Optical Nonlinearities of Composite Materials

The implementation of promising applications of nonlinear optics in the optoelectronics field depends on the availability of nonlinear materials possessing a large and fast nonlinear response. Research in this domain was for many years concentrated on homogeneous media, both inorganic and organic. Recently however, a few groups have studied the new properties originating from heterogeneous composite materials. Two processes may make them very attractive : local field correction and carrier confinement. We have, for example, investigated the nonlinear properties of metal colloïds (gold and silver) , whose linear properties had been extensively studied previously. Near the surface plasma resonance, their nonlinear response shows a dramatic enhancement. It is very fast (subpicosecond) and for volume fractions as small as a few 10−6 their Kerr susceptibility is of the same order of magnitude as that of CS2. This also allowed us to measure for the first time the Kerr susceptibility of these metals.