Optimization of photoinduced polymer microstructuration using atomic force microscopy

Photopolymerizable materials are capable of recording high-efficiency volume holograms by changing the refractivity of the layer, for fringe spacing between 0.2 and 10 mum. As the photosensitive emulsion is embedded between two glass plates, it is possible to open the sandwich after the recording and to analyze the free polymer surface using pulsed force mode of an atomic force microscope. The modulation of properties between the bright and dark fringes, photoinduced by an interference pattern are analyzed in terms of : - relief amplitude (the surface corrugation appearing after opening is due to the relaxation in surface of the constraints stored during the grating formation); - local variations of the mechanical polymer properties (they are related to the coupling of the spatially controlled photopolymerization with mass diffusion processes, giving rise to the microstructuration, e.g. regions with various segment densities). Taking into account all these data, improvement of the material is possible in view of applications in data storage or creation of optical diffractive elements. In particular, in the case of multiplexed gratings, it provides a means for visualizing the Young's modulus pattern associated with each individual record and, therefore, optimizing the recording procedure.