Abstract

Optical coatings formed from amorphous oxide thin films have many applications in precision measurements. The Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo use coatings of ${\rm{Si}}{{\rm{O}}_2}$ (silica) and ${\rm{Ti}}{{\rm{O}}_2}:{\rm{T}}{{\rm{a}}_2}{{\rm{O}}_5}$ (titania-doped tantala) and post-deposition annealing to 500°C to achieve low thermal noise and low optical absorption. Optical scattering by these coatings is a key limit to the sensitivity of the detectors. This paper describes optical scattering measurements for single-layer, ion-beam-sputtered thin films on fused silica substrates: two samples of ${\rm{T}}{{\rm{a}}_2}{{\rm{O}}_5}$ and two of ${\rm{Ti}}{{\rm{O}}_2}:{\rm{T}}{{\rm{a}}_2}{{\rm{O}}_5}$. Using an imaging scatterometer at a fixed scattering angle of 12.8°, in-situ changes in the optical scatter of each sample were assessed during post-deposition annealing to 500°C in vacuum. The scatter of three of the four coated optics was observed to decrease during the annealing process, by 25–30% for tantala and up to 74% for titania-doped tantala, while the scatter from the fourth sample held constant. Angle-resolved scatter measurements performed before and after vacuum annealing suggest some improvement in three of the four samples. These results demonstrate that post-deposition, high-temperature annealing of single-layer tantala and titania-doped tantala thin films in vacuum does not lead to an increase in scatter, and may actually improve their scatter.

© 2021 Optical Society of America

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Supplementary Material (2)

NameDescription
» Visualization 1       Sample PL4514 during annealing VAS.
» Visualization 2       Sample PL4514 after annealing ARS.

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