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arXiv · 2603.14322

Thermal Noise Reduction in Ternary Optical Coatings: From Ti::GeO$_2$-Based Ternary Systems to High Index Materials

Vincenzo Pierro·Guerino Avallone·Jessica Steinlechner·Marco Bazzan·Francesco Chiadini·Roberta De Simone·Marianna Fazio·Massimo Granata·Veronica Granata·Gerardo Iannone·Graeme McGhee·Carmen S Menoni·Christophe Michel·Vincenzo Fiumara
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Abstract

Minimizing coating thermal noise is crucial for enhancing gravitational wave detector sensitivity, with a target Amplitude Spectral Density Reduction Factor (ASD RF) of $0.5$ relative to standard coatings. This study investigates the design of low-noise dielectric stacks using the 'Double Stack of Doublet' strategy, explored via ad-hoc optimization heuristics specifically developed for efficient parametric analysis of coating performance. We analyze the performance limits of ternary coatings based on SiO$_2$, Ti::SiO$_2$, and Ti::GeO$_2$, considering material property uncertainties and absorption constraints. Optimization results show that this system, even with relaxed absorbance constraint (1 ppm), falls short of the target, achieving a best ASD RF of $\sim 0.69$. Consequently, we explore alternative ternary 'Double Stack of Doublet' designs incorporating higher-refractive-index materials. Simulations demonstrate that incorporating alternative high-index materials offers a promising pathway, potentially enabling the achievement of the project target. We discuss the optimization strategies, performance trade-offs, design robustness, and implications of using high-index, potentially higher-loss materials for next-generation optical coatings.

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Vincenzo Pierro, Guerino Avallone, Jessica Steinlechner, Marco Bazzan, Francesco Chiadini, Roberta De Simone, Marianna Fazio, Massimo Granata, Veronica Granata, Gerardo Iannone, Graeme McGhee, Carmen S Menoni, Christophe Michel, Vincenzo Fiumara. 2026-03-15. Thermal Noise Reduction in Ternary Optical Coatings: From Ti::GeO$_2$-Based Ternary Systems to High Index Materials. https://doi.org/10.1103/76xz-q8k1

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