Two way diffusion model for the recording mechanism in a self developing dry acrylamide photopolymer

In our most recent study diffusion constants were measured in the simplified monoacrylamide version of a dry acrylamide based photopolymer holographic recording material developed in the Centre for Industrial and Engineering Optics. In this paper we report diffusion constants for the commonly used photopolymer formulation, which also contains the crosslinker bisacrylamide. A physical model for the recording mechanism is proposed which explains the two way diffusion observed in both systems, and is in agreement with much of the previously observed behaviour of the material, particularly in regard to dependence of diffraction efficiency growth on spatial frequency and persistence of holographic gratings under uniform exposure. The model is also supported by direct observation, under a surface profiler, of the boundary between an illuminated and un-illuminated area at the photopolymer surface.