Speaker
Description
The thermal noise of the end-test-mass mirrors in gravitational-wave detectors remains a major sensitivity limitation, largely due to the multi-layer Bragg-mirror-stacks required to achieve ultra-high reflectance. For the next-generation Einstein Telescope (ET), we propose a stacked-mirror approach that combines the complementary advantages of metasurfaces and Bragg mirrors, while mitigating their individual drawbacks. Our design integrates a super-polished silicon substrate coated with a Bragg-mirror-stack, an anti-resonant Fabry–Pérot spacer, and a structured amorphous-silicon metasurface layer on top.
While silicon is the target substrate foe ET mirrors, as a first experimental step, we are fabricating fused-silica test wafers with amorphous-silicon metasurfaces to assess robustness against fabrication-induced uncertainties. Reflection measurements will benchmark optical performance (reflectivity and noise), while numerical simulations based on rigorous coupled-wave analysis (RCWA), finite-element method (FEM), and finite-difference time-domain (FDTD) methods are used to predict fabrication tolerances and thermal-noise behavior in advance.
This hybrid concept offers for relevant substrate sizes a promising technology pathway toward mirrors with simultaneously extremely high reflectance and reduced thermal noise, paving the way for improved performance of ET end-test masses.
