Effect of heating treatment and mixture on optical properties of coating materials used in gravitational-wave detectors
Effect of heating treatment and mixture on optical properties of coating materials used in gravitational-wave detectors
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DOI：
10.1116/1.5122661
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发表时间：
2019-11-01
影响因子：
1.4
通讯作者：
Cagnoli, Gianpietro
中科院分区：
文献类型：
--
作者：
Amato, Alex;Terreni, Silvana;Cagnoli, Gianpietro
重力波探测器（GWD）的干涉仪镜子是由替代无定形二氧化硅（SIO2）和二氧化钛掺杂的Tantala（TiO2：TA2O5）层制成的Bragg反射器，分别为低和高繁殖的索引材料。通常进行热处理以减少涂料的机械损失和近红外（NIR）光吸收。作者提出了对退火和Ti：TA混合对TA2O5涂层的影响的光谱椭圆法（SE）研究，该涂层在与GWD的构建镜子相似的条件下沉积的条件下。宽带分析涵盖了NIR和基本吸收阈值区域。数据表明，退火引起的基本光吸收拓宽减少。通过Cody-Lorentz公式对数据进行建模证实，NIR吸收率低于SE敏感性，并显示出显着退火引起的所谓Urbach尾巴的减少。 Tantala掺杂二氧化钛可稍微降低了Urbach的能量。加热处理后，掺杂材料的urbach能量低于退火的纯tantala。观察到的urbach尾巴的减少很重要，因为它与机械测量中观察到的所谓内部摩擦的降低相似，因此SE成为敏捷的诊断敏捷工具，用于敏捷的诊断非晶氧化物涂层的光学和机械质量。
The interferometer mirrors of gravitational-wave detectors (GWDs) are Bragg reflectors made of alternate amorphous silica (SiO2) and titania-doped tantala (TiO2:Ta2O5) layers as low- and high-refractive index materials, respectively. A thermal treatment is usually performed to reduce both mechanical losses and near-infrared (NIR) optical absorptions of the coatings. The authors present a spectroscopic ellipsometry (SE) investigation of the effect of annealing and Ti:Ta mixing on Ta2O5 coatings deposited under conditions similar to those adopted for building up mirrors of GWDs. The broadband analysis covers both the NIR and the fundamental absorption threshold region. The data show an evident annealing-induced reduction of the fundamental optical absorption broadening. Modeling the data through the Cody-Lorentz formula confirms that NIR absorptions are below the SE sensitivity and shows a notable annealing-induced reduction of so-called Urbach tails. Titania-doping of tantala slightly reduces the Urbach energy. After the heating treatment, the resulting Urbach energy of the doped material is lower than that of annealed pure tantala. The observed reduction of Urbach tails is important because it parallels the reduction of the so-called internal friction observed in mechanical measurements so that SE emerges as a convenient tool for an agile diagnostic of both the optical and the mechanical quality of amorphous oxide coatings.