How thick is an AR coat...and more

[Uncle Fester]

Let's beat this AR dead horse some more because hey- why not!

I recently took an online CE from Jobson "Everything Old is New Again- Lens Treatments".

I can't locate the paper copy I made of article but I do have the answer sheet and it brought up a question that I remember was on my mind from the thread below, as well as a couple others.

From the test was an answer that AR improved 91% transmittance about 8% (leaving 1% blocked) with AR on cr39 than without.

Another was the thickness of an AR coat. Concerning thickness I remembered 10 or more years ago reading that the coat was angstroms thick and brought that up in the linked thread below only to be shot down by Mike Aurelius and MakeOptics. Two Titans I respect (even if Make does diss me;) saying it's .2 to .3 microns not angstroms (2,000 to 3,000). I distinctly remember the article used for the test saying it was angstroms thick so am I correct that the author, like me, got it wrong?

Here's the thread and I think the mag fluoride discussion is today's special sauce for the Crizal Rock. No?


https://www.optiboard.com/forums/sho...ick+coating%3F

please excuse my ignorance hanging out for the world to see....again!

[Uncle Fester]

Found the article so I quote:

"An AR coat is less than a 1/4 wave length of light thick and is measured in angstroms because it is so thin. An angstrom unit is one tenth of a billionth of a meter. Ideally the index of the AR coating should have the same refractive index as the lens to which it is applied, but this is not always the case."

[Mauro.Airoldi]

ARs have been my daily bread for 30 years (of which 10 as a process engineer for the world's leading manufacturer of AR implants), let's see if I can clarify a few things:
1 measuring the thickness in amstrongs or nanometers is the same thing except that the amstrongs are 1/10 of a nanometer. the amstrong is no longer in use as a unit only because you prefer to define the quantities as a function of 1000 (meter, millimeter, micron, nanometer)
2 Yes, the thickness of an AR can vary from 200 to 600 nm, in the case of particular filters used at an industrial level (as in the case of optical fibers) the thickness can reach the order of microns (even 50/100 different layers) for our lenses the layers usually range from a minimum of 4 to 10-15
3 The transmission of an MR7 -Poly lens is about 90%, with a good AR you can get up to 98 / 98.5% average
4 I don't think magnesium fluoride is integrated into the Rock because it requires a very high lens temperature to adhere (250-300 ° c) which is not compatible with plastic lenses but only with mineral lenses
if you have other questions it is a pleasure to answer you

[KrystleClear]

Wow. Out of curiosity and for better understanding I googled how many microns the thickness of paper is - and it's an average of 100 microns. Obviously I knew a coating would be much thinner than paper but dang!

I feel more prepared for the next fitting/interrogation I have with an engineer.

[Uncle Fester]

Thanks Mauro! A great explanation. I deal with many engineers and can usually hold my own but will admit that some of the even simple mathematics for an engineer does not come easily to me and is why I'm an optician and not an optometrist.

Story time-
In High School I needed only two 5 credit courses to qualify to graduate and on the first day of Chemistry my teacher taught us the formula for density, I asked after class if the math got more difficult. Of course Mr Marks said "yes- much".

I then went to the guidance office and got 3rd and 4th period off since I only needed to pass band and jazz band to get the 10 credits and a diploma.

20/20 hindsight says I should have applied myself more but c'est la vie.

As Judge Smails from Caddyshack say- "Well Danny- the world needs ditch diggers too."