Polarization properties of optical harmonics generated by femtosecond Cr:forsterite laser pulses in SiC nanopowder films

Polarization properties of the second and third harmonics generated by 75 fs pulses of a Cr:forsterite laser in polymer films doped with SiC nanopowders are studied. The processes of second- and third-harmonic generation in such films originate from different nonlinear sources, giving rise to harmonic signals with different polarizations. The second harmonic, produced in randomly oriented anisotropic noncentrosymmetric SiC nanocrystals, is shown to be totally depolarized. By contrast, the third harmonic, mainly generated in the isotropic polymer material, is preferentially polarized along the polarization vector of the pump field.