Effect of glycerol on a diacetone acrylamide-based holographic photopolymer material

The composition of the low-toxicity, environmentally compatible diacetone acrylamide (DA) photopolymer has been modified with the inclusion of different additives. The addition of glycerol to the photopolymer composition is described. Results show that the incorporation of glycerol results in a uniform maximum refractive-index modulation for recording intensities in the range of 1-20 mW/cm². This may be attributed to glycerol's nature as a plasticizer, which allows for faster diffusion of an unreacted monomer within the grating during holographic recording. An optimum recording intensity of 0.5 mW/cm² is observed for exposure energies of 20-60 mW/cm². The modified photopolymer achieves a refractive-index modulation of 2.2 × 10^-3, with diffraction efficiencies up to 90% in 100 μm layers. Glycerol has also shown to reduce the rate of photobleaching of the DA photopolymer. This is possibly due to more prevalent inhibition effects caused by increased oxygenation of the photopolymer layers. The stability of the photopolymer samples is also improved with the addition of glycerol.