Shrinkage study in photopolymerisable hybrid sol-gel through holographic patterning

Photopolymerisation-induced shrinkage of holographic materials is one of the main factors, which needs to be considered for designing holographic optical elements (HOEs) with high accuracy in light redirection with maximum efficiency. This work studies the shrinkage in photopolymerisable hybrid sol-gel (PHSG) by examining the properties of volume transmission gratings recorded in PHSG layers. It explores both the dependence of shrinkage on the holographic grating parameters (thickness, spatial frequency, slant angle) and the effect of material aging. By using the fringe-plane rotation model, shrinkage is found to have the maximum value of 1.37% at 765 lines/mm (19.36° slant angle) and 7.91% at 2025 lines/mm (16.88° slant angle) in 25 days old layers. The obtained shrinkage is in the same order of values reported for other holographic materials, which demonstrates the potential of PHSG for the development of HOE with optimum performance.