Enhancement of third harmonic generation in femtosecond laser induced filamentation – comparison of results obtained with plasma and a pair of glass plates

Abstract

We experimentally demonstrate that significant enhancement of third harmonic generation during filamentation in air can be achieved by terminating a filament with either a pair of uncoated glass plates or a thin plasma string created by a second laser pulse. By comparing the results obtained under these two conditions, it appears likely that the inserted plasma string plays a role as a phase plate, by which the phase mismatch induced by the Gouy phase can be partially corrected.

Keywords:

• filamentation
• femtosecond laser pulses
• third harmonic generation
• plasma
• Gouy phase

Acknowledgements

The work is supported by National Basic Research Program of China (Grant 2011CB808102), National Natural Science Foundation of China (Grant Nos. 10974213, 60825406, 11074098). Y. Cheng acknowledges the support of National Outstanding Youth Foundation.