DFG-NSF: Novel Low Loss Coatings – Enabling the Third Generation of Gravitational-Wave Detectors

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100 years ago, Einstein predicted the existence of gravitational waves which are ripples in the curvature of space-time. On 14th September 2015, the (second-generation) detectors of the LIGO project made the first gravitational-wave detection.This was a ground-breaking event for fundamental physics, observing for the first time a binary black hole system merging to form a single black hole, and has opened a new window into the universe allowing us to ‘listen’ to its gravitational signatures, revealing previously hidden objects.A successful outcome of this project would enable sensitivities envisioned for the next generation gravitational-wave detectors and new discoveries in gravitational astronomy, e.g. the detection of new sources, an improvement of the detection rates for population studies of sources, and enable to see fainter and more distant sources.Gravitational waves cause changes of < 1e-19m in the separation of mirrors forming an interferometric detector. This is a displacement so small that the thermal vibration of the mirrors and their coatings, so called Brownian thermal noise, will limit the sensitivity of current and future detectors at the detectors’ most sensitive frequencies, where the detection of many interesting sources is expected such as merging neutron stars and spinning pulsars.In this project we will develop new materials with low thermal noise, which involves understanding the atomic processes in the materials, to enable sensitivity improvements of interferometric gravitational wave detectors.Thermal noise in highly-reflective mirror coatings is directly proportional to the coating thickness, the mechanical loss of the materials and the mirror temperature. To significantly reduce coating thermal noise, future gravitational wave detectors will be cryogenically operated. Cryogenic detectors require low optical absorption in the mirrors to minimize heating from the laser beam, and therefore maintain the cryogenic operation temperature. The aim of this project is the development of highly-reflective multilayer coatings based on studies of coating properties, composition and structure, to meet the challenging requirements on absorption, reflectivity and mechanical loss.While the proposal is mainly targeted at future cryogenic detectors, thermal noise reduction for upgrades of detectors operating at room temperature (such as Advanced LIGO and VIRGO) will also be part of the proposed research.