Diffusional enhancement of volume gratings as an optimized strategy for holographic memory in PQ-PMMA photopolymer.

The dark enhancements of diffraction efficiency in single and multiple gratings are investigated theoretically and experimentally in phenanthrenequinone doped poly-(methyl methacrylate) materials. It is demonstrated a possibility to improve holographic characteristics of the material via the enhancement. Nearly 17-fold increment of diffraction efficiency is observed after exposure. The dependences of PQ's concentration on the rate and increment of dark enhancement are achieved quantitatively. And the enhancement in multiplexing is presented as a simple and efficient method to improve response of the material and homogeneity of diffraction efficiency. PQ's diffusion and enhancement process of refractive index modulation are simulated by a diffusion model for describing enhancement dynamics qualitatively and quantitatively. This study provides a significant foundation for the application of dark enhancement in holographic storage.