Nonlocal photopolymerization effect in the formation of reflective holographic polymer-dispersed liquid crystals

The optical performance of reflective holographic polymer-dispersed liquid crystals (H-PDLCs) is investigated as a function of sample thickness and laser exposure intensity, and, the data are analyzed in terms of a nonlocal photopolymerization model. The intensity of laser exposure is proven to have a strong influence on the reflection efficiency of H-PDLCs. We have found that the experimental results cannot be completely interpreted by the previous local diffusion model. Combined with transfer matrix analysis, a modified diffusion model with a nonlocal photopolymerization term is proposed herein, which qualitatively describes our experimental observations. The experimental data demonstrates our assertion that the nonlocal effect is strongly correlated to the exposure conditions. Under the low exposure condition, the diffusion effect is screened by this nonlocal effect, and effectively a small diffusion constant is observed. Under the high exposure condition, the nonlocal effect can be suppressed and the modified diffusion model can be deduced to the original local diffusion model. Also, within the framework of this nonlocal model, overexposure can be properly explained.