Low mechanical loss TiO${}_2$:GeO${}_2$ coatings for reduced thermal noise in Gravitational Wave Interferometers

Abstract

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 (TiO${}_2$) and germanium dioxide (GeO${}_2$) that show internal dissipations at a level of 1 $\times 10^{-4}$, low enough to provide almost a factor of two improvement on the level of Brownian noise with respect to the state-of-the-art materials. We show that by using a mixture of 44% TiO${}_2$ and 56% GeO${}_2$ 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 and Virgo detectors.

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• Effects of mixing and annealing on the optical and mechanical properties of TiO${}_2$:Ta${}_2$O${}_5$ amorphous coatings
• Development of ion-beam sputtered silicon nitride thin films for low-noise mirror coatings of gravitational-wave detectors
• Sensors and Actuators for the Advanced LIGO+ Upgrade
• Imaging Scatterometer for Observing In-Situ Changes to Optical Coatings During Air Annealing
• Determination of compressive stress in thin films using micro-machined buckled membranes
• Optimizing Gravitational-Wave Detector Design for Squeezed Light
• Mirror Coating Thermal Noise Mitigation Using Multi-Spatial Mode Cavity Readout
• Mechanical loss and stability analysis of NEXCERA in ultra-stable optical cavities
• Characterization of ion-beam-sputtered AlF${}_3$ thin films for gravitational-wave interferometers
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• A Systematic Error in the Internal Friction Measurement of Coatings for Gravitational Waves Detectors
• Thermal Deformation Reduction in High-Power Interferometry with Higher-Order Laser Modes
• Thermal Noise Reduction in Ternary Optical Coatings: From Ti::GeO${}_2$-Based Ternary Systems to High Index Materials
• Connected Network Model for the Mechanical Loss of Amorphous Materials