We demonstrate unexpectedly strong second harmonic generation (SHG) in argon gas by use of spatio–temporally focused (SF) femtosecond laser pulses. The resulting SHG by the SF scheme at a 75 cm distance shows a significantly enhanced efficiency than that achieved with conventional focusing schemes, which offers a new promising possibility for standoff applications. Our theoretical calculations reasonably reproduce the experimental observations, which indicate that the observed SHG mainly originates from the gradient of non-uniform plasma dynamically controlled by the SF laser field.
© 2014 Optical Society of America
Original Manuscript: November 14, 2013
Revised Manuscript: December 26, 2013
Manuscript Accepted: January 9, 2014
Published: February 11, 2014
Guihua Li, Jielei Ni, Hongqiang Xie, Bin Zeng, Jinping Yao, Wei Chu, Haisu Zhang, Chenrui Jing, Fei He, Huailiang Xu, Ya Cheng, and Zhizhan Xu, "Second harmonic generation in centrosymmetric gas with spatiotemporally focused intense femtosecond laser pulses," Opt. Lett. 39, 961-964 (2014)