Long-term performance studies in a photorefractive polymer composite

The temporal evolution of the steady-state holographic performance and the response time were investigated in a low glass-transition temperature photorefractive (PR) polymer composite. With a constant poling field applied and under continuos illumination during seven days, 100 writing cycles of one hour duration were performed. We found a slight increase of the steady-state performance over time, while the response time decreased by a factor of three, clearly indicating an aging process. The device did not show phase separation or optical damage after this extended measurement period, but the exact nature of the aging process remains currently unclear. This study shows that holographic long-term measurements are important for an accurate characterization of photorefractive materials which are taken into consideration for applications. Especially changes of the response time during long-term usage have to be taken into account.