The first detection of gravitational waves, and in particular the observation of merging black holes, which otherwise appear 'dark', has been one of the most exciting scientific achievements of the last decades.
With the next generation of even more sensitive detectors, we plan to be able to see gravitational waves from objects as far away as the edge of the observable Universe. However, a major limitation to the sensitivity of these detectors is the thermal noise of their core components: the highly-reflective coated interferometer mirrors.
The use of cryogenic temperatures will be a major step forward in thermal-noise reduction. However, with current coating technology, the sensitivity goals of next generation detectors cannot be met, not to mention further upgrades or future detector generations:
(a) All amorphous coating materials, identified so far, with low thermal noise at low temperatures, show too high optical absorption.
(b) Mono-crystalline coatings can show both low thermal noise and low absorption, but come with different obstacles such as limitations on the size and material combinations, or different noise mechanisms e.g. from bonding the coating to the mirror.
I plan to explore a completely new path to realize coating-free mirrors: The use of ion implantation to create a highly-reflective multilayer structure directly inside the silicon mirror substrate.
In this project, my team and I will explore if the implantation procedure preserves the excellent optical and thermal-noise properties of crystalline materials, which cannot be met by amorphous coatings, while not imposing the size and material limitations of single-crystalline coatings. To be fully in control of the parameters, we will use our own implanter to create layers in crystalline silicon substrates, characterize the layers’ properties and investigate the optimum implantation and post-implantation treatment conditions in order to create the best possible mirror performance.
A successful realization of such mirrors will solve the coating thermal noise issue in gravitational-wave detectors, allowing for an unhindered view into the Universe.
