LIGO Seminar

Ultrastable optical interferometers require mirrors that simultaneously

exhibit excellent optical and mechanical quality. The current bounds of

stability and sensitivity in these systems are dictated by the mechanical

dissipation, and thus the corresponding Brownian noise level, of the

high-reflectivity coatings that comprise the cavity end mirrors. A spin-off

of fundamental quantum optics research from the University of Vienna,

Crystalline Mirror Solutions has developed a novel microfabrication

technique that enables the transfer of low-loss single-crystal semiconductor

heterostructures onto essentially arbitrary optical surfaces. These

"crystalline coatings" simultaneously exhibit both high reflectivity and

minimal mechanical damping, with room temperature loss angles experimentally

demonstrated to be an order of magnitude below that of ion-beam sputtered

(IBS) dielectric coatings. In the past, however, the ultimately achievable

optical performance, as well as the maximum attainable coating diameter have

been called into question. Since our original demonstration of this

technology in 2013, we have undertaken a focused optimization effort to

address both of these challenges. This has culminated in the reproducible

realization of optical properties that are on par with those of IBS coatings

including parts-per-million levels of optical scatter and sub-ppm absorption

for center wavelengths spanning 1000 to 1600 nm. In parallel, we have now

demonstrated coating sizes from the single cm level up to diameters of 10

cm, with a clear path to manufacture 20-cm transferred coatings. In this

presentation I outline the development steps envisaged for the successful

scaling of these optics to "LIGO relevant" diameters of 30+ cm and describe

the potential for the successful implementation of crystalline coatings in

gravitational wave astronomy.