Evaluation of polymerization and diffusion times in holographic recording for acrylamide-based photopolymer film

摘要

In acrylamide-based photopolymer films, holographic recording processes can be characterized by "polymerization time" and "diffusion time." Our films contain acrylamide (monomer), triethanolamine (radical initiator) and methylene blue (dye sensitizer) in a polyvinyl alcohol matrix for holographic recording by a He-Ne laser at 633 nm. In this study, diffraction-efficiency growth during holographic recording and angular response of diffraction efficiency after recording were measured. There were nine holographic samples with moderate index modulation and eight samples with overmodulation. Polymerization and diffusion times were determined from the measured diffraction-efficiency growth by curve fitting based on the first-harmonic diffusion-based model. In the curve fitting, film thickness estimated from the measured angular response was used. The evaluated polymerization time ranged between 2.8 to 6.8 sec, and no difference between the two types of index modulation was observed. On the other hand, diffusion time ranged between 3.7 to 35.8 sec, and was found to be clearly dependent on the resultant index modulation of the recorded films. Moreover, both times were found to be slightly dependent on film thickness.