Diffuse optical harmonic generation in SiC nanopowder films: hunting scattered photons

Second- and third-harmonic generation in polymer films doped with silicon carbide nanopowders is experimentally studied in the regime of weak scattering, with the size of nanoparticles a, the elastic scattering length l, the radiation wavelength lambda, and the film thickness L meeting the relations a<lambda<lsimilar toL. The strong wavelength dependence of diffuse second- and third-harmonic generation observed under these conditions indicates a significant role of scattering effects in nonlinear optical interactions in nanopowder materials, which allows diffuse harmonic generation to be controlled by varying the ratio of the characteristic size of the nanoparticles to the wavelength of the pump radiation. The contribution of scattering-delayed pump photons to diffuse third-harmonic generation in a SiC nanopowder film is visualized by measuring the third-harmonic intensity as a function of the delay time between two pump pulses.