PDA

View Full Version : OT: Optical Glass w Polished Edges



Paul Alciatore
12-06-2004, 09:20 PM
I'm not sure how on or off topic this is but I need about eight pieces of glass that measure 3" x 5" x 1/4" thick. Or 3/8" or 1/2" thick. Sounds easy, but here's the kicker, at least two of the 1/4" edges, preferably all four, need to be optically polished to a fair degree of flatness and parallelism. They are for a college lab. They want to send a laser beam through one edge and out the opposite one and demonstrate the refraction at various angles.

I have asked a local glass supplier and he can get them at about $20 each. Sounds a bit steep to me. Anybody got any ideas where I could get something of this description for less? Or how I could polish the edges of the pieces after he supplies them rough cut?

I have already searched the optical sources I know of: Edmund, Anchor, and others with no luck. Any help would be appreciated.

Paul A.

nheng
12-06-2004, 09:46 PM
Paul, $20 sounds like a steal but I'm not sure you're gonna get optical specs for that amount.

Passing a laser beam thru a glass or small tank of water with a little milk added (and then increased) is a good demo of dispersion (of milk particles) and of optical attenuation of the beam as the beam energy is lost to dispersion.

As I typed that I realized ... you could use a small fishtank for some experiments but would need to consider the refractive index of the water to glass and glass to air interfaces. Cutting plexiglass square and polishing the edges may be another option although flatness would be difficult.

www.controloptics.com (http://www.controloptics.com) has optical components and I think my past searches indicated somewhat better pricing at the time.

If you can live with well defined end geometry and optical surface quality but at an angle, they have 74mm long dove prisms of BK7 optical glass for only $54. I say "only" because most optics are not cheap. There used to be a few domestic sources of Asian origin but the have been gobbled up by some big names like JDS Uniphase.
Den

aboard_epsilon
12-06-2004, 09:48 PM
To get the edges polished......but doupt that they will be optically flat by the following method....but worth a try if you have the time
first make a jig so that the glass edge is flush with the top of two peices of plywood.

Start with wet and dry paper of the roughest grade needed to get any ripples out.
rap it around a parrallel-like peice of steel or something....and start sanding.

start off with say 60 grit using plenty of soap and water on it .
from 60 move up to 100 grit.
then 200
then 400
then 600
then 800
then 1000
and finish off with 1200 then metal polish.
after hours of this, and spending $5 on wet and dry, you will be wishing that you had spent the $20.
This is how I've polish alloy and stainless..same rules apply to glass....I now have polishing machine, so now I omit from the 100 grit stage on.
all the best...mark

Evan
12-06-2004, 09:55 PM
$20 sounds cheap to me. If you try and do it yourself it will be very time consuming.

nheng
12-06-2004, 10:13 PM
Having the edges meet some specs unfortunately turns the two hunks of glass into prism grade products.

Most optical components have edges which are scribed or cut and ground to finished size. When ground, they usually have a fairly coarse, diffuse surface finish.

added - I'd give polycarbonate sheet a shot. You'll have considerable control over geometry and finish. Working an edge up to fine finish is not that difficult. Start with a clean cut and wet sand up to around 600 or 800 grit then move to a buffing compound. Buffing the edge will round over the edges slightly but your laser should be entering near the center of the thickness.

[This message has been edited by nheng (edited 12-06-2004).]

darryl
12-06-2004, 11:06 PM
Another idea- how about using some clear casting resin. Make a mold where one side is a vertical piece of glass, the opposing side is also glass, but several short sections, each at a slightly different angles. Make note of each angle for the sake of the experiment. Some carefully applied silicon rubber will glue the edges together so no leakage occurs when you pour the resin into it. The ends of the mold can be anything as no light will be shone through there.