Frequency doubling and autocorrelation studies of 20-fs pulses using polycrystalline zinc oxide thin films

We demonstrate the potential of thin ZnO films for frequency doubling and autocorrelation measurements of ultrashort laser pulses. Using a spray pyrolysis technique, ZnO films of submicron thickness were deposited on glass substrates. Such thin films show an effective second-order nonlinearity larger than that of beta-barium borate and negligible group velocity dispersion for input wavelengths around 800 nm. Autocorrelation measurements performed with 20-fs pulses from an 88-MHz modelocked Ti:sapphire laser show a nonresonant, instantaneous nonlinear response of the material and a dynamic signal range of two orders of magnitude for average input powers down to 10 mW.