摘要
We experimentally demonstrate third-harmonic generation(THG)in gases ionized by a femtosecond laser pulse superimposed on its second-harmonic(SH).The mechanism of THG has been investigated,and it demonstrates that a third-order nonlinear process dominates at low pump intensity.Asymmetric third-harmonic(TH)spectra are observed at different time delays in two color fields,which are attributed to the process of the four-wave mixing(FWM)of the broad spectrum of pump pulses.A joint measurement on the terahertz(THz)and the TH is performed.It reveals that the optimized phase for the THG jumps from 0 to 0.5πas the pump intensity increases,which is different from the THz being a constant,and indicates that the THG arises from the nonlinearity of the third-order bound electrons to the tunnel-ionization current.
作者
孟从森
宋盼
吕治辉
王小伟
张栋文
赵增秀
袁建民
Congsen Meng;Pan SongZhihui Lyu;Xiaowei Wang;Dongwen Zhang;Zengxiu Zhao;Jianmin Yuan(Department of Physics,National University of Defense Technology,Changsha 410073,China;Department of Physics,Graduate School of China Academy of Engineering Physics,Beijing 100193,China)
基金
supported by the National Key Research and Development Program of China(No.2019YFA0307704)
the National Natural Science Foundation of China(Nos.11974425 and 11974426)
the National Safety Academic Fund(No.U1830206)。