Outer Zone Redness on AR coatings

**Falstaff** · 05-25-2012, 05:27 AM

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

**Mauro.Airoldi** · 05-29-2012, 08:07 AM

If you reduce the thickness of AR the reflection in the center of the lens can be more blue but on the edge you'll see red.
More, caused the different base of the lenses, hight is the base more shift to left is the reflection curve (and red came from the right part of the lens).
See the picture, in blue the right curve, in green the curve shift of 5 %

**Mauro.Airoldi** · 05-29-2012, 08:11 AM

sorry the picture...

Click image for larger version.

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**dsenk33** · 06-06-2012, 03:24 PM

what kind of rings are you using ? what type of chamber ? The red is a common thing with a green hue, purple is also common with a blue hue. In my experience, in most cases, after edging and the lens cooling a bit this usually goes away.

**dsenk33** · 06-06-2012, 03:26 PM

also, half moon effect is when a lens slips down a dome causing a what looks like a hal-moon on the lens.

**Falstaff** · 06-08-2012, 08:48 AM

Thank you for the replies.

We use Leybold AR coating machines. The calotte rings are just ordinary metal sizing rings, the same as we have always used. There are no mechanisms to flip the lenses over at the end of each run for example. There is not really any possibility of a lens slipping out of the rings completely, but it is possible that a tightly fitting lens could be wedged in at a small angle.

I believe that the usage of the term 'half-moon' effect by the Germans was a generalisation of something that looks like the phases of the moon. I have never seen a 'half moon', but there are crescents, usually slender. If this is just due to the angle presented by the curved lens to the coating plume, then I would expect to see a ring around the outside. I do not understand why there are sometimes just crescents of red colour.

Many thanks.

Falstaff

**Chris Ryser** · 06-10-2012, 07:27 AM

Have you checked with and without hydrophobic coatings, is there any difference ?

**Falstaff** · 06-12-2012, 02:12 AM

Actually, I have not checked the hydrophobic coating out with respect to this matter. We do have some problems with hydrophobic coatings on the bottom calotte rows. The hydrophobic properties are often weaker there, but it had never occurred to me that this could be making an optical difference.
It would certainly be worth checking this out. Thank you.

Falstaff

**sharpstick777** · 06-20-2012, 04:19 PM

Why did you move away from green toward blue? most people use green simply because the color stays more constant between batches and across the lens. Your issue could be with the process.

Did you switch the entire process to a "blue" process or are you mixing elements from the "green" process you previously used? Your machine may need a firmware update as well, or different settings for your "blue" AR. Contact your process manufacturer, or Leybold, chances are they have seen the issue and have a fix already.

**Falstaff** · 07-06-2012, 05:42 AM

It is not actually a blue process, only shifted towards the blue. It is still basically a green coating. The decision to make the change happened higher up in the company, and it is not something I can take it upon myself to change back again.
Thanks to your comments, I am coming to the view that the process we have now is perhaps a little unforgiving, causing the colour to not always be constant across a lens if there are small irregularities in the calottes, rings etc. Highly curved lenses will have a thinner coating in the outer zones, and this appears red now instead of still green.

Many thanks,

Falstaff

**Mike K** · 07-08-2012, 03:20 PM

Hello everyone,

I'm new to this forum and really glad that we can share our experiences here. I work as an AR machine operator at ophthalmic laboratory in Poland. We tend to treat the outer redness as something naturally occuring in the process. That usually happens with high curvature lenses (the angled surface tends to receive less material). We have tried numerous methods in order to reduce that effect and nothing seems sufficient. Different position in the holder, temperature change and removing the hydrophobic layer had no positive effect.

The worst case scenario are high base and big diameter lenses. For example, coating the 80mm diameter and 8+ base lens results in over 20mm thick reddish ring. We are really looking into the problem and haven't found any solution yet.

We were wondering if changing the recipe would do any good. Increasing the layers thickness would result in higher residue on outer layers but still change the center colour significantly.

Any kind of advice would be most welcome.

Best Regards,
Mike

**IC-UC** · 07-10-2012, 08:01 PM

What you may be seeing is that one or more of your layers is burning off too rapidly. You can check this by running test samples from top to bottom in the callotte and measuring to see if the thickness is uniform.

**sujeet** · 05-08-2013, 03:56 PM

Hi Chris,

I have an issue with one of my small coater. Chamber size is around 700ltrs. Typical configuration. 4 pocket eb Gun, Diff polycold, roots rotary combo.
Here is the problem.
Say, we did a process with Superhydrophobic as last layer.
Next run, after the Ion etching ( Mark I ) it takes forever to get back the vacuum ( sometime 30-40 min ). During etching the vacuum is around 2 e-4 and my process starting vacuum is aroun 2.2e-5.
Checked everything. No issues if no hydrophobic is done. Any clues other than the fact the Hydrophobic from previous run sticks on the wall and Ion source etches it out and degasses. Any solutions, sir ?

**Falstaff** · 05-10-2013, 01:17 AM

Hi sujeet,

We have not encountered this particular problem, although we have only just begun to investigate the use of a superhydrophobic pill. It does sound like your superhydrophobic treatment is causing you problems. Do have the option of reducing the thickness of this layer without compromising the properties? It may just be worth checking the power settings for this layer too. We do not attempt the full manufacturer's advised thickness. One other thing which has caused us problems is the type of shot blast used to clean the shields. The amount of physical etching to the surfaces obviously has an effect on the what adheres during the processes.
Sorry, that is all I can think of at the moment.

Best Regards,

Falstaff

**Chris Ryser** · 05-22-2013, 03:12 AM

Originally Posted by sujeet

Checked everything. No issues if no hydrophobic is done. Any clues other than the fact the Hydrophobic from previous run sticks on the wall and Ion source etches it out and degasses. Any solutions, sir ?

The solution would be a good periodic , or as necessary a cleaning of your walls with an AR stripper. Another solution is also to apply a chemical Super Hydrophobic layer that is done outside the vacuum chamber, cures with contact to oxygene and will not pollute the coating machine.

check it out at --------------------> http://optochemicals.com/crystalclear.htm