Investigation of the Young's modulus and thermal expansion of amorphous titania-doped tantala films

Abstract

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, dependent on both titania concentration and heat-treatment. Measurements of CTE give values of (3.9 +/- 0.1) x 10^-6 K^-1 and (4.9 +/- 0.3) x 10^-6 K^-1 for 25% and 55% titania-doped tantala, respectively, without dependence on post-deposition heat-treatment.

8 pages, 6 figures, Submitted to Applied Optics

References in corpus (3)

• Titania-doped tantala/silica coatings for gravitational-wave detection
• Thermo-optic noise in coated mirrors for high-precision optical measurements
• Measurements of a low temperature mechanical dissipation peak in a single layer of Ta2O5 doped with TiO2

Cited by in corpus (6)

• Amorphous optical coatings of present gravitational-wave interferometers
• Mechanical loss in state-of-the-art amorphous optical coatings
• Structure and morphology of low mechanical loss TiO${}_2$-doped Ta${}_2$O${}_5$
• Material loss angles from direct measurements of broadband thermal noise
• A new method of probing mechanical losses of coatings at cryogenic temperatures
• Strategies to reduce the thermoelastic loss of multimaterial coated finite substrates