Abstract

Incoherent second harmonic generation, in other terms - hyper-Rayleigh scattering (HRS), from the three-dimensional disordered array of silver nanocrystals with the typical size of 10-50 nm embedded in a dielectric matrix is studied using the output of a Q-switched Nd-YAG laser. The samples were prepared on the base of an exposed high-resolution photoemulsion. For the s-in, s-out geometry the HRS indicatrix is becomes essentially nonmonotonous with increase in the angle of incidence θ₀. At θ₀=70° it has a maximum near the direction of the normal to the surface, whereas for the p-in p-out combination the indicatrix remains monotonous in the vicinity of the normal (Fig. 1). The linear, or Rayleigh, scattering (RS) indicatrices measured for parallel in/out polarizations have sharp specular peaks that are absent for cross-polarization geometries (Fig. 2a). The intensity of these peaks is much larger than that of diffuse component, which indicates the presence of significant regular component in the linearly scattered light. On the other hand, there is no any noticeable specular peaks in corresponding HRS indicatrices (Fig. 2b). Both these facts testify that the fluctuating dipole optical nonlinearity originating from the local inversion symmetry breaking prevails over the regular quadrupole one in the system studied. The difference in the shapes of HRS and RS indicatrices apparently stems from the fact that HRS is due to fluctuations of both nonlinear susceptibility and local fields whereas RS is determined by the local-field fluctuations only. From the comparison of HRS and RS data we estimate the relative contributions to the incoherent second harmonic generation from the fluctuations of the nonlinear susceptibility and local fields.

© 1998 IEEE