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I'm not entirely sure if this is on-topic here, since it's about stage lighting rather than audio or video directly, but I'll give it a shot.

I've been looking at various types of laser stage lighting, and I'm trying to work out how they work internally. I figure the scanning lasers (single fast-moving beam) work by firing a single laser onto a rotating mirror, or a mirror controlled by servos for more precise movements.

However, I can't figure out how the cluster lasers work. I'd guess there's some kind of prism in there, or some trickery with a set of mirrors and lenses that somehow "split" the beam, but I can't quite figure it out. My first thought was a fixed prism, but that wouldn't explain how these devices can spread, focus and rotate the beams.

How do these laser effects usually work?

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The question as to whether lighting questions are on topic or not has been asked, though I don't think it's been settled. There are a number of questions tagged [lighting], though most of those have a production angle. You're a little bit in uncharted territory here. –  JoshP Dec 10 '12 at 23:26
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The way most stage laser effects work is by using a holographic plate or diffraction grating which splits the single beam up into multiple beams.

[image removed due to a DMCA request from copyright holder]

These then pass to further holographic elements to provide shapes and lines, and these can then be manipulated further with lenses or mirrors.

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That's pretty cool. So it works a little bit like the double-slit experiment? –  Polynomial Dec 11 '12 at 8:53
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Very much so - when I did my laser optics course we actually used double slit slides, but apparently now holographic plates are all the rage, and can produce from 2 to millions of individual beams! –  Dr Mayhem Dec 11 '12 at 8:57
    
I'll have to look into holographic plates. Might warrant a post on physics.SE, actually. –  Polynomial Dec 11 '12 at 9:12
    
Any idea what a good search term is for finding these plates? eBay produces some undesirable results if you search for "holographic plate". –  Polynomial Dec 11 '12 at 9:49
    
"holograph laser elements" seems to work okay –  Dr Mayhem Dec 11 '12 at 10:03
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