I asked a question about laser stage lighting over at Audio Video Production, an

Question

I asked a question about laser stage lighting over at Audio Video Production, and received an excellent answer that explained that laser clusters are generated from a single beam via something called a "holographic plate".

I'd imagine they're made up of a crystal-like structure of materials with different refractive indices, but I'm not exactly sure. If that's the case, surely such tricks with refraction would cause component colours to be refracted at different angles, but this doesn't seem to be the case.

How do these really work?

Update: There seems to be some confusion. Cluster laser lighting units seem to be able to produce arbitrary numbers of output beams, and have some rudimentary control their direction, all from a single laser diode. I'm not asking about the principles of holograms, but rather about the mechanism by which a single laser beam passing through the plate results in multiple distinct beams coming out of the other side.

Explanation / Answer

Effectively, such a holographic plate is nothing more than a 2D diffraction grating. A typical diffraction pattern of such a grating is shown here.
I added a link to my answer that highlights the orthogonal superposition of two diffraction gratings as an example of a 2D grating. By the way: in the picture that you provided the grating probably is a simple 1D grating (the beam appears to splits in only one direction).

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