Good morning (o;
Trying to do an animation where I have a rotating prism mirror where a laser light should be bounced off of it.
Basically similar as in the older laser printers where the laser beam gets reflected from a prism mirror and hits then the exposure drum.
Tried with a spotlight close to the prism with a spot size of 1° (can’t be smaller) and the prism with a simple glossy shader:
But the result isn’t as expected…
Is that doable at all in Blender with Cycles?
No, not really. Cycles will have difficulties to deal with this kind of situation.
In this type of scenes, it’s better just to ‘fake’ the whole thing…
Guess that @Secrop may be right as of using Geo Nodes for such a case.
Here’s what I’ve just found about your question:
Or just go ahead and type something like “laser burning in Blender” on YouTube.
Cheers
Cycles are not appropriate to simulate actual optical phenomena. 
Try LuxCoreRender (open source).
(I don’t know what the problem is, but I can’t access the site, so I’m attaching a link to the wiki document.)
Release BlendLuxCore v2.6 · LuxCoreRender/BlendLuxCore · GitHub
Think LuxCoreRenderer doesn’t even support Blender 3.x…
Actually I want to simulate how the light is deflected when the prism rotates…so do a fake design involves calculating the beam for every angle in the animation…so this would get rather complicated (o;
Maybe Octane can handle such things?
Sorry for being late, just discovered this.
LuxCore works with Blender 3.6, 4.0 and more.
Tried this with LuxCore 2.61 on Blender 3.1 on my MacBook M3 Pro.
As usual, CPU BiDir Engine looks great but converges slowly (256 samples, 22min):
With GPU Hybrid engine, clamping and denoising I get a clean remder in 16min,
but it looks not as good:
