Third Harmonic X-waves Generation by Filamentation of Infrared Femtosecond Laser Pulses in Air

Abstract

We report the first measurement of the hyperbolic featured angularly resolved spectra of the X-shaped third harmonic generated in infrared femtosecond pulses pumped filament in air. We show that at low pump intensity, phase matching between the fundamental and third harmonic waves dominates the nonlinear optical effect and induces a ring structure of the third harmonic beam; whereas at high pump intensity, the dispersion properties of air begins to affect the angular spectrum, leading to the formation of nonlinear X-wave at third harmonic.