Abstract
Gravitational waves are detected by measuring length changes between mirrors in the arms of kilometre-long Michelson interferometers. Brownian thermal noise arising from thermal vibrations of the mirrors can limit the sensitivity to distance changes between the mirrors, and, therefore, the ability to measure gravitational-wave signals. Thermal noise arising from the highly reflective mirror coatings will limit the sensitivity both of current detectors (when they reach design performance) and of planned future detectors. Therefore, the development of coatings with low thermal noise, which at the same time meet strict optical requirements, is of great importance. This article gives an overview of the current status of coatings and of the different approaches for coating improvement.This article is part of a discussion meeting issue 'The promises of gravitational-wave astronomy'.
Highlights
Since 2015 several gravitational-wave signals have been detected by the Advanced LIGO1 and Advanced Virgo gravitational-wave detectors [1,2,3,4,5].Gravitational waves cause extremely small distance changes—so small that typical gravitational waves2018 The Authors
Detailed investigations of SiN deposited via plasma-enhanced chemical vapour deposition (PECVD) have shown that the exact material composition has a strong effect on the material properties, e.g. on the optical absorption, the refractive index and the mechanical loss [47], with evidence of lower mechanical losses than current GW-coating materials at room temperature and at low temperature down to 10 K [48,49]
— The blue line shows the thermal noise performance of the coatings made of SiO2 and Ti:Ta2O5 currently used in Advanced LIGO1 (aLIGO) at room temperature, on a SiO2 substrate and for the currently used beam radius of 6 cm
Summary
Gravitational waves are detected by measuring length changes between mirrors in the arms of kilometrelong Michelson interferometers. Brownian thermal noise arising from thermal vibrations of the mirrors can limit the sensitivity to distance changes between the mirrors, and, the ability to measure gravitational-wave signals. Thermal noise arising from the highly reflective mirror coatings will limit the sensitivity both of current detectors (when they reach design performance) and of planned future detectors. The development of coatings with low thermal noise, which at the same time meet strict optical requirements, is of great importance. This article gives an overview of the current status of coatings and of the different approaches for coating improvement. This article is part of a discussion meeting issue ‘The promises of gravitational-wave astronomy’
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