Carole Ecoffet

Photopolymerization Induced by Optical Field Enhancement in the Vicinity of a Conducting Tip under Laser Illumination

We introduce a method of local photopolymerization in the submicrometer scale. The source used is a metallic tip whose extremity presents a strong localized optical near-field enhancement (FE) when the tip is illuminated by a laser beam suitably polarized. The FE permits the polymerization threshold dose to be locally exceeded at the tip extremity while the threshold is not reached elsewhere. By this method the formation of micronic/nanometric polymer dots has been demonstrated. The preliminary results presented here validate experimentally the concept of the local optical source issued from a conducting tip.

Optimization of photo-induced 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 mm. 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 Youngs modulus pattern associated with each individual record and, therefore, optimizing the recording procedure.