Abstract

Filamentation of ultra-short laser pulses in gases is an emerging technique for versatile applications reaching from pulse-compression in the few-cycle regime to frequency generation into the THz regime. Moreover, radiation in the short wavelength range is generated by filaments. Especially, the third harmonic (TH) is generated within a filament usually on a cone [1,2]. In this paper, we demonstrate on-axis TH generation in a filament in air by establishing a pressure gradient. We report on an increase of the on-axis conversion efficiency by 2.5 orders of magnitude.

© 2011 Optical Society of America