Holographic storage stability in PQ-PMMA bulk photopolymer

Holographic storage stability is investigated experimentally in phenanthrenequinone (PQ) doped poly-(methyl methacrylate) (PMMA) photopolymer with high thickness and rigid polymer matrix. It is demonstrated that the stability consists of two continuous processes, dark enhancement and decay of holograms, which are corresponding to the diffusion of PQ and its photoproduct molecules, respectively. During dark enhancement the Bragg detuning of angle selectivity is observed. Therefore it is necessary to obtain steady holograms quality by adjusting the readout angle. After reaching steady state, the long-term stability of holograms is determined by the diffusion of photoproducts. Temperature is a most significant parameter for long-term stability, which can bring sufficient energy to increase the diffusion of photoproducts and reduce the stability. Finally low temperature and uniform exposure as alternative methods are proposed to optimize the storage stability after dark enhancement. Moreover the influence of humidity on the storage stability is neglectable.