Conical emission and induced frequency shift of third-harmonic generation during ultrashort laser filamentation in air

We studied the spectral and angular distribution of intense third-harmonic pulses generated in atmospheric air during the filamentation of a near infrared femtosecond laser pulse. The co-filamentation of the high intensity fundamental and third-harmonic pulses induces a spectral shift of the third-harmonic pulse as a function of the fundamental power. The third-harmonic conical emission is red-shifted while its central part blue-shifted. The experimental results are in good qualitative agreement with the results of numerical simulations.