I have a question that hopefully can be resolved here. In looking over ideal GG surfaces, and materials, the most expensive and potentially most effective are micromachined acrylic surfaces.
This beattie tech doc
http://www.intenscreen.com/pdf/focusing_screens.PDF describes a holographic surface relief diffuser and a microlens array. For non-static GG purposes, I would assume you need the surface diffuser, minus the micro lens array.
So the big question is concerning the relative efficiency of these surfaces over the traditional sand blasting, grinding or sanding treatments for glass and plastic?? I would surmise that an engineered surface (with structured surface structure) might be prone to chromatic aberations/fringing if it was spinning or vibrating. Anyone?