Abstract

We report on harmonic generation experiments and calculations in air to investigate the theoretical prediction of Kolesik et al. ( Opt. Lett. 35 , 2550 ( 2010 ) ) for testing the recently proposed higher-order Kerr effect model. Our observations show that although the fifth-order nonlinearity is non-negligible, the overall defocusing effect via the higher-order nonlinearities is sufficiently small that plasma formation should be a main defocusing mechanism in high power filamentation. We also explore cross-phase modulation via the optical Kerr effect, and find that the higher-order nonlinearities can significantly alter the phase matching of harmonic generation.