Scanning electron micrographs of volume phase, reflection holograms recorded in DMP-128 reveal microstructure that is responsible for holographic efficiency. Solid and porous payers alternate with a spacing commensurate with the recorded fringe pattern. The difference in material density between the solid and porous regions accounts for the refractive index modulation and therefore the holographic activity of DMP-128 holograms. The pores of the hologram are interconnected and are filled with many low and moderate viscosity liquids upon immersion. Important optical properties of the holograms are profoundly and predictably affected by filling of the hologram pores.
R. T. Ingwall,
"The Mechanism Of Hologram Formation In DMP-128 Photopolymer", Proc. SPIE 0883, Holographic Optics: Design and Applications, (12 April 1988); doi: 10.1117/12.944129; https://doi.org/10.1117/12.944129