Process optimization for the manufacturing of holographic elements using Darol photopolymer

Abstract

Design and manufacturing of high efficiency and reliable volume phase holographic optical elements require photosensitive materials where the performances of the device are straightforwardly related to the recording and post process parameters. In this context, Darol® photopolymers are promising materials since the modulation of the refractive index is set during the thermal process that follows the holographic exposure. In the present study, dry Darol® films are thermally processed to determine the optimized conditions to achieve a large modulation of the refractive index together with good optical properties of the hologram (i.e. transparency), flatness and homogeneity. For each condition, volume phase gratings are written and characterized in terms of diffraction efficiency. A threshold temperature of 150 °C is found, and only latent holograms are obtained at lower temperature, as confirmed by thermal characterizations. Moreover, a dependence of the refractive index modulation on the line density and laser intensity is highlighted.