Reversed dispersion of light - Merging colors into white ray

[Gabiru]

Hello ive been trying to recreate Pink Floyd Dark Side of the Moon album cover art, if you dont know the backside of the album has the reversed dispersion on it, merging all the colors in a single white ray, so that would create a loop with the front side.
After a few tests i could achieve the dispersion of the white ray into the colors but i cant merge them, what am i missing here? Is this possible to recreate?

[romullus]

You may want to google the topic, it looks it's not as simple as adding second reversed prism on the path of the beam.