measured at 2000 nm for 500-nm-thick films. These results show that hydrogenation is a promising strategy to reduce both optical absorption and mechanical loss in amorphous silicon, and may enable fabrication of mirror coatings for gravitational-wave detectors with improved sensitivity.

Copyright and License

© 2023 American Physical Society.


We would like to thank C. S. Menoni and A. Davenport for the refractive index measurements, and R. X. Adhikari and F. Salces-Carcoba for useful discussions on the noise estimates for Voyager. We gratefully acknowledge the support of the LIGO Scientific Collaboration and Center for Coatings Research, jointly funded by the NSF and the Gordon and Betty Moore Foundation through Grant No. 6793. The UCB portion of this work was supported through NSF Grant No. PHY-2011719, the SU portion of this work was supported through NSF Grants No. PHY-2011571 and No. PHY-2011706, and the Caltech portion of this work was supported through NSF Grants No. PHY-0823459 and No. PHY-1764464. Work performed at NRL was supported by the Office of Naval Research.


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Additional details

December 22, 2023
December 22, 2023