Optical nonlinearity in a film of water in oil microemulsion

Optical nonlinearity by an optically thin film of water in oil microemulsion (AOT/water/decane) is reported and studied by self-phase modulation. Water in oil microemulsion is a system of spherical droplets of water coated by a monolayer of surfactant molecules, immersed in oil. The AOT molecules have a bulky tail and a small head so that the coating film has a spontaneous curvature towards water. Owing to this reason, water droplets are quite stable and from 10°C to 50°C, a large one-phase region, called L2 phase, extends in the ternary phase triangle from the decane corner into the middle of the phase diagram. A percolative transition from electrically insulating status at low temperatures to an electrically conducting status at higher temperatures is found in this region. The phenomenon occurs near the percolation line and far from the one-phase two-phases boundary line. At this point, the material turbidity is very low. Optical theory is introduced for a quantitative analysis of results. From an applicative point of view, we observe that the material appears to be suitable for several nonlinear optical devices.