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This content will become publicly available on January 9, 2024

Title: Imaging scatterometer for observing in situ changes to optical coatings during air annealing

Annealing of amorphous optical coatings has been shown to generally reduce optical absorption, optical scattering, and mechanical loss, with higher temperature annealing giving better results. The achievable maximum temperatures are limited to the levels at which coating damage, such as crystallization, cracking, or bubbling, will occur. Coating damage caused by heating is typically only observed statically after annealing. An experimental method to dynamically observe how and over what temperature range such damage occurs during annealing is desirable as its results could inform manufacturing and annealing processes to ultimately achieve better coating performance. We developed a new, to the best of our knowledge, instrument that features an industrial annealing oven with holes cut into its sides for viewports to illuminate optical samples and observe their coating scatter and eventual damage mechanismsin situand in real time during annealing. We present results that demonstratein situobservation of changes to titania-doped tantala coatings on fused silica substrates. We obtain a spatial image (mapping) of the evolution of these changes during annealing, an advantage overxray diffraction, electron beam, or Raman methods. We infer, based on other experiments in the literature, these changes to be due to crystallization. We further discuss the more » utility of this apparatus for observing other forms of coating damage such as cracking and blisters.

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Publication Date:
Journal Name:
Applied Optics
Page Range or eLocation-ID:
Article No. B97
1559-128X; APOPAI
Optical Society of America
Sponsoring Org:
National Science Foundation
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