Experimental Realization of Optimized Ternary Mirror Coatings

TL;DR

This paper demonstrates the first experimental realization of multi-material dielectric mirror coatings optimized to reduce thermal noise and optical losses, validating the design approach through fabrication and characterization of two ternary systems.

Contribution

It introduces a novel multi-objective optimization method for designing complex dielectric coatings and successfully fabricates two ternary systems, validating the approach experimentally.

Findings

SiNx coating reduces noise by 0.82 compared to references

Ti:GeO2 coating achieves sub-ppm optical absorption

Discrepancy in thermal noise suggests manufacturing process improvements

Abstract

We report on the first experimental realization of multi-material dielectric mirror coatings designed through a multi-objective optimization algorithm to simultaneously minimize thermal noise and optical losses. We validate this design strategy by fabricating and characterizing two distinct ternary systems: a SiNx -based proof-of-concept and a Ti:GeO2 -based system targeting lower optical losses. The performance of the SiN x coating shows remarkable agreement with predictions, demonstrating a noise amplitude spectral density reduction of 0.82 with respect to current reference coatings, and validating our design-to-fabrication pipeline. The Ti:GeO2 -based system achieves the crucial goal of sub-ppm absorption; its measured thermal noise, however, is higher than the theoretically predicted level of 0.71, extrapolated from single-layer material characterization. A dedicated tolerance analysis confirms that this discrepancy is not attributable to random thickness errors, emphasizing that further studies of the manufacturing process are needed to fully exploit this combination of materials. This work establishes a robust methodology for producing complex, high-performance optical coatings tailored for precision experiments.