Second-order nonlinearities of molecular films studied with 20 fs pulses

The resonant and nonresonant second-order nonlinearities of molecular films with a time resolution of 15 fs are examined. The experiment used polycrystalline pentacene films of 300 nm thickness which consist of crystallites with the long axis of the pentacene molecules nearly parallel to the normal of the substrate. For second harmonic generation, a self modelocked Ti:sapphire oscillator provides 18 fs pulses which are tunable between fundamental wavelengths of 770 and 870 nm. An external prism compressor serves for minimizing the pulse duration at the location of the pentacene sample.