Interference coatings for gravitational wave interferometers
Thermal noise is a fundamental limitation in optical interferometry experiments as thermally driven fluctuations cause variations in the optical path. In particular, the sensitivity of gravitational wave detectors, such as Advanced LIGO and Advanced Virgo, is affected by the thermal noise in the high-reflectivity mirrors of the end masses. These mirrors are multilayer stacks composed of alternating layers of Ti:Ta2O2 and SiO2, with the main source of thermal noise being the mechanical loss of the Ti:Ta2O5.
In this project we carry out detailed material investigations aimed at elucidating how microstructure, and bonding are linked to mechanical loss in the high index material in the multilayer stack. We use x-ray diffraction to assess how the morphology of the films evolves with annealing, x-ray photoelectron spectroscopy to assess bonding. We collaborate with the CALTECH LIGO group to measure mechanical loss.
The following projects are ongoing:
- Study of microstructure and bonding on Ti:Ta2O5 and associated mechanical loss
- Investigations of SiO2:Ta2O5 mixtures and nano-laminates to understand fundamental mechanisms of crystallization and associated mechanical los
- Exploration of different dopants into Ta2O5 with the goal to find alternatives to Ti to reduce mechanical loss; i.e. using Hf, Sc, Y.
- Exploration of alloys other than Ta2O5 for high index layers and low mechanical loss coatings. We are depositing by ion beam sputtering a suite of alloys that include GeO2, HfO2, ZrO2, Sc2O3, and others in pursue of materials with a lower mechanical loss.
- Study of the organization at medium range of amorphous oxides, which is paramount to minimizing elastic energy loss in the coatings.
- Engineering of multilayer dielectric coatings for the mirrors of the end-test masses of gravitational wave interferometers.
Funding
Project funded by NSF through the LIGO program and the NSF/Moore Foundation Center for Coatings Research