Sapphire Optics

[drawoh]

I am working on an optical system that must be sealed to IP65 and will be used in a mine. There is very little room in the housing because we are going for the largest aperture possible and the smallest housing. If I glue the window in with RTV, I will save space and it will be sealed and somewhat shock protected. I expect this thing to be abused.

Has anyone here worked with sapphire windows? I understand they are scratch resistant. How shatter resistant are they?

My alternate design is a glass window with a clamp. This will be cheap enough that we can ship spares, and fairly easy to replace, but I would rather not provide the space for it, especially if I want my seal to work.

Thanks.

JHG

 

[IRstuff]

How thick is the window going to be? If you expect it to survive impacts, then you'd need tempered glass.

Sapphire is used for windows for a variety of applications (

http://www.crystalsystems.com/abssa.html),

but it's probably much more expensive than tempered glass.

TTFN

 

[drawoh]

IRstuff,

I do not know yet how thick it will be. The vendor's manuals claim that it can be thinner than a glass window, but I do not know what the parameters are.

It will be more expensive than the first glass window. After that, it depends on what we break.

JHG

 

[IRstuff]

If you expect lots of impacts, then you'll need some sort of grid or other sacrificial agent.

TTFN

 

[MikeHalloran]

Sapphire in simple geometries and modest sizes is surprisingly, well, not all that expensive. And it is hard and strong.

It's also birefringent. Beware.



Mike Halloran
Pembroke Pines, FL, USA

 

[canyoncruz]

For shock resistance you want to go as thin as you can. The integrity of the mount is most imprtanat. Depending on how you mount, any flexure will crack the window.

There are several way to mount the window. If space is critical, i would sugest a cirular window. Machine the mount so that the window rests on a "knife edge".

To adhear, you best choicese are:
Glass frit (Dimet)
Structural epoxy, optically match, (TRA-CON 2151 I think)
RTV, theopticl standard being RTV 566

If you are making many of these, I suggest the Glass frit activiated with and inductor, for experiment, you can just stick you assembly in the oven.

Material choice is probably the most important.

CTE MUST BE MATCHED!!

Quartz, Saphire - Invar or zerodur
Pyrezt, BK7 - Kovar
Amorphus Quartz - Titanium
And so on


Hopw this helps

 

[drawoh]

canyoncruz,

My plan with the RTV was to fixture the window about 1mm away from the structure, then fill the void with RTV. This provides some springyness and it works around thermal expansion somewhat. I am trying to save weight. I strongly prefer aluminium to invar.

Definitely, I will look into your RTV specification. Thank you very much.

JHG

 

[jedward]

Fastening saphire windows with GE rtv 566 with a 1 mm bond gap will probably be the best you can do BUT you must use the recommended primer and allow it to fully cure. (equivalent material is nusil cv2566)

_A fem analysis would set some guidelines for performance but will not likely deal with scratches, titanium mount hardware is probably best thermal match next to Kovar or Invar.
-Book by P Yoder on mounting optical element recommended reading.
-Alternate may be 3M 2216 translucent bonding which remains somewhat flexible and is good at high temperatures as is the 566. Also consider DC 1104