Efficient generation of third harmonic radiation in air filaments: A revisit

In this paper we revisit the third harmonic generation from a femtosecond laser filament in air and its significant enhancement (similar to 100 times) with a intercepting pump pulse, which has been reported very recently. The enhanced third harmonic is studied as a function of the pulse polarization, time delay between the pump and signal pulses, laser pulse energy. etc. We provide an explanation for the enhancement of third harmonic based on a quenching of interference effects present near filamentation threshold. Simulations based on a two-color propagation code reproduce well the experimental observations and confirm our interpretation. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.