Question about glass/optics

tres · 4 Jul 2020 at 21:34

OCUK is probably the most eclectic group I know, so here's hoping someone might know about optics..

I want to enclose a laser light source (projector) in a cabinet, and would like to cover said source with a glass panel. The laser projector & cabinet sit just next to the wall it projects on to.

I've gone down a Wikipedia hole reading about different glass compositions and refractions, but need some more expert advice.

what would be an ideal glass to use for the cabinet top, whilst minimizing refractive distortion?

(Existing cabinets that incorporate a glass top cost about 10k)

Thanks!!

lunar · 5 Jul 2020 at 08:49

Not possible. The laser light would reflect of the surfaces and lose energy. Eventually, it would go dark. That would not take long as light travels at 300, 000 km per second.
I think diamond has the highest refractive index that prevent light escaping from the crystal.

LOAM · 5 Jul 2020 at 08:58

I can't work out what you're trying to achieve.

NVP · 5 Jul 2020 at 09:03

Cut a circular hole out of the glass for the lens.

(I'm not smart enough to help with your actual question I'm afraid, my optical physics course was many many moons ago and my knowledge of glass is limited to lead crystal for brandy!)

Dis86 · 5 Jul 2020 at 09:46

My immediate thought is quartz glass. It tends to typically be very transparent hence it's use in experimentation and uv sterilisation.

Kenai · 5 Jul 2020 at 10:11

LOAM said:
I can't work out what you're trying to achieve.

He wants to put a projector inside a cabinet with a glass front on it I think, so is looking for glass that won't distort the projection.

I'm assuming he's already got a plan to stop it overheating rapidly from being in a cabinet.

lord filbuster · 5 Jul 2020 at 15:35

They do make special projector glass windows for cinema projection rooms, but it's relatively expensive, and for the proper impact and fire rated stuff, I can't even find prices.

The index of refraction is going to be basically the same for any glass you'd be able to get hold of easily, so it's basically irrelevant. The main thing to keep refraction down is to keep the angle of incoming light as close to 90 as possible, the light needs to enter the glass perpendicularly, so that means the projector is going to need to be as close as possible to the window, especially if it's short throw. I've no idea if this would mean the glass gets too hot. Reflections are a bigger issue, so all the cinema glass is anti-reflective coated. They also have basically no colour cast and 99%+ transmission.

You can buy anti-reflective coated glass sheets, from this sort of place, https://hometheatreglass.com/ or https://www.visionteksystems.co.uk. The American place sells a 30 x 30cm 6mm thick piece for $80, and they appear to ship to the UK. I bought a much smaller piece, about 10x10cm for a uni project years ago, and it was about £30 or so, but I can't find the place I got it from.

Dirk Diggler · 5 Jul 2020 at 16:25

Just open the cabinet door when you're watching the movie.

Puzzled · 5 Jul 2020 at 23:29

Does the glass need to hold any weight? I'd be tempted to buy a cheap frame that comes with some standard 3mm glass just to test the idea.

Would probably want 6mm though if u plan to put anything on it, might get away with a bit less.

Cheaper glass will have a green tint which becomes more apparent the thicker it gets but optically clear glass isn't much more expensive but whether that will distort the image I have no idea I'm afraid.

A removable panel sounds easier as you'll need to keep the glass spotless.

NickK · 6 Jul 2020 at 08:01

tres said:
OCUK is probably the most eclectic group I know, so here's hoping someone might know about optics..

I want to enclose a laser light source (projector) in a cabinet, and would like to cover said source with a glass panel. The laser projector & cabinet sit just next to the wall it projects on to.

I've gone down a Wikipedia hole reading about different glass compositions and refractions, but need some more expert advice.

what would be an ideal glass to use for the cabinet top, whilst minimizing refractive distortion?

(Existing cabinets that incorporate a glass top cost about 10k)

Thanks!!

It's possible to put a projector in a case of glass however it gets so complicated with different bending of light for different wavelengths or the image quality suffers. You can get high grade optically less interactive glass but in the end a glass sheet is a lens by itself. You could paint the inside of the glass with a light absorptive paint except where there's the projection path, this then reduces the dispersion.

I could have asked the PHDs in the photonics lab at work but with covid they're in their own little bubble in their blackened little rooms with lasers bouncing around.