Probing nonperturbative third and fifth harmonic generation on silicon without and with thermal oxide layer

We examine Si with and without additional SiO2 thin film coating as a candidate for producing powerful 3rd and 5th harmonics of Ti:sapphire laser pulses for future spectroscopic application. Polarization rotation experiments have been performed at different incident angles to determine the origin of the generated harmonics and a strong polarization-dependency of the harmonic signals was observed. A simplified tensor formalism is introduced to reproduce the measurements with high accuracy. Comparing the measurements with the Oh symmetry of the bulk crystal, the C(2v )structural symmetry for the uncoated Si sample and a C-4v symmetry for the SiO2 coated sample, we conclude that the polarization anisotropies are determined by the surface/interface symmetries.