Enhancement of the optical Kerr effect by photobleaching in nanostructured indium-doped zinc oxide thin films

A modification of the nonlinear refractive index exhibited by indium-doped zinc oxide thin solid films deposited by an ultrasonic spray pyrolysis technique, after strong femtosecond laser irradiation, is presented. We used a standard time-resolved optical Kerr gate configuration with 80fs pulses at 830nm in order to study the third-order optical nonlinearities of the samples. A significant enhancement of the optical Kerr response was obtained by intense femtosecond excitation, which induced a permanent bleaching in the sample. A quasi-instantaneous pure electronic nonlinearity without the contribution of nonlinear optical absorption was observed. There is a close relationship between the change in linear absorption induced in the indium-doped zinc oxide film after high-intensity irradiation and the strong third-order nonlinearity that develops in the irradiated film.