P.S. i always wanted to try this Pink Floyd Cover*, but if you download a trial of Thea Render
and check their sample scenes to download (Laser Lab) or look at their fantastic gallery, you
will see of course much better sample images, regarding this.
*I tried this with the free Lux Render years ago and Blender, but could not get the light beam
parallel, due to the lack of knowledge at this time.
I haven't followed this whole thread (Gaussian Mirror) but I suppose that the rainbow effect and the refraction
are "simulated" and not physically rendered with the unbiased engine of Thea.
I say this because for what I've tested so far, doing a simple 4k render of a scene like this
took almost 8 hours on my i7-7700K and unfortunately the Unbiased engine of Thea is not GPU bound (like the superfast Presto engine on my 1080 Ti).
But if you have tons of cores then it should be possible to render a "physically" calculated refraction rainbow :)
