We produce AR coatings with a green reflex colour. Recently, we have changed our colour somewhat and the spectral curve hass moved towards the blue part of the spectrum.
Sometimes, especially with lenses in the lowest calotte positions, we see a redness around the edge. Typically, this does not go all the way around the outside to make a ring. We are familiar with the redness due to the line of sight in the outer zones of curved lenses.
This is not just due to the angle of viewing, because movement and rotation of the affected lenses under an inspection lamp makes no difference.
Scanning with a spectrophotometer reveals that the coating is physically thinner where it is red. Presumably, this is because of the curvature of the lenses as coating material is applied in the vacuum chamber.
Has anyone seen this before, and is there a fix?
A visiting Process Engineer, once described an effect which he called 'half moon' effect. I wonder if this is he same as we have here.
Many thanks,
Falstaff
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