Abernathy Matthew R, Hough James, Martin Iain W, Rowan Sheila, Oyen Michelle, Linn Courtney, Faller James E
Appl Opt. 2014 May 20;53(15):3196-202. doi: 10.1364/AO.53.003196.
The current generation of advanced gravitational wave detectors utilize titania-doped tantala/silica multilayer stacks for their mirror coatings. The properties of the low-refractive-index silica are well known; however, in the absence of detailed direct measurements, the material parameters of Young's modulus and coefficient of thermal expansion (CTE) of the high refractive index material, titania-doped tantala, have been assumed to be equal to values measured for pure tantala coatings. In order to ascertain the true values necessary for thermal noise calculations, we have undertaken measurements of Young's modulus and CTE through the use of nanoindentation and thermal-bending measurements. The measurements were designed to assess the effects of titania-doping concentration and post-deposition heat-treatment on the measured values in order to evaluate the possibility of optimizing material parameters to further improve thermal noise in the detector. Young's modulus measurements on pure tantala and 25% and 55% titania-doped tantala show a wide range of values, from 132 to 177 GPa, which are dependent on both titania concentration and heat-treatment. Measurements of CTE give values of (3.9±0.1)×10⁻⁶ K⁻¹ and (4.9±0.3)×10⁻⁶ K⁻¹ for 25% and 55% titania-doped tantala, respectively, without dependence on post-deposition heat-treatment.
当前一代先进的引力波探测器在其镜面涂层中采用了掺杂二氧化钛的钽酸镧/二氧化硅多层堆叠结构。低折射率二氧化硅的特性是众所周知的；然而，在缺乏详细直接测量的情况下，高折射率材料——掺杂二氧化钛的钽酸镧的杨氏模量和热膨胀系数（CTE）的材料参数一直被假定等于纯钽酸镧涂层的测量值。为了确定热噪声计算所需的真实值，我们通过纳米压痕和热弯曲测量对杨氏模量和CTE进行了测量。这些测量旨在评估二氧化钛掺杂浓度和沉积后热处理对测量值的影响，以便评估优化材料参数以进一步降低探测器热噪声的可能性。对纯钽酸镧以及掺杂25%和55%二氧化钛的钽酸镧的杨氏模量测量显示出很宽的取值范围，从132到177吉帕，这取决于二氧化钛浓度和热处理。对CTE的测量得出，掺杂25%和55%二氧化钛的钽酸镧的CTE值分别为(3.9±0.1)×10⁻⁶ K⁻¹和(4.9±0.3)×10⁻⁶ K⁻¹，且与沉积后热处理无关。
