{"title":"Thermal noise reduction in ion-beam sputtered HfO2:Ta2O5 thin films via high-temperature treatment","authors":"Valeria Milotti , Giulio Favaro , Massimo Granata , Danièle Forest , Christophe Michel , Julien Teillon , Nicole Busdon , Marco Bazzan , Hanna Skliarova , Giacomo Ciani , Carlo Scian , Livia Conti , Shima Samandari , Valentina Venturino , Michele Magnozzi , Maurizio Canepa , Nicholas Demos , Slawomir Gras , Matthew Evans , Valérie Martinez , Anaël Lemaître","doi":"10.1016/j.optmat.2025.116901","DOIUrl":null,"url":null,"abstract":"<div><div>Reducing coating thermal noise (CTN) in mirrors for gravitational wave (GW) interferometers is pivotal to improving sensitivity in the mid-frequency range. Current mirror coatings are heat-treated (annealed) after deposition in order to partially relax their microstructure and to improve their optical and mechanical properties. The maximum annealing temperature is an important parameter in this respect as a higher thermal energy allows the system to relax to more stable configurations, which is often beneficial for the thermal noise performances of the coatings. However, the useful temperature range is limited by the stability of the amorphous microstructure, since excessive heating eventually leads to the formation of crystalline grains which are detrimental from both the mechanical and optical viewpoints. In this work, inspired by the possibility to improve glass stability in alloys by a careful choice of mixing ratios, we studied ion-beam co-sputtered amorphous HfO<sub>2</sub>:Ta<sub>2</sub>O<sub>5</sub> thin films with different HfO<sub>2</sub> concentrations, so as to identify conditions that would lead to a higher glass stability in order to explore the effects of a thermal annealing over an extended temperature range. We then deposited a multilayer mirror, alternating layers of HfO<sub>2</sub>:Ta<sub>2</sub>O<sub>5</sub> with composition providing the highest crystallization temperature and SiO<sub>2</sub> layers. The thermal Brownian noise of the mirror coating was found to decrease with increasing heat-treatment temperatures, reaching losses comparable to the Ti-doped Ta<sub>2</sub>O<sub>5</sub> coatings of Advanced LIGO when heated at the highest possible temperature. Our results demonstrate the critical importance of optimizing the film composition and annealing procedure in order to improve the coating performances and the sensitivity for the next generation of GW detectors.</div></div>","PeriodicalId":19564,"journal":{"name":"Optical Materials","volume":"163 ","pages":"Article 116901"},"PeriodicalIF":3.8000,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Optical Materials","FirstCategoryId":"88","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0925346725002617","RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATERIALS SCIENCE, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
Reducing coating thermal noise (CTN) in mirrors for gravitational wave (GW) interferometers is pivotal to improving sensitivity in the mid-frequency range. Current mirror coatings are heat-treated (annealed) after deposition in order to partially relax their microstructure and to improve their optical and mechanical properties. The maximum annealing temperature is an important parameter in this respect as a higher thermal energy allows the system to relax to more stable configurations, which is often beneficial for the thermal noise performances of the coatings. However, the useful temperature range is limited by the stability of the amorphous microstructure, since excessive heating eventually leads to the formation of crystalline grains which are detrimental from both the mechanical and optical viewpoints. In this work, inspired by the possibility to improve glass stability in alloys by a careful choice of mixing ratios, we studied ion-beam co-sputtered amorphous HfO2:Ta2O5 thin films with different HfO2 concentrations, so as to identify conditions that would lead to a higher glass stability in order to explore the effects of a thermal annealing over an extended temperature range. We then deposited a multilayer mirror, alternating layers of HfO2:Ta2O5 with composition providing the highest crystallization temperature and SiO2 layers. The thermal Brownian noise of the mirror coating was found to decrease with increasing heat-treatment temperatures, reaching losses comparable to the Ti-doped Ta2O5 coatings of Advanced LIGO when heated at the highest possible temperature. Our results demonstrate the critical importance of optimizing the film composition and annealing procedure in order to improve the coating performances and the sensitivity for the next generation of GW detectors.
期刊介绍:
Optical Materials has an open access mirror journal Optical Materials: X, sharing the same aims and scope, editorial team, submission system and rigorous peer review.
The purpose of Optical Materials is to provide a means of communication and technology transfer between researchers who are interested in materials for potential device applications. The journal publishes original papers and review articles on the design, synthesis, characterisation and applications of optical materials.
OPTICAL MATERIALS focuses on:
• Optical Properties of Material Systems;
• The Materials Aspects of Optical Phenomena;
• The Materials Aspects of Devices and Applications.
Authors can submit separate research elements describing their data to Data in Brief and methods to Methods X.