remove AR coating on anamorphic prism?

Ok, here is a strange request.

I realized (with great joy) that I have 3 sets of amamorphic prisms. I removed them years ago from a very high tech worm drive (they were about $5000 new each!) They were broken of coarse.

My problem is that they have an AR coating for 650-660nm. I know this because these drives wrote to DVD RAM type discs.

I would LOVE to use them for my 445s. However the 445 simply refect off the prisms and a tiny amount goes through. So I need to "rub off" the AR coating.

Can this be done without damage to the prisms?

Not typically, you'll probably just make a mess if you would attept to rub/sand/etc the coatings off. It might be possible to dissolve them off using, for example, acetone. This could also end up in a big mess and complete loss of the prisms though.

There are several different methods outlined throughout the net.. I have even tried
using sunscreen spf 30 for its content of fine particulate matter... No dice.

Doing it with straight up chemicals, metal polishes etc will either etch or outright
scratch the glass..

The better the optics, the better the coatings. Some places offer a service, or so ive
heard.. Havent found one yet.. Got 30 pairs myself which are coated for 808.
I simply ate the losses, and am still looking.

I did read an post on an optics forum where a gent had worn off the coating
with his eye lashes... He also mentioned that it took 30+ years on his microscope :thinking:



EDIT*

Google a product called 'AR Stripper'. This seems to be the most repeated item that ive heard
of, but never tried.

Also found this..

"The oldest formula to remove AR coatings used to be a mix of sulphuric and boric acid and it had to be heated. When too much heat was applied it exploded. Not too many coating labs are still doing this one. But protection should always be there."

Thanks for the info.

Damn, I thought there would be a quick and easy solution. ie: dip it in alcohol
Sounds like they use hydrofluoric acids....that a dangerous acid to play with.
I may try leave the prism in sulphuric acid for a few days and see what happens. Sulphuric doesn't react with glass so hopefully they'll be no damage to the prism

The uncoated prisms will still be very lossy, it may be better to use them for the wavelength range of their coating and find another solution for your 445nm.

Bluefan said:

The uncoated prisms will still be very lossy, it may be better to use them for the wavelength range of their coating and find another solution for your 445nm.

Click to expand...

The ones I have coated for 808 drop the output around 30%. Id imagine ones
coated for 650-660 will drop even less, so it wont be too bad considering
the clean shape and improved divergence.

How would an uncoated pair bring about higher loss? Always thought
that no coating is better than the wrong coating..

Personally, I dont have much experience with AR coatings, but
the prisms ive tried make for a very welcome improvement with
the 445 LD's even with the losses..

I don't expect them to perform much better, I'd say a 30% is much, but it depends on what you finds more important, the beam shape or power.
Without coating they probably won't perform much better, but it really depends on how the AR coating behaves at 445nm.

The only way to strip a modern hard AR coating is to have a optician polish it off on a Zeiss or Draper machine and then have it recoated. Silicon dioxide and TiO2 do not dissolve easily.

Live with the existing coatings. Trust me on this.

Steve

It depends on the coating entirely though. If its a hard, mineral, coating, chances of chemical removal are slim. If its a plastic based coating you can remove it chemically try anything that doesnt damage glass.

If you can't get it off using solvents like acetone, you can try a more harsh approach using sulfuric acid or even aqua regia, which don't damage BK7 glass, but will destroy virtuall all organic materials.

Hydrofluoric acid wouldn't not be reccommended due to its extreme danger and ability to attack the glass - you could lose both a hand and your prism messing with that.