No abstract

Third-order nonlinear optical properties of Au:SiO2 thin films were studied at the surface plasmon resonance wavelength by the z-scan technique using a nanosecond laser. Films were prepared by a multilayer deposition sputtering technique. They were composed of 2 nm mean diam gold particles, with a metal volume fraction of 20%. Z-scan measurements performed both with and without aperture showed a very large nonlinear absorption masking the nonlinear refraction. The nonlinear absorption coefficient β was found to be negative and equal to −1.1×10−2 cm/W. The different mechanisms contributing to this absorption are discussed and the large value of β is correlated to the duration of the laser pulses. Moreover, it is shown that a mean field theory is not appropriate to evaluate the effective susceptibility at high metal concentrations.

No abstract

A rigorous connection is established between the local porosity entropy introduced by Boger et al. (Physica A 187, 55 (1992)) and the configurational entropy of Andraud et al. (Physica A 207, 208 (1994)). These entropies were introduced as morphological descriptors derived from local volume fluctuations in arbitrary correlated microstructures occuring in porous media, composites or other heterogeneous systems. It is found that the entropy lengths at which the entropies assume an extremum become identical for high enough resolution of the underlying configurations. Several examples of porous and heterogeneous media are given which demonstrate the usefulness and importance of this morphological local entropy concept.