Fifth-order nonlinear optical response of Alq3 thin films

The fifth-order optical nonlinearity of Tris-(8-hydroxyquinoline) aluminium (Alq3) thin films deposited on quartz substrates when exposed to an intense laser excitation of mid-infrared femtosecond pulses is investigated. This property was examined by generating the fifth-harmonic frequency of the driving field whose signal strength as a function of laser intensity is well described by a power-law scaling. The perturbative nature of the underlying mechanism enabled the linking of the process directly to the fifth-order nonlinear optical susceptibility χ(5). We also utilized the open-aperture z-scan for studying the nonlinear absorption aspect of the third-order nonlinear optical properties of the sample. It was found that Alq3 thin-films inherit the same saturable absorption character reported in Alq3 solutions under continuous laser excitation in the visible range, with a comparable value of the nonlinear absorption coefficient βeff (in the order of 10−2 cm/W).