Abstract
Nonlinear optical effects in a water-sodium bis-diethylsulphosuccinate-decane microemulsion near the percolation line and far from critical points are reported and experimentally studied. We use a pump-probe configuration: a probe red Gaussian beam from a He-Ne laser is focused by a converging lens. The Gaussian-shaped TEM00 mode of an Ar+ laser is focused behind a thin film of microemulsion that is located behind the focal plane of the probe. Observation of the temporal behaviour of the detected signal allows one to distinguish a fast negative nonlinear optical effect, attributed to thermal blooming by a slow positive nonlinear optical effect attributed to mass diffusion due to the Soret effect and electrostriction. Maximum nonlinearity is observed for parallel polarizations of the pump and probe beams. Turning off the pump beam, the thermal profile and consequent nonlinear effect disappear. The existence of the concentration profile and of the consequent converging lens effect is clearly detected by the probe beam as well as its slow erasure by thermal diffusion.