Speaker
Description
Coating thermal noise limits the sensitivity of gravitational-wave detectors in the most sensitive frequency band. As third-generation detectors, like the Einstein Telescope or LIGO Voyager, advance toward cryogenic interferometers to reduce thermal noise, current coating materials such as Ta$_{2}$O$_{5}$ and SiO$_{2}$ become inadequate due to their high mechanical loss at low temperatures. Alternative materials, like a-Si and SiN$_{x}$, are promising due to low thermal noise, but the high optical absorption of a-Si is a limiting factor.
We propose a paradigm-shifting approach: forming highly reflective structures directly inside the crystalline silicon mirror substrates via ion implantation. The main aim is the creation of low refractive index layers between crystalline silicon layers formed by the substrate itself, preserving the excellent optical properties, such as low absorption, of crystalline silicon compared to aSi.
Using a dedicated ion implanter, we created buried SiO$_{2}$ and SiN$_{x}$ layers at controlled depths inside c-Si substrates. We report the first successful fabrication of a multilayer structure in the context of mirrors for gravitational-wave detectors. Simulations of the implantation schedule are compared with Rutherford Backscattering Spectrometry (RBS) and ellipsometry measurements, confirming the depth and uniformity of the implanted layers. Furthermore, preliminary optical analysis and mechanical loss results are presented. Ongoing development of SiN$_{x}$-implanted structures may be a way to meet the strict requirements of third-generation observatories.