Second harmonic characteristics of photonic composite glass layers with ZnO nanocrystallites for ultrafast applications

ZnO nanocrystalline thin layers are of growing interest for ultrafast optical applications. Previous investigations delivered different values of second order susceptibilities. The quantitative contribution of grain structure - depending on fabrication procedure - is not well understood. For our investigations, pure and doped polycrystalline and amorphous ZnO thin filmes of 0.1 to 1.5 μm thickness have been prepared by spray pyrolysis and alternative techniques. Texture, thickness and further structural properties of the layer have been characterized by SEM, AFM, XRD, and optical spectroscopy. Using 20-fs Ti:Sa laser pulses centered at 800 nm, we measured the angular dependence of SHG intensity and determined second order susceptibilities. For a small range of crystallinity parameters, pronouced SHG efficiencies appear. From our experiments, design parameters for ZnO nanolayers can be derived which enable a tailoring of sandwich structures for advanced non-linear processing and femtosecond laser autocorrelation.