I'm basically looking for a material that can allow photons to pass through its cavities, but only those photons that travel at an angle (almost) exactly perpendicular to the materials surface. Non-perpendicular photons should be absorbed by the material upon impact as much as possible.
I can imagine perhaps a stack of graphene sheets, or a bunch of parallel carbon nanotubes? Or maybe a high precision laser drilling through ...something else? Clearly I'm no chemist or material scientist, so I'm hoping to tap into the knowledge of this community.