  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 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 mechanisms in-situ and in
real-time during annealing. We present results that demonstrate in-situ
observation 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 over x-ray 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 utility of this
apparatus for observing other forms of coating damage such as cracking and
blisters.
