Thermal noise reduction in ion-beam sputtered HfO2:Ta2O5 thin films via high-temperature treatment

IF 3.8 3区 材料科学 Q2 MATERIALS SCIENCE, MULTIDISCIPLINARY
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
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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.

Abstract Image

离子束溅射HfO2:Ta2O5薄膜高温处理降低热噪声
降低引力波干涉仪反射镜的涂层热噪声(CTN)是提高中频灵敏度的关键。目前的反射镜涂层在沉积后进行热处理(退火),以部分放松其微观结构并改善其光学和机械性能。在这方面,最大退火温度是一个重要的参数,因为较高的热能可以使系统松弛到更稳定的结构,这通常有利于涂层的热噪声性能。然而,有效的温度范围受到非晶结构稳定性的限制,因为过度加热最终会导致晶体颗粒的形成,这从机械和光学角度来看都是有害的。在这项工作中,受到通过精心选择混合比例来提高合金玻璃稳定性的可能性的启发,我们研究了具有不同HfO2浓度的离子束共溅射非晶HfO2:Ta2O5薄膜,以确定导致更高玻璃稳定性的条件,从而探索在更大温度范围内热退火的影响。然后,我们沉积了一个多层镜面,交替层的HfO2:Ta2O5的组成提供了最高的结晶温度和SiO2层。随着热处理温度的升高,镜面涂层的热布朗噪声降低,达到与先进LIGO的掺钛Ta2O5涂层在最高温度下加热时的损失相当。我们的研究结果表明,优化薄膜组成和退火工艺对于提高下一代GW探测器的涂层性能和灵敏度至关重要。
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来源期刊
Optical Materials
Optical Materials 工程技术-材料科学:综合
CiteScore
6.60
自引率
12.80%
发文量
1265
审稿时长
38 days
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.
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