^ there are some different ways for do that, the 2 more easy ones that came in mind are these ones:
different "fans" in this way:
but this can cause some problems, cause for the different inclinations, you have to displace your hands more, passing a semitone, and can "hit" involuntarily a beam different than the one you want.
Or, as alternative, combining the beams with a dichro, that gives you more different possibilities:
Green and yellow, red and green, or red and yellow beams, depending how you decide to drive the beams for the 2 combinations tones/semitones ..... other than this, all the beams remain on the same plane.
There is also a possible "cheap" way for change volume (or intensity, or flanging, or modulation, or whatever function you want to give it), using 2 or 3 light sensors with a linear diaphragm for have an indication (not precise, but still enough) of the distance of the hand, using this distance as supplementar control parameter, if you want to be a "bad boy" (no offenses, just a common word joke here
)
It's all matter of how much work and programming you want to put in it ..... but, for sure, you can end with a machine that none of the commercial builders sells, actually :beer: