Hyper-Rayleigh scattering in Gd-containing Langmuir-Blodgett superstructures

Incoherent optical second harmonic (SH) generation, or hyper-Rayleigh scatt ering (HRS), is used to study the structure and properties of Gd/C18H36O2 m ultilayer Langmuir-Blodgett (LB) films. SH reflection spectra tin combinati on with linear absorption spectral, HRS indicatrices, thickness dependence, and wave polarization diagrams are measured for s-polarized fundamental ra diation. The SH radiation is entirely diffuse but predominantly s polarized , with the maximum of the HRS indicatrix shifted by 8 degrees relative to t he specular direction, which is interpreted as being due to the contributio n of a fluctuating quadrupole to the nonlinear-optical response of the film s. The estimated correlation length of spatial fluctuations of the nonlinea r-optical polarization in the film is similar to 400 nm. These properties a re associated with an islandlike structure formed by Gd ions inside LB stru ctural units. (C) 2000 Optical Society of America [S0740-3224(99)01412-5] O CIS codes: 190.4710, 190.0190, 240.0310.