Structural investigations of multiple gratings recorded in polymer-dispersed liquid crystals film by holography

Angular multiple transmission gratings were recorded simultaneously in acrylate-based polymer-dispersed liquid crystals film by holography. The micro-structure of the gratings was investigated through atomic force microscopy and scanning electron microscopy, and we found that with the exception of the holographic volume structure, each grating has a surface relief with the depth of tens of nanometres. The effects of surface relief on the optical and electrical performances of the multiple gratings were tested, and the results indicate that the diffraction efficiency of multiple gratings is mainly determined by the refractive index modulation of the volume structure; however, the diffraction energy of surface relief is less than 5% of the total. The results show no evident influence of the surface relief on Bragg angle and drive electric field. Through experimental analysis, it is also shown that volume shrinkage of about 2% for the gratings occurs after exposure. In addition, multiple images were recorded in this work, the readout and erasing performances were tested, and the transmission of the sample in visible spectrum was detected; our results indicate a prospective application for holographic polymer-dispersed liquid crystal film in displays or data storage.