Approximating monomer diffusion in the Raman-Nath regime

In photopolymers knowing the rate of diffusion of the monomer is of great interest in terms of modelling the evolution of recordings and predicting material behaviour. A wide range of values have been proposed using various indirect optical measurement techniques. A method involving the recording of very large period gratings, i.e. which diffract in the Raman-Nath regime, has been proposed, the results of which have been interpreted to suggest a diffusion rate of the order of 10(-8)cm(2)/s. Using a similar acrylamide and polyvinylalcohol based material, the experiment involves monitoring the evolution of the zeroth order diffraction efficiency, the decay of which it is assumed is solely due to diffusion of the monomer. Repeating these experiments for different periods and for coverplated and uncoverplated layers, we offer a more complete analysis of the processes taking place indicating that not only is a volume holographic grating formed but also a surface relief profile. Evolution of both the holographic and the surface relief gratings will have an impact on the estimated rate of monomer diffusion. Results illustrating the variation are demonstrated and from these we show that the rate of diffusion of monomer to be closer to the order of similar to 10(-10) cm(2)/s.