Low Mechanical Loss TiO₂:GeO₂ Coatings for Reduced Thermal Noise in Gravitational Wave Interferometers
The sensitivity of current and planned gravitational wave interferometric detectors is limited, in the most critical frequency region around 100 Hz, by a combination of quantum noise and thermal noise. The latter is dominated by Brownian noise: thermal motion originating from the elastic energy dissipation in the dielectric coatings used in the interferometer mirrors. The energy dissipation is a material property characterized by the mechanical loss angle. We have identified mixtures of titanium dioxide (TiO₂) and germanium dioxide (GeO₂) that show internal dissipations at a level of 1 × 10⁻⁴, low enough to provide improvement of almost a factor of 2 on the level of Brownian noise with respect to the state-of-the-art materials. We show that by using a mixture of 44% TiO₂ and 56% GeO₂ in the high refractive index layers of the interferometer mirrors, it would be possible to achieve a thermal noise level in line with the design requirements. These results are a crucial step forward to produce the mirrors needed to meet the thermal noise requirements for the planned upgrades of the Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) and Virgo detectors.
© 2021 American Physical Society. (Received 26 March 2021; revised 23 June 2021; accepted 14 July 2021; published 10 August 2021) This Letter is supported by the National Science Foundation (NSF) LIGO program through Grants No. 1710957 and No. 1708010. We also acknowledge the support of the LSC Center for Coatings Research, jointly funded by the NSF and the Gordon and Betty Moore Foundation (GBMF). K. P., A. M., R. B. and M. M. F. are grateful for support through NSF Grants No. PHY-1707866, No. PHY-1708175, No. PHY-2011571, and No. PHY-2011706, and GBMF Grant No. 6793. The work carried out at U. Montreal benefited from the support of the NSERC, the CFI, and the FRQNT through the RQMP.
Published - PhysRevLett.127.071101.pdf
Accepted Version - 2108.04954.pdf
Supplemental Material - supplemental_material.pdf