Characterization of photopolymerization by a holographic technique applied to a scattering hydrogel

A holographic technique, which consists of writing a phase grating onto a photopolymer layer and recording the time evolution of its diffraction efficiency, is presented for a scattering hydrogel. The influence of photopolymer thickness and writing laser intensity is investigated. Writing parameters that yield maximum diffraction efficiency are determined. A thickness greater than 1/3 of the scattering length results in the diffusion of light in the sample, leading to a decreased diffraction efficiency of the grating. This behavior can be explained by a combination of chemical diffusion and optical scattering. Finally, a calibration of diffraction efficiency with respect to a gel and sol fraction is presented.