Refraction without reflection

[NormanHadley]

Hi all. I'm trying to make an image that plays with prisms in a tribute to the great Pink Floyd and the equally great Dries. I'm not necessarily after realism because I want to show a beam of white light refracting through successive prisms. This is what I have so far, but the reflected beams are swamping the refractions. Is there a way to stop the reflections?

At the moment I have a gem material with

• Refractive Index=3
  Transparency=1
  Roughness=0
  Abbe=10
  Dispersion Sample=52
  Internal Culling=Unchecked

(I know these values are unnatural - just trying for a visual effect)

Any thoughts?

[NormanHadley]

Also, I don't know why the double-refracted beam is so pixelated, when the real-time window is pretty clean and I have "Use real-time settings" checked. Here's a screenshot.