Investigation of the UV-resistance of photopolymerisable glass for space applications

Abstract

The progress of space based scientific research leads to an increasing demand for more efficient and less bulky instruments. Conventional refractive elements make up a critical part of many optical instruments launched into space; however, they can be bulky and heavy. Holographic optical elements are an efficient alternative to replace the conventional optical elements as they are lightweight and can be miniaturized. Current materials typically used for volume holographic optical elements are not robust enough for use in space environment. Recently a promising photopolymerisable glass has been developed using a sol-gel technique, which can provide dry layers suitable for holographic recording with a significantly lower curing time. In addition, the material has shown stability after exposure to high humidity and temperatures up to 130°C. However, its UV resistance needs to be improved in order to satisfy the requirements for application in space. The main goal of this work is to study and improve the UV resistance of the photopolymerisable glass. The following approaches have been used: 1) postrecording exposure to uniform laser beam and 2) modification of the material composition. It was found that exposing the material to a uniform beam immediately after the recording improves UV resistance and provides stability of the layer. The effect of the chemical composition of the material on its UV resistance was also studied by varying the concentration of the dye and adding Polyurethane Diol to improve its elastic properties. The performance of the material was tested by studying the optical properties of transmission gratings recorded in the layers, such as diffraction efficiency and refractive index modulation, before and after UV exposure. The first experimental results for both approaches have shown promising results and the potential routes for further developments have been identified.